VTMC 236 Epidemiology Final
Terms
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DIAGNOSTIC TESTS
GOAL
A COUPLE OF BASICS DEFINITIONS -
Distinguish between infected/diseased and noninfected/diseased individuals
Any device or process designed to detect a sign, substance, tissue change or response -
DIAGNOSTIC TESTS
TWO TYPES
AND EXAMPLES -
Pathagnomonic Tests
- Absolute Predictor
- No false positives
- False negatives possible
~~ ie dont find marker
- Culture
- Parasite Detection
- PCR
Surrogate Tests
- detection of secondary changes
- false positives
- false negatives
- Serology
- Allergy Test
~~ immunosuppresion may produce false negative -
SEROLOGICAL TESTS
4 POSITIVE INTERPRETATIONS -
Animal previously exposed to the infectious agent
Prior vaccination or passive antibody transfer
~~ colostrum
Cross Reactions
Lab Errors
- lack of standard processes -
SEROLOGICAL TESTS
4 NEGATIVE INTERPRETATIONS -
Animal non-infected or exposed
Animal recently infected/exposed
Immunologically tolerant animals
~~ PI BVD animals our favorites
Lab Errors
- lack of standard processes -
DIAGNOSTIC TESTS
3 SCALES -
Dichotomous Scale (yes or no)
- pregnancy
- virus isolation
- serologically positive
Ordinal Scale
- titer
- body condition score
Continuous Scale
- blood parameters
~~ RBC, WBC etc
- ELISA values
- somatic cell counts -
A PERFECT TEST
3 CHARACTERISTICS -
Only Exists for a Perfect Disease
If
- a certain charactersistic is ALWAYS present in patients with the disease
- that characteristic is NEVER present in patients who do not have the diseasse
- the test is able to dect that characteristic when it is present
The test is perfect and no further CLINICAL JUDGEMENT is required -
A PERFECT TEST
3 RESULTS -
All individuals without the disease of interest would have one uniform value for the test
All indivuuals with the diesase would have a different but uniform value for the test
All test results would be consisten with the results of the diseased or those on the non-diseased - REAL TEST
- Positive and Negative results produce two Normal Curves with an area of overlap
-
TEST PERFORMANCE
TWO KEY FACTORS -
Precision
- ability to producec consistent results wen repeated under the same conditions
- animal and laboratory conditions
- inerobserver variability
~~ ie agglutination interpretation requires experience
- intraobserver variablility
~~ ie how much sleep did you get
Accuracy aka Validity
- ability to produce correct results -
TEST PRECISION
THREE FACTORS -
- animal and laboratory conditions
- inerobserver variability
~~ ie agglutination interpretation requires experience
- intraobserver variablility
~~ ie how much sleep did you get -
TEST ACCURACY
THREE RESULTS -
Perfect Diagnostic Discrimination
- normal curve results do not overlap
Partial Diagnostic Discrimination
- normal curve results have partial overlap
No Diagnostic Discrimination
- complete overlap of normal curve results -
TEST ACCURACY
HOW TO GET IT -
Gold Standard
- a diagnostic method or combination of methods which determines absolutely and without error whether a disease/infection is present in an animal
OK How to REALLY get it
- 2X2 Table
~~ True Positive
~~ False Positive
~~ True Negative
~~ False Negative
- The go to town with statistical techniques -
ACCURACY
WHAT COMPRISES IT -
Sensitivity (Se)
- the probability that a test will correctly indentify infected animals
- TRUE POSITIVES
Specificity (Sp)
- the probability that a test will correctly identify non-infected animals
- TRUE NEGATIVES
Note
- Se and Sp DO NOT change with prevalence -
SENSITIVITY
MATH DESCRIPTION -
Divide True Positives by Total Diseased
Note
- total diseased = sum of True Positives and False Negatives -
SPECIFICITY
MATH DESCRIPTION -
Divide True Negatives by Total Non-Diseased
Note
- total Non-Diseased = sum of False Positives and True Negatives - INCREASE SENSITIVITY
-
Decreases number of False Negatives
Increases number of False Positives
Increase sensitivity when disease is highly contaguous or pathogenic - INCREASE SPECIFICITY
-
Decreases number of False Positives
Increases number of False Negatives -
SELECTING A CUTOFF VALUE
BUYING AND SELLING -
Purpose of test
Relative cost of false positives vs false negatives
Availability of definitive tests of High Specificity
Buying
- want high Sensitivity
~~ avoid diseased animals
Selling
- high specificity
~~ ensure sale of healthy animals -
PREDICTIVE VALUES
WHAT DO THEY DEPEND ON
NAME AND DEFINE THEM -
Depend on
- Sensitivity
- Specificity
- PREVALENCE
Positive Predictive Value (PPV)
- proportion of True Positives amoung the TOTAL number of positive results
Negative Predictive Value (NPV)
- proportion of True Negatives amoung the TOTAL number of negative results -
PREDICTIVE VALUES
FIVE TRUTHS -
Are PREVALENCE DEPENDENT measures that Characterize a Test Result
Indicate the LIKELIHOOD OF DISEASE of an INDIVIDUAL with a Given Test Result
Can be used to ESTIMATE the proportion of False Positive and False Negative Results
Are important for the understanding that TEST RESULTS MAY HAVE DIFFERENT MEANINGS FOR DIFFERENT SUBGROUPS OF A POPULATION
CANNOT be obtained by the standard 2X2 table when the Prevalence in the Table IS NOT IN AGREEMENT with the Actual prevalence in the target population - APPARENT PREVALENCE
- Number of Positive Test Results
- TRUE PREVALENCE
- Number of Diseased Animals
-
PREDICITIVE VALUE RELATIONSHIPS
TO
TRUE PREVALENCE -
Apparent Prevalence
- increases linearly with True Prevalence
Positive Predictive Value
- exponentially increases with True Prevalence
~~ tf if prevalence is low need to use a test with High Specificity
Negative Predictive Value
- exponentially decreases with True Prevalence - SERIAL TESTING
-
Animal must be positive on 1st AND 2nd test
Increases Specificity
1st Test
- Highly Sensitive
- inexpensive
2nd Test
- Highly Specific
- cost less important because testing smaller numbers - PARALLEL TESTING
-
Animal can be positive on 1st OR 2nd test
Increases Sensitivity
Works when
- neither test has high Sensitivity
- each test detects a DIFFERENT characteristic of disease -
TEST STRATEGY
SERIAL
FIVE -
Increase Specificity
Positive test result is greatest predicitive value
Rule in a disease clinically
Clinical Purpose
- use when time not crucial
- avoid excessive testing
- test and removal programs
Useful when there is an important penalty for False Positve results -
TEST STRATEGY
PARALLEL
FIVE -
Increase Sensitivity
Negative test result is greatest predictive value
Rule Out a disease clinically
Clinical Purpose
- Rapied assesssment of individual paitients
~~ vaccination clinics
~~ emergencies
Useful when there is an important penalty for false negative results
- ie missing a disease -
DIAGNOSTIC TESTING
WHEN TO USE -
Used on individuals who have a specific indication of possible illenss
Individual based
Important
- diagnostic precision and accuracy
Less Important
- acceptability of test
~~ invasivenes
~~ cost -
DIAGNOSIS
5 STEPS -
Establishement of Diagnostic Hypothesis
Highly Sensitve tests to rule out Specific diseases
Strong Clinical Suspicion
Highly Specific test to Rule In
Confirm or Reject the clinical suspicion -
SCREENING TESTS
WHEN TO USE -
Used on individuals who are Asymptomatic
Early detection of disease
- case finding
Determine status of a population
- ie infected or not
Estimate
- subclinical disease
- infection prevalence
Eradicate Diseases -
SCREENING TESTS
6 EXAM HANDY THOUGHTS -
Population Based
If proportion of affected individuals is likely to be small
- ie early detection of disease
- risk of high number of false positives
~~ tf increase specificity
~~ tf further study of positive individuals
Evaluation should focus on the whole process
Administration
- inexpensive
- low risk
- minimal discomfort -
PURPOSE OF TESTING
SEXY SIX -
Diagnosis
Screening
Monitor Vaccination Programs or Procedures
Judge Severity of Disease
- quantitiative tests
Predict Subsequent Clinical Course and Prognosis
Estimate Responsiveness to Therapy -
WHY MEASURE DISEASE
THREE AMIGOS -
Determine mechanism of transmission via Distrubution and trend of disease
- temporal
- spatial
- feeding
- husbandry
Assess the impact of disease on study population
- what is the risk of a given animal in the population having disease
Assess the effect of control progams to prevent or eradicate disease from the population -
WHAT TO MEASURE
SEVEN -
CASES
- clincal cases
- subclinical cases
- production parameters
- combinations of above
NON CASES
- may be cases in the future
- recovered cases
~~ ie immune
- required for comparison purposes - COUNTS
-
Static Measure
Simple enumeration of cases
