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MED2042 WEEK 3 - Epidemiology


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What is epidemiology?
The branch of medical science that deals with the study of the causes, distribution and control of diseases in populations.

What is the global disease burden?
- losses from premature death + loss of healthy life resulting from disability
- World Bank - Investing in Health report
Describe the state of infectious diseases in 1900.
- Infectious diseases were the leading cause of death worldwide.
- 30% of all deaths were caused by tuberculosis, diarrhoea and pneumonia
- Average life expectancy was 47
> primarily due to infant and childhood deaths from infectious disease
> a child born in 1900 had a 10% chance of dying between ages 1 and 4 from an infectious disease
- represented an improvement over previous centuries
Describe the state of infectious diseases in 2000.
- Infectious diseases mortatility rate drastically reduced, especially in western countries.
- Deaths primarily resulted from chronic illnesses - heart disease, cancer, stroke
- average life span increased to 76
What are the reservoirs of infection?
What are the modes of transmission of infection?
Direct contact
Food and water
Define Emerging Infections.
An emerging infection is defined as a "new, re-emerging, or drug-resistant infection whose incidence has increased or threatens to increase.
List some of the new infectious agents and diseases (1980-2005).
Legionnaire's disease
Toxic shock syndrome
Lyme disease
E.coli O157:117
Nipah virus
Ebola virus
Avian flu
What are some old diseases that have re-emerged?
Dengue Fever
Yellow Fever
What is a global problem related to emerging infections?
Antimicrobial resistance
What changes has there been in demographics and behaviour?
Changes in population
- increases in susceptible population
> ageing population more susceptible to bacterial infections
> decreased communal immunity from subclinical infection
> immunosuppression resulting from other diseases - may result from improved medical technology (e.g. ICU)

Societal changes
- increased use of day care facilities
- altered sexual behaviour
- intravenous drug use

Movement of people by immigration
What changes has there been in technology and industry?
- Many changes improved health
- Others unexpectedly associated with emergence of disease
> Airconditioning cooling towers - Legionnaire's disease
> super-absorbant tampons - Toxic shock syndrome
> fast food hamburgers - E. coli O157:H7
> use of antimicrobials in animal husbandry - emergence of drug resistant Salmonella and Campylobacter
> changes in rendering and processing animal feed - mad cow disease
What changes has there been in the environment and land use?
- Encroachment on tropical rain forests - emergence of new viral haemorrhagic fevers
- Rapid growth of cities with inadequate infrastructure - inadequate hygiene and sanitation leads to diarrhoea (e.g. cholera)
- altered agricultural practices in developed countries - toxic algal blooms
- conservation of native wildlife - deer in US > lyme disease
- climate change - increased rainfall in SW USA, increased vegetation, increased rodents, increased rodent-human contact > hantavirus
What changes has there been in international travel and commerce?
- dramatic reduction in travel times in twentieth century
- facilitates global transmission of diseases spread by personal contact
> shigellosis
> gonorrhoea
> respiratory infections
> international food borne outbreaks
> hemorrhagic fevers
Describe microbial adaptation and change.
- Microorganisms continue to evolve rapidly in response to changes to thier environment
> direct selective pressure of increased antibiotic use leads to increased antibiotic resistance
- reason for change not always clear
Describe the breakdown of public health measures
- complacency from past successes e.g. tuberculosis
- competing priorities
"infectious diseases are no longer important syndrome"
- economic rationalism
- war, natural catastrophe, civil disturbance
Describe the likely state of emerging infections between 2001-2100.
- As change continues so will the emergence of infectious diseases
- Predictions (Cohen)
> more chronic diseases will be identified as infectious
> food safety will be a major issue as technology changes
> antimicrobial resistance will remain a major problem, an everchanging problem e.g. Linezolid (Zyvox)
What are response strategies for emerging infections?
Center for Disease Control

- enhance surveillance and response capabilities
- encourage applied research
- strenthen public health infrastructure & training
- develop, implement & evaluate strategies for disease prevention and control
Describe Avian Influenza
- Influenza virus
- RNA virus that varies over time
- On the viral coat are two proteins
> hemagglutinin (16)
> Neuraminidase (9)
- These can combine in different combinations in different viruses
- Human viruses (H1N1, H1N2, H3N2)
- One particular form of avian flue (H5N1) appears very pathogenic
- Infects domestic and wild bird populations including migratory birds
- H5N