Very LIMITED use in epidemiology
- requires Population at Risk - PROPORTION
-
Static Measure
A fraction in which the numerator is included in the denominator
Dimensionless
Range
- from 0 to 1
- % -
PREVALENCE
TWO TYPES -
A Static Measure
Always a PROPORTION
Point Prevalence aka Prevalence
- proportion of a population affected by a disease at a given point in time
- based on EXISTING cases
- P = (# individuals having a disease at a particular point in time)/(# individulas in the population AT RISK at that point in time)
Period Prevalence
- number of cases that are KNOWN to have occurred during a SPECIFIED PERIOD of time
- sum of
~~Point Prevalence at the beginning of the period
~~ # of NEW CASES that occur during the period
~~ ie incidence - RATIO
-
A Static Measure
A fraction in which the numerator IS NOT included in the denominator
With or Without Dimension
Range
- 0 to infinity
ie Odds Ratio
- ratio of
~~ probalility of occurence
~~ propablility of non occurence
Note
- CANNOT convert between prevalence and odds - RELATIONSHIP BETWEEN PROPORTION AND ODDS
-
Proportion
- = odds/(odds + 1)
Ratio aka Odds
- = proportion/(1 - proportion) - RATE
-
A Dynamic Measure
The instantaneous change in disease per unit change in time
Has Dimension
Range
- 0 to infinity - CUMMULATIVE INCIDENCE
-
CI aka Incidence Risk
PROPORTION of disease free individuals developing a given disease of a SPECIFIED TIME
Based on NEW cases
CI =
~~ # of individuals that BECOME diseased during a particular period
~~--~~ divided by
~~ # of healthy individuals in the population at the beginning of the study
Only for the FIRST occurance of disease
For Static Populations
- all animals enter study at the same time
- remain for period of study
- only "leave" study when develop disease
Can be estimated from Incidence Density
- more accurate when Incindence Density is low
- allways underestimates CI
~~ assumes all individuals are at risk for entire period - INCIDENCE DENSITY
-
I aka True Incidence aka Hazard Rate
Measures the RAPITIDY with which new cases of disease develop over time
I =
~~ # of NEW cases of disease that ocuuri in a population during a paricular period of time
~~--~~ divided by
~~ sum, over all individuals, of the length of TIME AT RISK of developing disease
Demominator accounts for different time at risk for different individuals
- ie time at risk stops once animal has disease
Expressed as an ANIMAL TIME UNIT
- can exceed 1
Can be estimated (used) when animals get disease MORE THAN ONCE
- ie mastitis
Useful for DYNAMIC POPULATIONS
Does NOT have an interpretation at the Individual level -
CUMULATIVE INCIDENCE
NUMERATOR
DENOMINATOR
TIME
UNIT
TYPE -
NUMERATOR
- New Cases
DENOMINATOR
- Initial Population
TIME
- Duration of Period
UNIT
- None
TYPE
- Proprotion
~~ involves time -
INCIDENCE DENSITY
NUMERATOR
DENOMINATOR
TIME
UNIT
TYPE -
NUMERATOR
- New Cases
DENOMINATOR
- Animal Time
TIME
- Start of study until development of disease
UNIT
- Cases per animal time
TYPE
- Rate -
POINT PREVALENCE
NUMERATOR
DENOMINATOR
TIME
UNIT
TYPE -
NUMERATOR
- Existing cases
DENOMINATOR
- Initial Population
TIME
- Single Point
UNIT
- None
TYPE
- Proportion -
PERIOD PREVALENCE
NUMERATOR
DENOMINATOR
TIME
UNIT
TYPE -
NUMERATOR
- Existing/new cases
DENOMINATOR
- Midpoint
TIME
- Period
UNIT
- None
TYPE
- Proportion - CRUDE MEASURES
-
Ingnore structure of population
- gender
- age
- breed
Comparison of crude rates misleading if population structures differ - SPECIFIC MEASURES
-
Proportion or Rates in specific population subgroups
- age
- gender
- breed
Detect and explain differences in risk of disease
- proportion
- rates
Stratification
Calsculated like crude measures but limited to specific sub groups - ATTACK RATE
-
AR
Measure of Incidence
Period of Risk is Limited
Outbreadks of Food Borne Diseases
- limited exposure period
- specific exposure agents
ArR =
~~ # animals tath develop diseas during a specified time period following exposure
~~--~~ divided by
~~ total # of animals exposed - SURVIVAL
-
S
Probability of an individual with a specific disease remaining alive for a specified length of time
S = (N-D)/N
N
- # number of newly diagnosed cases under observation during the specified period of time
D - # of deaths observed in a specified period of time -
MORTALITY RATES
5 -
Crude Death Rate =
~~ # of deaths in a given time
~~--~~ divided by
~~ Total population at risk
Cause Specific Mortality Rate =
~~ # of deaths attributable to a cause
~~--~~ divided by
~~ total # of animals
Case Fatality Rate =
~~ # of deaths attributable to a disease
~~--~~ divided by
~~ total # of animals having the disease
Age-Specific Death Rate =
# of deaths within a certain age group
~~--~~ divided by
~~ total # of animals in the age group
Proportions Mortality Rate =
~~ # deaths due to specific cause of interest
~~--~~ divided by
~~ total deaths in population - General Fertility Rate
- # of live births out of the average number of females of reproductive age
-
DISEASE PATTERNS
NAME 3 -
Temporal
Spatial
Individual -
EPIDEMIC CURVES
DEFINITION
4 TYPES -
Temporal Pattern
Describe disease occurrence over time
- ploted as frequency histogram
Endemic
- disease occurs at expected frequency
Epidemic
- disease occurs at greater than expected frequency
Sproadic
- single case
- cluter of cases
Pandemic
- humungous epidemic
- international -
ENDIMIC DISEASE
4 CRITERIA -
Disease present in population of region at all times
Usually low and predictable level
Tend to have only nimor fluctuations in frequency pattern over time
A isease may be endemic at ANY level of occurence -
ENDEMIC DISEASE
4 TYPES -
Holoednemic
- most/all animals are affected
Hyperendemic
- high proportion of animals are affected
Mesoendemic
- moderate proportion are affected
Hypoendemic
- relatively small proportion are affected - CHANGES IN ENDEMIC DISEASES
-
Objective
- identify periods of high of low risk to determine possible causal factors of disease
Determination of 3 Fuerther Temporal Trends
- cyclic variation
~~ ie flu balance of new strans and immunity
- seasonal fluctuations
~~ vector borne summer fall
~~ food poisoning summer
- secular(long term) trends
~~ wont be seen without analysis
Analyses
- data plots
- time series analysis
- regression analysis
- try to determine causes of time of flucuation
~~ prediction
~~ prevention -
EPIDEMIC DISEASE
4 CRITERIA -
Incidence exceeds expected
Usually infectious diseases or poisoning
Point source or propagated
Outbreak
- localized epidemic
~~ area
~~ population -
POINT EPIDEMIC
4 FACTORS -
Single common exposure
Does not spread
Steep Curves
Often foodborne disease outbreaks -
PROPAGATED EPIDEMIC
7 FACTORS -
More gradual curve
Often involves vectors or carriers
Diseases with longer incubation periods
- Primary then Secondary case clusters
Cases may occur ove prolonged period of time
Ascending Curve Slope
- incubation period
- characteristics of agent
~~ ie infectivity
- characteristics of host
~~ ie susceptability
- population density
~~ ie contact rate
Plateau Duration
- availability of susceptible individuals
Decending Curve Slope
- immunity
- recovery -
SPORADIC DISEASE
5 FACTORS -
Infrequent diseas occurence
Irregular and unpredictable
Environmental Changes
Relaxation of control measures
Vaccination Failures -
EPIDEMICS HAPPEN
WHY
3 WAYS -
Introduction of an agent into a setting where it has not been previously
- ie WNV, SARS
- THE DREAD GAMBIAN RATS
- no immunity
A Recent increase in the amount or virulence of the agent
- antibiotic resistence
- AI our favorite
An enhanced mode of transmission
- more animals exposed
~~ SARS
~~ foodbourne diseases -
EPIDEMIC INVESTIGATIONS
7 OBJECTIVES -
Indentification of the infectious agent
Establishment of the infection source
- THAT WOULD BE STU
Establishement of the main infection transmission route and vector
Control and prevention of additional cases
Evaluate existing prevention statigies
Gain knowledge
- research
Training -
EPIDEMIC INVESTIGATIONS
THE QUESTION - Are the cases in excess of the expected baseline rate for disease and setting
-
ESTIMATION OF THE INCUBATION PERIOD
4 NEED TO KNOWS -
Index Case
- THAT WOULD BE STU
Peak
Cause
Time of exposure
- knowledge about common exposures helpful -
ESTIMATION OF THE INCUBATION PERIOD
2 ASSUMPTIONS -
Presence of clinical signs indicates disease
Health before onset of illness -
ESTIMATION OF THE INCUBATION PERIOD
FOR PROPOGATED EPIDEMICS - Difficult
-
SPATIAL PATTERNS
WHAT ARE THEY FOR TWO -
Variation between regions and countries
- important determinants of disease distribution
- environmental factors vary among locations
Local Patterns
- pen
- litter
- herd
- animals and managment can vary within farm -
SPATIAL PATTERNS
WHAT DO THEY DO 3 -
Answer the where question
Indentify occurrences of events that happen close together in space
Generate research hypotheses -
SPATIAL PATTERNS
3 VARIETIES -
Random
Regular
- usually poisonings
~~ ie contaminated water
Contagious
- little clusters -
INDIVIDUAL PATTERNS
7 SLICED 2 WAYS -
Within Population at Risk
Individual Characteristics which affect susceptability to disease
- Age
~~ tell me about it
- Gender
- Breed
- Immune Status
Opportunities for Exposure
- Type of production
~~ ie dairy vs beef
- Management
- Feeding Practices - DESCRIPTION OF DISEASE
-
Simple description of disease is FIRST STEP in epidemiological investigations
Temporal Patterns
- shape of curve
- duration
Spatial Patterns
- from specific housing to the globe
Host Characteristics
- age
- sex
- breed - DESCRIPTIVE EPIDEMIOLOGY
- Surveys
-
ANALYTICAL EPIDEMIOLOGY
3 BIGGIES -
Epidemiological Associations
- statistical significance
- strength
- importance -
EPIDEMIOLOGICAL STUDIES
TWO MAJOR TYPES -
Observational Field Studies
- researcher has NO CONTROL
- cohort studies
- case-control studies
- cross-sectional studies
- most common
Experimental Studies aka non-observational
- experiments
- controlled
~~ clinical trials
~~ field trials
- intervention studies
- manipulation of parameters
- apply treatments to populations -
CROSS SECTIONAL STUDIES
CHARACTERISTIC
OBJECTIVE -
animals are randomly sample at one point in time
- WITHOUT CONSIDERING HEALTH AND EXPOSURE BEFOREHAND
Objective
- estimation of disease prevalence
- to have a snapshot of the situation at a specific moment
~~ at the same time examine for
~~-- presence of disease
~~-- exposure status -
CROSS SECTIONAL STUDIES
OUTCOMES -
With Disease and Exposed
With Disease and Unexposed
Without Disease and Exposed
Without Disease and Unexposed -
CROSS SECTIONAL STUDIES
ADVANTAGES SEVEN -
Straighforward
Allows for the study of several diseases at the same time
Data based on Representative samples
- tf can generalize
Quick
Moderate Cost
Measuring Prevalence
- tf focus for further studies
First Step for prospective studies -
CROSS SECTIONAL STUDIES
DISADVANTAGES FOUR -
DO NOT measure temperal sequence
Not useful for disease with LOW Frequency
Low response rates (sample size) compromise representativeness
Potential for confounding releationships between risk factors
- ie BVD and Neosporia both cause abortions -
CASE CONTROL STUDIES
CHARACTERISTIC
OBJECTIVE -
Animals are INTENTIONALLY CHOSEN for health status
- ie NOT randomly selected
- tf cannot show prevalence
Objective
- determine the animal health status with regard to Potential Risk Factors
- preliminary causal hypothesis -
CASE CONTROL STUDIES
OUTCOMES -
RETROSPECTIVE VIEW
Cases
- which were exposed
- which were unexposed
Controls aka Non-Cases
- which were exposed
- which were unexposed
Note
- effective control goups are difficult to set
- must have same exposure as cases
- ideally animals within herd -
CASE CONTROL STUDIES
ADVANTAGES FIVE -
Disease with low incidence or conditions developing over a long time
Evaluation of multiple risk factors for one disease
Quick
Low Cost
Indirect measurement of risk with regard to exposures -
CASE CONTROL STUDIES
DISADVANTAGES FIVE -
Do not provide information on the disease frequency
Not suitable for the study of rare exposures
Data collection relient on quality of past records
Selection of an unbiased control group difficuls
Only valid for ONE DISEASE -
COHORT STUDIES
CHARACTERISTIC
OBJECTIVES -
Units (animals or herds) are INTENTIONALY CHOSEN for their exposure status
- ie Animals are initially healthy
Objectives
- Estimation of Incidence
- Estimation of Relative Risk
- Dose-Response Relationships
~~ possible because all animals healthy at start
~~ ie vaccine efficacy
- Estimation of the Attributable Fraction -
COHORT STUDIES
OUTCOMES -
From a heathy Cohort monitor over time or Look retrospectively from groups
Exposed Group
- with disease
- without disease
Unexposed Group
- with disease
- without disease
Compare incidences between two groups -
COHORT STUDIES
ADVANTAGES FIVE -
Measures the TEMPORAL sequence of events
Several effects/diseases in one study
DIRECT disease Incidence estimates
Prospective or Retrospective
Rare Exposures
- can identify because defining groups based on exposure -
COHORT STUDIES
DISADVANTAGES FIVE -
Long duration if prospective
- ie have to follow course of disease
Low Frequency Diseases
- eg BSE would have feed a lot of animals to see disease
Cost
Losses during follow-up -
CROSS-SECTIONAL STUDY
SAMPLING
TIME
CAUSALITY
RISK
COMPARISON OF RISKS -
SAMPLING
- Random Sample
TIME
- One Point
CAUSALITY
- Association between disease and risk factors
RISK
- Prevalence
COMPARISON OF RISKS
- Prevalence Ratio
- Odds Ratio -
CASE CONTROL STUDY
SAMPLING
TIME
CAUSALITY
RISK
COMPARISON OF RISKS -
SAMPLING
- Diseased
- Non-Diseased
TIME
- Usually Retrospective
CAUSALITY
- Preliminary Causal Hypothesis
RISK
- None
COMPARISON OF RISKS
- Odds Ratio -
COHORT STUDY
SAMPLING
TIME
CAUSALITY
RISK
COMPARISON OF RISKS -
SAMPLING
- Exposed
- Non-Exposed
TIME
- Prospective
- Retrospective
CAUSALITY
- through evidence of TEMPORALITY
RISK
- Incidence Density
- Cumulative Incidence
COMPARISON OF RISKS
- Relative Risk
- Odds Ratio -
CLINICAL/FIELD TRIALS
CHARACTERISTIC
OBJECTIVE -
Researcher has EFFECTIVE CONTROL of study situation
- Random allocation of animals
Objectives
- Effectiveness of any type of intervention
~~ preventative etc
- Evaluation of phrmocological products
- Test a specific ie causal hypothesis
- Validate findings from observational studies -
CLINICAL/FIELD TRIALS
OUTCOMES -
Groups Randomized from Sample
- look forward after intervention
Treatements
- with disease
- without disease
Controls
- with disease
- without disease -
CLINICAL/FIELD TRIALS
ADVANTAGES THREE -
High control on study factors
- varying degrees of control
Randomization avoids systematic errors
Strongest evidenc about causal relationships -
CLINICAL/FIELD TRIALS
DISADVANTAGES SIX -
Large Groups
Generalization of results may be difficult
- may not apply in other managemnet situations
One effect per experiment
Duration
Cost
Ethics
- justify use or treatment of animals
- but hey there are allways lots of cats -
MEASURING ASSOCIATION
THE EXAM QUESTION IS TALKING ABOUT THIS
YOU ARE THINKING ABOUT SIX THINGS -
Statistical Significance
Epidemiologic meassures of Association
- relative risk
- odds ratio
- prevalence ratio
- attributable fraction -
STATISITICAL SIGNIFICANCE
WHY -
You need to know whether the DIFFERENCES are due to
- causes you are interesed in
- natural variation
~~ ie chance the good 'ol normal curve - HYPOTHOSES TESTING
-
Ho vs Ha
Ho Null Hypothesis
- Hypothesis of NO DIFFERENCE
Ha
- Hypothesis of DIFFERENCE
By means of a statistical test you can check if Ho is true
- compare observed vs expected distribution for which Ho is true -
ERRORS
TWO TYPES -
Type I Error
- rejection of a true Ho
- error of concluding there is a difference when there is not
- alpha is the probalbility of making a Type I error
~~ tf alpha is the LEVEL OF SIGNIFICANCE
~~ 1-alpha = CONFIDENCE
~~ P values need to be less than alpha for significance
~~ alpha typically set at 0.05
Type II Error
- failure to reject Ho when it is untrue
- error of concluding that no difference existed when in fact it did
- beta is the probability of making a Type II error
- 1-beta = probability of rejecting Ho when it is false
~~ ie the POWER OF A TEST -
ERROR
POWER
CONFIDNECE -
When Truth is there is a Difference
Rejecting Ho
- is Power (1-beta)
Accepting Ho
- Type II Error
- False Negative
When Truth is there is NOT a Difference
Rejecting Ho
- is Type I Error (alpha)
- False Posative
Accepting Ho
- is Confidence (1-alpha) - P VALUE
-
PROBABILITY that the difference OBSERVED between groups is caused by CHANCE
Provides probability of whether distribution of observations is random or not
- does not provide information about association
P value for this course
- if P <= 0.05 reject Ho -
STATISTICAL SIGNIFICANCE
COMES DOWN TO TWO PARAMETERS -
Sample Size
- easier to show significance if larger
- blame inconclusive results on small sample size
~~ and apply for a bigger grant
Strength of association
- ie the REAL difference between the groups -
CHOOSING THE APPROPRIATE
STATISTICAL TEST
5 FACTORS -
Scale of Measurement of the evaluation criterion
- quantitative data
- qualitative data
Scale of measurement of the study factors
- quantitative data
- qualitative data
Existence of repeated measures
- independent samples
- related samples
Number of observations
Specific assumptions for each statistical test
- parametric techniques
~~ use if data folows normal distribution
~~ large N ie >30
~~ quantitative data
~~ lower then lower the power of test
- non-parametric techniques
~~ use when cant meet requirement for parameteric
~~ small N ie < 15
~~ qualitatiive or quantitative data
~~ has higher power than parametric when N is small -
STRENGTH OF ASSOCIATION
WHEN
WHAT
3 HOWS -
Check once Significance has been shown
Compare Occurances Between Groups
Relative Risk
- incidence
- Cohort Studies
Odds Ratio
- proportions
- prevalence
- incidence
- Case Control Studies
- Cohort Studies
- Cross Sectional Studies
Prevalence Ratio
- prevalence
- Cross Sectional Studies - REATIVE RISK
-
RR
- the relative risk of BECOMING diseased
- ie the disease is RR time more likely to occur amoung those exposed to the suspected rik factor than among those with no such exposure
The ratio of
- incidence of disease in exposed animals
~~--~~ to
- incidence of disease in unexposed animals
Range
- 0 to infinity
RR = 1
- there is not an association
RR > 1
- there is a risk factor
RR < 1
- there is a protective factor
Note
- 1 MUST BE EXCLUDED from the 95% Confidence Interval for there to be a Significant risk or protective factor - ODDS RATIO
-
OR
- The relative risk of BEING diseased
- DO NOT know if animals already diseased
- to measure whether of not exposure is more common in the diseased group than in the healthy group
- the odds of having the disease among those exposed to the suspected risk facor is OR times the odds of disease anoung those with no such exposure
The ratio between
- odds of disease in exposed animals
~~--~~ to
- odds of disease in unexposed animals
Range
- 0 to infinity
OR = 1
- there is not an association
OR > 1
- there is a risk factor
OR < 1
- there is a protective factor
Calculate from CROSS PRODUCT of 2X2 table
When disease is <10%
- OR ~= RR
Note
- 1 MUST BE EXCLUDED from the 95% Confidence Interval for there to be a Significant risk or protective factor - PREVALENCE RATIO
-
PR
- the relative risk of BEING diseased
- ie do not know if disease or exposure was first
The ratio of
- prevalence of disease in exposed animals
~~--~~ to
- prevalence of disease in unexposed animals
Range
- 0 to infinity
PR = 1
- there is not an association
PR > 1
- there is a risk factor
PR < 1
- there is a protective factor
Note
- 1 MUST BE EXCLUDED from the 95% Confidence Interval for there to be a Significant risk or protective factor - IMPORTANCE OF ASSOCIATION
-
To measure the effect of a factor
Determine
- Attributable Risk
- Population Attribuatable Risk
- Attributable Cause (aka etiologic) Proportion among the exposed
- Population Attributable Proportion - ATTRIBUTABLE RISK
-
AR
Additional risk of disease following exposure compared to that experienced by animals that are not exposed
AR = Iexposed - Iunexposed - POPULATION ATTRIBUTABLE RISK
-
PAR
Proportion of exposed within population times Attributable Risk
PAP = (exposed/n) x AR - ATTRIBUTABLE PROPORTION
-
AP
Proportion of disease in the exposed animals due to exposure
AP
= (RR-1)/RR
= (OR-1)/OR
= (PR-1)/PR - POPULATION ATTRIBUTABLE PROPORTION
-
AP
Proportion of disease in the population due to exposure
PAP = (proportion of exposed that are diseased) x AP -
SAMPLING
WHY
OBJECTIVE -
Increase the efficiency of the study
Objective
- to draw a sample which is a TRUE REPRSENTATION of the POPULATION
- tf estimate of population characteristics will have acceptable
~~ precision
~~ accuracy -
SELECTING SUBJECTS
SIX DEFINITIONS -
Target Population
- population at risk
Study Population
- population sampled
- ideally the same as Target Population
~~ allows extrapolation of results
Sampling Frame
- list of all sampling units in population
- ie a census of
~~ each animal
~~ each flock
~~ each farm
Sampling Unit
- each member of the sampling frame
~~ individuals
~~ flocks/herds
~~ farms
Sampling Fraction
- ratio of Sample Size : Study Population
Sample
- number of sampling units selected -
SAMPLING
TWO TYPES -
Non-Probabilty Sampling
- method chosen by investigator
- convenience sampling
- purposeful sampling
~~ ie specific disease
- volunteers
~~ who like Raul to cut off their head
Probability Sampling
- investigator does not chose
- all animals in population have probability of being sampled which is NOT 0 -
PROBABILTY SAMPLING
AIM
5 TYPES -
Obtain estimates of a variable which are as close as possible to the true value for the TARGET POPULATION
Types
- simple random sampling
- systematic sampling
- stratified sampling
- cluster sampling
- multistage sampling - SIMPLE RANDOM SAMPLING
-
Sampling Frame Required
- ie list of individuals for headectomy
Homogeneous Population
Simple to Perform
Easy estimation of
- means
- variances - SYSTEMATIC RANDOM SAMPLING
-
Do NOT have Sampling Frame
Units are selected at regular intervals from STUDY POPULATION
- ie every third animal through gate
Constan of sampling must not be related to the phenomenon under measurement - STRATIFIED RANDOM SMPLING
-
Population is heterogeneous concerning the variable of interest
Sampling frame divided into Strata befor selection
More precise estimates
Determine a PRIORI to which Stratum each element belongs
ie Two breeds of beef cows
- divide into breed groups
- randomly select from each breed
- select number from each breed that is proportional to representation in population - CLUSTER SAMPLING
-
Sampling Frame is UNKNOWN
- but list of clusters is available
Clusters are randomly selected
- all animals from the selected clusters are sampled
ie Know the sows but not the piglets
- randomly select sows
- sample all piglets of selected sows - MULTISTATE SAMPLING
-
Large and Spread Populations
Complex Method
- more than one sampling frame
- but no sampling frame for units of interest
Not all animals within a cluster are selected
ie sample x piglets from y randomly selected sows -
PROBABILITY SAMPLING
SOURCES OF ERROR
TWO TYPES
WHAT TO DO ABOUT IT -
SAMPLING ERROR aka Random Error
- insufficenct precision around true value
- increase sample size
- change tha sampling procedure
SYSTEMATIC ERRORS aka Bias
- image of reality which diverges from truth
Selection Bias
- non random selection
- non inclusion
- non response
Meaurement Bias
- inaccurate measurements
~~ lack of Se and or Sp
- quality of samples taken
- poorly designed questionairs
Observational Bias
- response error
Confounding Bias
- existance of confounders
- inapporopriate choice of statistical techniques
tf change study design - HEALTH
-
Heath is the state of complete physical, mental and social well-bieng and not merely the absence of disease or infirmaty
or for the large animal types
Average Productin -
PUBLIC HEALTH
7 CONTRIBUTORS -
The Glorious Vets
- Agriculture
- Animal Health and Productin
- Food Industry
- Educations
Others
- Housing
- Public Works
- Communication - VETERINARY PUBLIC HEALTH
-
A component of public health activities devoted to the application of professional veterinary skills, knowledge and resources for the protection and improvement of human health
The contribution to the complete pyysical, mental and social well being of humans through an understanding and application of veterinry medical science -
VETERINARY PUBLIC HEALTH
WHY -
Out of 1415 species of infectious organisms known to be pathogenic to humans
- 61% are Zoonotic
- 75% of emerging pathogens are Zoonotic -
VETERINARY PUBLIC HEALTH
3 DISEASE TYPES -
Endemic Disease
- rabies
- brucellosis
Re-Emerging Diseases
- influenza
- leptospriosis
- salmonellosis
- AI our favorite
New Diseases
- BSE
- SARS -
VETERINARY PUBLIC HEALTH
4 ACTIVITES INVOLVING
DIAGNOSIS
SURVEILLANCE
CONTROL
ERADICATION -
Human protection from animal diseases ie Zoonoses
- an infectious disease transmissible under natural conditions between vertebrate animals an human beings
Food protection and safety
- to ensure the safety of all foods throoughout the process rom production, proccessing, storage and distribution to the consumtion
Emerging diseases and Antimicrobial Resistance
- infections that have newly appeared in the population
- existing infections that are rapidly increasing in incidence or geographic range
Environmental Hygiene
- study and control of the impact of animal populations on environmental health -
VETERINARY PUBLIC HEALTH
3 OTHER ACTIVITES -
Biomedical Models
- diagnostic and therapeutic techniques developed in animals
Disaster Response
- diseases emerge from animals
Bioterrorism
- mainly agent that affect food production
- agents that could pass to humans through food -
VETERINARY PUBLIC HEALTH
6 METHODS -
Epidemiology of Course
- preventative in nature
- population based
Descriptive Epidemiology
Analytical Epidemiology
- epidemiological studies
- development of models
Evaluation of diagnostic tests
Disease monitoring and surveillance
Animal health and economics -
FOOD SAFETY
2 FACTOIDS -
With increasing global consumption of animal derived foods there is an increased poterntial for zoonotic foodborne pathogens, including theri resistance to antibiotics, to disseminate worldwide
There are examples of positive correlations between the levels of foodborne pathogens in food animals and the incidence of foodborne illness in humans
- ie Denmark
~~~~~~ less salmonella in prodcution chickens results in less salmonelloses in humans -
FOOD PROTECTION
DEFINITION - To ensure the safety of all fodds throughout the process from production, porcessing, storage and distribution to consumption
-
FOOD PROTECTION
4 THREATS -
Presence of infectious agents in food
Toxic substance
- chemicals
- pesticides
- residues
- dioxins
- micotoxins
- food additives
Drug and Antibiotic Residues
Novel Foods
- GMO -
FOODBORNE DISEASES
DEFINITION
4 FACTOIDS -
Disease, usually either infectious or toxic in nature, caused by agents that enter the body through the ingestion of food
2.1 million people died from diarrhoeal diseases in 2001
- majority attributable to contamination of food and water
30% of people are suffering from foodborne diseases each year in INDUSTRIALIZED COUNTRIES
USA
- > 250 different diseases have been linked to contaminated food or drink
- Anually
~~~- 80 million cases
~~~- 325000 hospitalizations
~~~- 5000 deaths
Outbreaks may take on massive proportions
- 1994 ice cream salmonellosis strikes 224k USA
- 1988 Clams hepatitis A 300k China -
FOODBORNE DISEASE
LIST 7 TYPES -
Bacterial
Viral
Parasitic
Prions
Naturally occuring toxins
- mycotoxins
- marine biotoxins
- cyanogenic glycosides
- mushroom toxins
Pesisten Organic Pollutants aka POPs
- accumulated in environment
- accumulate in those that lord it over the top of the food chain
- dioxins
- PCBs
Metals
- lead
- mercury
- cadmium -
FOOD PROTECTION
5 STAGES -
Preharvest
- Farm or Field
Post Harvest
- Havest or Slaughter
- Processing
- Ratail or Food Service
- Consumer -
PREHAVEST FOOD SAFETY
WHAT IS IT
WHAT DOES IT CONTROL - 4
WHAT IS IT BASED ON - 4 -
Primarily focused on the protection of Human Health
- considered in the context of a farm to table food
- animal health is a secondary consequence
Controls
- infectious agents
- chemical residues
- drug residues
- pollutants
Based On
- good animal management proctices
- biosecurity practices
~~ ie farm sanitation
- feed selection
- animal testing and elimination
~~ surveillance -
PRE HARVEST FOOD SAFETY
4 BENEFITS -
Prevention of zoonotic human diseases
Control of animal diseases
- including those not pathogenic to production animals
~~~~ Ecoli
~~~~ Salmonella
Animal Welfare
Avoid Litigation -
POST HARVEST FOOD SAFETY
CONTROL FOR 3
BASED ON 4 -
SECONDARY PREVENTION
Control and Prevention of
- sources of pathogens
- food contamination
- adulteration
Based On
- elimination of diseased or contaminated
~~~- meat
~~~- fish
~~~- milk
~~~- eggs
- Prevention of sale of objectionable animal food products
- maintaining strict hygiene during processing
- ensuring proper labelling -
POST HARVEST FOOD SAFETY
SIX BENEFITS -
Prevention of foodborne diseases
- main goal
Control of animal disease
- surveillance
Information regarding causes of condemnation
- prevention
Increased markentability of products
- reduce trade barriers
Consumer Confidence
- perception of safety
Inproving production efficiency
- animal selection -
POST HARVEST FOOD SAFETY
3 LOCATIONS
10 ACTIVITIES -
Location
- abattoirs
- porcessing plants
- retailers
Activites
- evaluation and monitoring of manufacturing practices
- inspection of processing equipment
- verification of produc formulation
- verification of labels
- issuing export certificates
- enforcing licensing
- verifying accuracy of industry grading
- evaluating sanitation procedures
- inspection of final products
- control andimplementation of in plant quality management programs -
EMERGING INFECTIOUS DISEASES
WHAT ARE THEY -
Infections that
- have newly appeared in the population
- have existed but are rapidly increasing in incidence or geographic range -
EMERGING INFECTIOUS DISEASES
6 SPECIFIC TYPES -
Actually a NEW disease
New to Country or Region
Has re-emerged
- after extinction
- after latency
- re introduction via new predisposing factors
Was always there but not DIAGNOSTICALLY proven
- neosporosis
Agent is now different
- mutation
- replacement after vaccination
- ie AI or antimicrobial resistance
New PUBLIC PERCEPTIONS produce new fears
- creates fear of a previously known disease
~~ ie txoplasmosis
~~~~ 50% of people infected in Europe
~~~~ no big deal until you get AIDS -
EMERGING INFECTIOUS DISEASES
2 STEPS -
Introduction of the agent into a new (susceptable) host population
Establisment and futher dissemination within the new host population
Factors that promote one or both these steps will tend to precipitate dieseas emergence -
EMERGING INFECTIOUS DISEASES
2 FACTS
ONE COOL PHRASE -
Numerous examples originating as Zoonoses
- SARS
- Hantavirus
Most appear to be caused by pahtogens already present in the environment
tf Emergence is due to MICROBIAL TRAFFIC -
EMERGING INFECTIOUS DISEASES
MICROBIAL TRAFFIC
7 WAYS HUMANS INCREASE IT -
Movement of people and animals
Ecotourism
Unusual eating habits
- fast food has high amount of industrial processing
~~~~ tf many opportunities for our little friends
Use of Exotic Animals as pets
- lets buy Roul a Gambian Rat
New Laboratory processing techniques
Genetic modifications
- porcine stress syndrome
Misuse
- antibiotics
- antimicrobial drugs -
EMERGING INFECTIOUS DISEASES
MICROBIAL TRAFFIC
3 NATURAL INCREASERS -
Heavy rains and flooding
Natural climate changes
Earthquakes
etc -
ZOONOSES
NAME 10 -
Avian Influenza
- poulty
BSE
- cattle
Lyme Disease
- deer
Hantavirus
- mice
Rabies
- skunks, raccoons
Salmonellosis
- poultry, reptiles
Leistmaniasis
- dogs
West Nile Virus
- birds
Toxoplasmosis
- cats -
ZOONOSIS
6 DEFINITIONS -
Any disease and/or INFECTION which is naturally transmissible form animals
- ie may not be disease in animal
AGENTS of which are transmitted between vertebrate animals and people
- agents not vectors
An infectious disease transmissible under natural conditions between vertebrate animals and human beings
- can go both ways
Zoonotic agents are infectious agents which are not only confined to one host, but which can cause an infection, with or without clincal disease , in several hosts including humans -
ZOONOSIS
3 NOTS -
Same infectious agent can infect humans and animals but there is NO TRANSMISSION between animals and humans
- clostridium tetanus
Infectious agent is strictly transmitted between humans
- chicken pox virus
Infectious agent is striclty transmitted between animals -
ZOONOSIS
4 FACTIODS -
75% of emerging diseases are zoonoses
45% of reportable human diseases in California are zoonoses
50% of population in South America get infected at least once with zoonotic pathogen
More thatn 200 zoonoses currently cause a wide variety of human illness -
ZOONOSES
3 REASONS TO CARE -
Imapct on Health
- medical assistance for humans and animals
Impact on Economy
- losses of animals adn animal products
- loss of production
Social Impact
- decrease of human production
- rehabilition of sick
- worries
- death -
ZOONOSES
7 AGENT CLASSIFICATIONS -
Parasitic
- toxoplasmosis
Bacterial
- campylobacteriosis
Viral
- rabies
Fungal
- ringworm
Spirochaetal
- leptospirosis
Rickettsial
- Q fever
Prion
- BSE -
USUAL RESERVOIR HOSTS
4 CLASSIFICATIONS -
Direct Zoonosis
- Host
~~~~ single vetebrate animal species
- rabies
- brucellosis
Cyclozoonosis
- host
~~~~ two vertebrate animal species
~~~~ ie one sheds, one eats
Metaxoonosis
- Host
~~~~ vertebrate animal species and an invertebrate animal species
- ie vector borne
Saprozoonosis
- Host
~~~~ vertebrate animal species and a Non-Animate developmental site
- ie host sheds eggs which must spend time in environment to become infective -
TRANSMISSION PATTERNS
3 CLASSIFICATIONS -
Anthropoxoonosis
- Maintenance Cycle
~~~~ animal to animal
- Zoonotic Cycle
~~~~ animal to human
- rabies
Zooanthroponosis
- Maintenance Cycle
~~~~ human to human
- Zoonotic Cycle
~~~~ human to animal
- human tuberculosis
Amphixenosissis
- Maintenance Cycle
~~~~ animal to animal
~~~~ human to human
- Zoonotic Cycle
~~~~ animal to human
~~~~ human to animal
- stphylococcosis
- influenza - REVERSE ZOONOSES
- Diseases of people occasionally transferred to animals and then transferred back to people
-
TRANSMISSION FROM ANIMALS TO HUMANS
6 TYPES -
Heirloom
- ancient origin
- agents transferred from prehisoric animals to early primates
- NOT Zoonoses
Direct
- animal to human
- no human to human
Indirect
- ie via food
Vector
- animal reservoir
- very rarely human to human
Animal to Human to Human
Now Human to Human Only
- orignially zoonoses
- now ciculates only in humans
- NOT Zoonose -
ZOONOTIC DISEASES
FREQUENCY AND PATTERN
6 INFLUENCES -
Nature and Extendt of human animal contacts
- pets in developed world
Socioeconomic Conditions
- contaminated water and food in developing world
Religious Belief and Cultrual Influences
- ie not eating certain species
Climate and Environmetal Disasters
Anima and Human Population Movements
- travel times are much shorter than most incubation periods
Animal Management
- intensive farming
- waste disposal
- enviromental contamination
- increased stress results in increased shedding -
ZOONOTIC TRANSMISSION
5 WAYS INDUSTRIAL SOCIETIES FACILLITATE -
Leisure time acitivies
- outdoor recreation
Ownership of pets
- love those gambian rats
Poor Personal Hygiene
Suburban Development
- intrudes on indigenous animal population
- revenge of bambi
Intensive animal production -
ZOONOSES
8 RISK GROUPS -
Agriculture
Animal product processing and namufacture
Forestry and Outdoors
Reacreation
- pets
- wild animals
Public Health Professionals
Emergency
- ie refugee camps
- loss of sanitary infrastructure
Innunosupressed Individuals -
URBAN ZOONOSES
5 PATTERNS -
Centripetal Trend
Pets and Exotic animals
Non-professional diseases
Children
Indirect economic losses -
SYLVATIC ZOONOSES
5 PATTERNS -
aka natural
Centrifugal trend
Food and Work animals
Professional Diseases
Adults
Direct economic losses -
ZOONOSES
DIRECT CONTACT
PREVENTION AREAS 3 -
Application of basic biosecurity measures
- hand washing
~~~~ especially after handling sick animals
- treatment
~~~~ skin abrasions
~~~~ gastro intestinal diseases
- disinfection of infected premises
- change of clothing and boots between premises
Control Diseases and Risk Factors
- treatment of primary condition in animals
- rodent control
- risk factors associated with food borne diseases
Indirect beefirt of on farm food safety programs -
ZOONOSES IN CANADA
3 SOURCES OF INFECTION -
Direct contact with animals
- ingestion
- skin
- mucosa
- respiratory tract
Indirect Contact
- infected person
- environmental contamination
~~~~ water
~~~~ soil
~~~~ vegetables
- leisure activites
Foodborne Diseases
- salmonella swine and poultry
- compylobacter jejuni poultry
- Ecoli O157:H7 and VTEC cattle -
SALMONELLOSIS
6 FACTOIDS -
Disease caused by a groopu of bacteria called Salmonella
Agent is very common in environment
Disease produced usually varies with the SEROTYPE of Salmonella involved
Around 2300 different seortypes
Most Salmonella serotypes are pathogenic for humans
Worldwide Distribution -
SALMONELLA SPP
NATURE OF THE BEAST
FOR 6 POINTS -
Freezing does not kill
Grows
~~ 7 to 47 deg C
~~ pH 4 to 9.5
Survival
- long periods in food and manure
Easily DESTROYED BY HEATING
Sources of Infection
- infected animals contaminate
~~~~ feed
~~~~ water
~~~~ soil
Route of infection
- oral -
SALMONELLOSIS
IN ANIMALS -
Salmonella spp cann infect both warm and cold blooded animals
- 94% of reptiles infected
Diseases caused
- Diarrhea
~~~~ most common
~~~~ via S. typhimurium
- septicemia
~~~~ S. choeraesuis in pigs
- abortions
~~~~ S. abortusvois in sheep -
SALMONELLOSIS
COMMON SEROTYPES
CATTLE -
S. typhimurium
S. dublin
S. newport -
SALMONELLOSIS
COMMON SEROTYPES
SHEEP -
S. typhimurium
S. dublin
S. anatum
S. montevideo
S. abortusovis -
SALMONELLOSIS
COMMON SEROTYPES
SWINE -
S. typhimurium
S. choleraesuis
- most pathogenic -
SALMONELLOSIS
COMMON SEROTYPES
HORSES -
S. typhimurium
S. anatum
S. newport
S. enteritidis
S. arizonae -
SALMONELLOSIS
COMMON SEROTYPES
AVIAN -
S. pullorum
S. gallinarum
S. typhimurium
S. enteritidis
S. heidelberg -
SALMONELLOSIS
IN ANIMALS
CARRIERS
3 TYPES -
Active
- infected, recently or reactivation
- shed bacteria
- can kill young chickens
Silent
- cleared the bacteria in GIT but the bacteria is still present in lymph nodes
- shed if stressed
Passive
- salmonella is present in feces without infection
- negative if removed from contaminated environment
- ie injested but not infective
Note
A positive herd can remain positive for decades -
SALMONELLOSIS
DISTRIBUTION -
Mainly Poultry and Swine
Less common in Cattle -
SALMONELLOSIS
IN HUMANS -
Food Sources
- drinking water
- milk and dairy products
- raw meats and poultry
- eggs
- fish
- shrimp
- frog legs
- cream filled deserts
- fruit and vegetables
Direct contact
- 10% of dogs carry
- 1 - 27% of cats carry
4 million infections annually
500 deaths annually -
SALMONELLOSIS
IN HUMANS
7 FACTIODS -
Under Reported
Acute Symptoms
- nausea
- vomiting
- abdominal cramps
- diarrhea
- fever
- headache
Chronic Consecquences
- arthritic sypmtoms 3- 4 weeks after acute symptoms
Incubation Period
- 6 - 48 hours
- short tf easy to trace source of infection
Infective Dose
- 10k to 1M
Duration of Sysmptoms
- 1 to 2 days
- may be prolonged
~~~~ host factors
~~~~ ingested dose
~~~~ strain charcteristics
Cause of Disease
- penetration and passage of Salmonella organisms from GIT lumen into epithelium of SI
- producing inflammantion -
SALMONELLOSIS
ON FARM PREVENTION
9 STEPS -
Closed Herds or Flocks
Keep animals in small groups
Scrutinize purchased animals
Sterilize feed ingredients
Provide clean drinking water
- housed animals
- grazing animals
Pervent access of wild birds and rodents
Thoroughly cleanse and disinfect housing between batches
Monitor poultry breeding stock
- remove excretors
Disinfect hatching eggs and fumigate incubators -
SALMONELLOSIS
KITCHEN CARES 9 -
Keep eggs refigerated
- no incubation < 4 deg
Throw out cracked or dirty eggs
Wash hands and cooking utensils after they have been used with eggs
Do not keep eggs warm for more than 2 hours
Refigerate leftover foods containing eggs quickly
Avoid eating raw eggs
Always cook meat and poultry
Cook stuffing separate from meat
Drink only pasteurized Milk and Juice -
COLIBACILLOSIS
FACTOIDS 5 -
Bacterial disease caused by Echerichia coli
Normally found in the intestines of warm blooded animals
Over 200 serotypes
- most harmless
Different grops of E. coli cause gastroenteritis in humans
- Entertoxigenic ETEC
- Enterpathogenic EPEC
- Eneroinvasive EIEC
Most important in Canada
- Verotoxin producing E.coli VTEC
- O157:H7
- recognized in 1982 as cause of illness -
E COLI O157:H7
5 LIFESYLE FACTS -
Survies
- refrigeration
- freezing
- low pH
Low doses produce infection in ALL people
DESTROYED BY HEATING
Route of infection
- oroal
Sources of Infection
- food
~~~~ ground beef products
~~~~ raw milk
~~~~ apple juice
~~~~ alfalfa sprouts
~~~~ cole slaw
- water -
E COLI O157:H7
IN ANIMALS
6 FACTOIDS -
Once colonize shedding is short
- < 30 days
Animals undergoing nutritional stress are more likely to shed
- fasting may increase shedding
There is some suggestion that warmer environments increases shedding
Higher risk of shedding in younger calves
Shedding signifiicantly associated with weaning
Shedding has NOT been associated with CLINICAL symptoms ins cows
- tf silent carriers -
E COLI O157:H7
IN ANIMALS
PREVALENCE -
Cattle
- 43% VTEC
- 7.5% O157:H7
Poulty
- none
Swine
- 20% VTEC but non pathogenic -
E COLI O157:H7
IN HUMANSS -
Declining
Infective Dose
- 10 to 200
- extremely low
Incubation Period
- 3 to 8 days
- more difficult to trace back source of infection
Symptoms
- sever abdominal cramps
- watery diarrhea
- bloody diarrhea
- vomiting and nausea
- low grade fever
Complications
- hemolytic uremic syndrome
- kidney failure
- blood clotting disorders
- anemia
- CNS disease -
E COLI O157:H7
ON FARM PREVENTION
6 PLANS -
Note
- Not Epidemiologically Understood tf just try to prevent transmission
Seperate feed from mamure
Prevent water tank contamination
Decrease hide contamination
Transition diet modification
- reduce shedding
Continue investigation of shedding patterns in cattle
Reduce burden in GIT
- vaccination -
E COLI O157:H7
FOOD PREVENTION
EIGHT EFFORTS -
Note
- low infective dose
- tf assume all food contaminated
Never
- thaw food on counter
- let sit out of refrigerator > 2 hours
Use
- refrigerated ground meat within 3 to 4 days
- frozen gound meat within 3 to 4 months
Wash hands utensils and work areas after contact with raw meat
All meat, poultry and fish should be well cooked
- > 71 deg C
Nerve allow raw foods to contact
- ready to eat foods
- utensils and dishes
- serving plates
Wash all fresh fruits and vegetables thoroughly before consumption
Immunocompromised populuation should avoid consuming
- unpasteurized juice
- raw sprouts
- raw or partially cook meats
Follow the Rules of Hygiene
- hand washing - CAMPYLOBACTERIOSIS
-
Bacterial disease caused by genus Campylobacter
Main Serotypes responsible for human disease
- Compylobacter jejuni
~~~~ major source >90% of human disease
- Campylobacter coli
- Campylobacter lari
Geographic Distribution
- worldwide -
CAMPLYLOBACTER SPP
LIFESYLE 7 -
Optimum growth 42 deg C
- bird temp
- will not grow below 30 deg C
- will not mutiply on chilled food but survives
~~~~ SURVIVES BETTER INSIDE REFIGERATOR THAN IN ENVIRONMENT
Likes Acid Environment
- ph 4.9
Salt Sensitive
- >2% inhibits
Does not survive well in food processing environments
Route of Infection
- oral
Sources of Infection
- poultry
- birds
- cattle
- household pets
Antibiotic Resistance
- especially Quinalones -
CAMPYLOBACTERIOSOSIS
IN SWINE -
Most herds infected with C.coli
- but without disease
- C. coli responsible for < 5% of human cases
High prevalence of C. jejuni in USofA
- role in human cases -
CAMPYLOBACTERIOSOSIS
IN CATTLE -
C. jejuni
- 40 to 80% of cattle
- 80% of farms
C. coli
- 20% of cattle
Gastrointestinal Disease
- C. jejuni
Venereal Disease
- C. jejuni
- reduced fertility in bulls and cows
- abortions
Most Human outbreaks associated with raw milk -
CAMPYLOBACTERIOSOSIS
IN BROILERS -
Asymptomatic
- silent carriers
C. Jejuni
- 40% of flocks in Denmark
- 35 to 80% broilers and retail chicken in Alberta -
CAMPYLOBACTERIOSOSIS
IN SHEEP - Abortions
-
CAMPYLOBACTERIOSOSIS
IN HUMANS -
Most common diarrheal disease
Infective Dose
- minimum 400
Incubation period
- 2 to 5 days
Asymptomatic
- usually
Enteritis
- diarrhea
- fever
- mild cramps
- self limiting in 95% of cases
- Duration 1 week
- infectious dose 10k
Extraintestinal Infections
- bactermia in 1 in 1000 cases
- Arthritis
- brusitis
meningitis
- Guillain-Barre syndrome
Emergence of Antibiotic Resitannt strains
- quinolones -
CAMPYLOBACTEROSIS
PREVENTION ON FARM 4
WHY IS IT DIFFICULT -
Difficult because of large bird reservoir
Avoid horizontal transmission from environment to bird flocks
- via strict hygeine in closed housing
Use chlorinated water
Immunization of older birds
No viable methods for reduction of campylobacter on cattle farms -
CAMPYLOBACTERIOSIS
PREVENTION FOOD -
Wrap fresh meats in plastic bags at the market to prevent blood from dripping on other foods
Refrigerate foods promptly
Cutting boards and counter used for food preparation should be washed immedialtely after use
Avoid eating raw or undercooked meats
Avoid eating raw eggs or foods containing raw eggs
Avoid drinking raw milk
Handwashing befor and after food preparation
Hand washing after handling pets - WHAT DO ALL VETS HAVE IN COMMON
- Involvement in Public Health
-
VETERINARY INFRASTRUCTURE
ROLE -
Pivitol
Veterinary infrastructure of a country is an important NEGOTIATING TOOL in International Trade -
UPSTREAM
DOWNSTREAM -
Better to find out why more bodies are falling in the river than to build a better rescue and recovery system
ie Take care of the problem during
- Food Production
- Food Processing
- tf hire more vets -
PREVENTION
3 STAGES -
Primary
- Susceptability Stage
- lower risk of exposure
- lower consequence of exposure
- ie vaccination program
Seconday
- Subclincal Stage
- Early Detection
- Prompt Intervention
- ie Pen Riders in Feedlot
Tertiary
- Clincal Disease
- Recovery
- Death -
FOOD SAFETY
PRE-HARVEST -
All activities aimed at protecting the health of the food animals while they are on the farm
- Herd health programs
- individual animal medicine
- prevent or reduce
~~ infectious
~~ parasitic
~~ chemical
~~ physical harm
Goal is to establis complete balance between
- Host Factors
- Agent Factors
- Enviromental Factors
By directly protecting the health of animals by reducing disease, we are supplying healthy animals to the food chand and performing and importan food safety activity
- Glorious but what about infectious agents that are pathogenic to people but do not cause disease in animals
~~ Ecoli O157:H7
~~ salmonella -
FOOD SAFETY
PRE HARVEST
PRODUCER GROUPS -
Goal science Based Practices which are DEFENSIBLE to the Global Community
- Absence of Evidence is NOT Evidence of Absence
Developing New Codes of Practice
- voluntary
Developing On Farm Food Safety Programs
Problem Based Research -
ON FARM FOOD SAFETY PROGRAM
DEFINITION
BENEFITS 3 -
A comprehensive plan to reduce foodborne illness through a variety of interventions
Benefits
- Maintaining or expanding international trade
- increased management effectiveness and cost saving
- increased consumer confidence -
ON FARM FOOD SAFETY PROGRAM
HOW
WHAT -
Farmer organizations recognized increased demands made by retailers and consumers
Proactive
- farmer driven
- farmer friendly
Flexible
- can be adapted
Commodity Based
- specific to production species
Based on HACCP-like Principles
- Hazard Analysis and Critical Control Points
Not about doing something different, more about writing down what you do
- Write what you do
- Do what you write -
ON FARM FOOD SAFETY PROGRAM
WHAT IS THE DIFFERENCE
BETWEEN FARMERS AND PUPPIES -
Puppies are CUTE when the whine
sorry this whole thing is starting to look like a sunshine enema... -
ON FARM FOOD SAFETY PROGRAM
4 STEPS TO SUCCESS -
Committed operator and well trained staff
- people have to believe in the value of the program
Assessing the hazards
Identifying
- Good Management Practices (GMPs)
- Critical Control Points (CCPs)
- enable control or elimination of hazards
Implementing the plan and documenting actions -
FOOD SAFTEY HAZARDS
IDENTIFY 3 -
Physical
- broken needles
Chemical
- drug residues
- toxicities
- poisonings
Biological
- bacterial
- viral
- parasitic
- prions -
ON FARM FOOD SAFETY PROGRAM
HAZARDS
CANT LIVE WITH THEM
CANT LIVE WITHOUT THEM -
Some hazards CAN be controlled, reduced or eliminated
- Antimicrobial Residue
~~ call GFaRAD
- broken needles
~~ indentify
~~ segregate
~~ communicate
Some hazards CANT easily be controlled, reduced or eliminated
- bacteria that do not harm the animal but are pathogenic to humans
- cmpylobacter
- salmonella
- Ecoli O157:H7 -
GOOD MANAGEMENT PRACTICES
WHAT
KEY ELEMENTS 9 -
aka GMPs
Based on Good Production Practices and Standard Operating Procedures (SOPs)
Key Elements of GMPs
- Animal Handling
- Indentifying health problems
- Pharmaceutical practices
- Premise and Equipment
- Maintenance
- sanitation
- Cleaning and Disinfection
- Waste Disposal
- record Keeping -
GOOD MANAGEMENT PRACTICES
BIOLOGICAL HAZARDS
EXAMPLES 5 -
Controlling Access
Cleaning
- all in all out
Shipping clean animals and birds
- ie poultry flock sheets
~~ verify feed withdrawel times to facillitate empty GIT
~~~~ tf lower contamination
Medications and Vaccines
- proper disposal of dead or diseased animals
Minimize Stress
- increased stress = increased shedding
- ie stage closer to shipping areas
- adequate space
- good handling facilities
~~ injury prevention -
STANDARD OPERATING PROCEDURES
WHAT ARE THEY
2 EXAMPLES
WHAT DO THEY REQUIRE -
Step by Step Procedures
Vaccination SOPs
- vaccine protocol
- what vaccine
- when
- for which animals
Clinical Disease SOPs
- frequency of inspection
- what to do when sick identified
- how to treat
Requires Training of Personel -
FOOD SAFETY RESEARCH
ON FARM
WHY -
As food industry works through processes it will continue to indentify areas where there are
- GAPS in KNOWLEDGE
- fancy that
GAPs
- ie Camplyobacter jejuni
~~ high in Poultry and also Hogs
~~ human sources of infection not actually identified
- ie did Johnny get his nasty Ecoli infection from
~~ the goat at the petting zoo
~~ or the burger on the way there
Developing therapies for reduction of comensual infection in food animals by agnets pathogenic to humans
- ie probiotics to reduce Ecoli in beef cattle
- vaccinations
- lytic phage therapy
- therapies must be acceptable to producers and consumers -
FOOD SAFETY
PRE HARVEST
VETERINARIANS ROLE
SUMMARY 5 POINTS -
Keep doing what we do best
- desingningand implementing herd health programs
- treating individuals animals
Education in herd health and management to help producers make sound decisions
Applied Research
Auditors of ON Farm Food Safety Programs
- currently raising awareness
- regulatory component not yet identified
~~ will involve vets -
INFECTIOUS HUMAN MORTALITY
TOP 5 SOURCES -
Account for 85%
Diarrheal Disese
- food
- water
Measles
Mumps
AIDS
Malaria
TB
- food sourced
tf 2 of Top 5 Food Borne -
FOOD BORNE ILLNESS
6 STUPENOUS STATISTICS -
USofA?
- 1 in 4 affected annually
- 7.6 M cases/year
- 32 K hospitalizations
- 500 Deaths
World Wide
- 1.6 B cases/year
- 2.1 M deaths/yeare
tf Eating is RISK BEHAVIOR in most parts of world -
CFIA'S MANDATE
3 PILLARS -
Safe Food
Consumer Protection
Market Access -
CANADIAN FOOD SAFETY SYSTEM
3 PRINCIPLES -
Heatlh of the population must remain Paramount
Policy decisions must be based on Scientific Evidence
All sectors and jurisdictions must collaborate to protect consumers -
FOOD BORNE DISEASE
WHO DEFINITION -
Any disease of an infectious or toxic nature caused by or thought ot be caused by the consumption of Food or Water
Occurs when there has been a failure to adequately control the hygeine and temperture of the WHOLE food chain -
MEAT INSPECTION PROGRAM
WHEN
WHAT
WHO -
National Meat Inspection
- founded 1907
- response to human TB
- manily aquired from cattle
- not practicle to test cattle
~~ tf inspect carcasses in central location
Ensures that meat and poultry products are safe and wholesome
Involved in
- Federal Plants
- Domestic Plants
~~ licensed by Province -
FEDERAL PLANTS
VETERINARY INVOLVEMENT
8 WAYS -
Humane Transport
- animal health
- animal advocate
Antemortem and Postmortem Dispositions
- public health
- animal health
Sanitation
- public health
Sampling and Testing
- disease surveillence
- public health
- animal health
Labeling
- weight fraud
- allergies via ingredients
- public health
Imports
- public health
Exports
- Economic
- must be licensed to export
Auditing
- conformation to procedure
- public health -
VETERINARY MEAT INSPECTION
5 WHYS -
Sound, safe, non-adulterated, correctly labeled meat products
- public health
Identify Disease in flocks and herds
- animal health
- public health
Collect data on disease occurence in animals
- report to OIE re Country Status
- animal health
Prevent introduction of exotic animal diseases
- animal health
- public health
Provide produces and operators with Export outlets
- economic -
FOOD BORNE DISEASE
2 TYPES -
Most are Bacterial
Infection
- living organisms
- takes time for illness to develop
- ie Listeria Monocytogenes
~~ 21 days for symptoms
~~ hard to investigate
Intoxication
- Preformed toxins from bacterial
- symptoms develop rapidly
- 6 to 8 hrs or less -
FOOD BORNE DISEASE
SOURCES 3 -
Directly form animals
- salmonella
- camplyobacter
- E.coli
Environemtal
- Clostridia
- Listeria
- Bacillus
Human Reservoir
- staphylococcus
- viruses
~~ ie Norwalk like on cruise ships -
FOOD BORNE DISEASE
TRANSITION -
VISIBLE TO INVISIBLE
Historically
- food, meat or milk carried pathogen
Currently
- contamination during or subsequent to production
- often part of Normal Intestinal Flora of animals
~~ tf not clinical disease to animal
Identification of Infection
- challenging
- requires more education -
CONSUMER DEMANDS
CHANGE -
Post WWII
- just wanted Cheap Meat
Currently
- demand for guaranteed, wholesome, environmental and animal welfare friendly product
- concern for residues and genetic modifications -
HACCP
3 BULLETS -
Pervention of potential food safety hazards rather than detection problems in finished product
- driven in '60s by NASA
~~ no cosmotic diarrhea
Based on sound technological nand scientific principles
Indentifies and prioritizes Intervention at Critical Conrol Points (CCPs) -
HACCP
WHO
WHERE -
Plant is responsible for writing and implementing their system effectively
CFIA approves the system and audits it regularly to ensure compliance
Now a Condition of License
Moving towards Farm Based HACCP programs -
HACCP SYSTEM
5 WHATS -
Product Description
- identify end user and tf risks
~~ ie adult vs infant consumer
Plant Schematic
- movement of product and inedibles
- avoid cross contamination
Flow Diagram
Prerequisite Programs
- premises
- transportation
- storage
- equipment
~~ cleaning
~~ calibration ie temperature
- personel
~~ training
~~ hygiene
- sanitation
- pest control
- recalls
- monitoring
- actions
- verification
HACCP Plans
- CCPs -
CRITICAL CONTROL POINTS
DEFINITION -
Any point, step or procedure at which control can be applied and a food sfety hazard can be prevented, eliminated or reduce to an acceptable level
- time at temperature
- refrigeration
- addition of sodium nitrate curing agent
~~ prolongs shelf life
~~ chemical hazard
~~ mixed with salt to avoid over consumption
- metal detection -
ANTIBIOTIC RESISTANCE
HUMAN MEDICINE 3
VETERINARY MEDICINE 3 -
HM
Perscription of Antibiotics for viral infections
Non perscription use
- especially developing world
Incomplete course
VM
Low level use for Growth Promotion
Prophylaxis
Incomplete Course -
ANTIBIOTIC RESISTANCE
CONSISTENT THEMES 7 -
Resistence develops in bacteria when antibiotics are given to animals
Bacteria spread from animals to humans
Some of these bacteria cause disease in humans
Impact of resistance on human health UNKNOWN
- perception of significant problem
Relative contribution of animal or human use not known
Policy changes expected to have negative consequences for agriculture
Issues are complex
- We don't know much -
ANTIBIOTIC RESISTANCE
5 REASONS TO CARE -
More difficult and expensive to prescibe for resistant strains
Resistant strains are more virulent
- tf more severe disease
Increased in number of cases
Enhanced spread of infection or duration of shedding
Cost -
ANTIBIOTIC RESISTANCE
5 ACTIONS -
Surveillance
Education
Infection Control
Reductions in Consumption
Canadian Integrated Program for Antimicrobial Resistance Surveillance (CIPARS) - CIPARS
-
Canadian Integrated Program for Antimicrobial Resistance Surveillance
Nationally Integrated
Information on Antibiotic use
National abattoir project
- enteric
~~ clinical disease in animals
- commensal
~~ animal unaffected
Public health laboratories
- enteric
Provides for monitoring of trends in resistance in animal and human populations
- perception vs reality -
DISEASE CONTROL
NON ANTIMICROBIAL METHODS
7 -
Biosecurity
Quarantine
Vaccination
- prevent rather than treat
Selective Sourcing
All in All out
- disinfect inbetween
Laboratory Testing
- treatment delays
Sanitation
Farm Entry Restrictions - RESIDUES VS RESISTANCE
-
Residues produce Resistance
BUT
Resistance DOES NOT produce residues -
CHEMICAL RESIDUES
DEFINITION -
A substance having pharmacological action, their metabolites and other substances transmitted to animal products and which are likely to be harmful to human health
Requirement to differentiate between safe and unsafe concentrations -
CHEMICAL RESIDUES
7 EXAMPLES -
Antimicrobials
Pesticides
Hormones
beta-agonists
- clymbuteral used in veal calves
~~ remember the murdered Italian vet
Herbicides
Heavy Metals
- contaminated construction materials
Fungicides -
CHEMICAL RESIDUES
3 CONSUMER CONCERNS -
Drug Resistance
Alergies
- ie penecillan residues
Toxicity
- long term consumption -
DRUG RESIDUES
HOW -
Occur due to problems in CLEARANCE RATES
Off Label Use
- overdose
- diferent route
~~ IM vs IQ
- more frequent intervals
- different species
- LIABILITY
~~ cover your ass
Technical Erros
- injection between muscle bellies
- amount per site
~~ < 10 mls
- site choice
~~ neck usually better than butt
INflammatory Reactions
Labelling Errors
- non updated withdrawal times -
CHEMICAL RESIDUES
AND CFIA -
CFIA performs random weekly sampling for antibiotics in plant
Testing for other residues done regularly according ot sampling plan from Ottawa -
FOOD SAFETY
REMEMBER ON THING -
Remember that every food animal you treat is NOT
- a steer
- a pig
- a chicken
It is Someones
- steak
- ham
- drumstick
It could be for someone young, old or immunosuppressed
It could even be yours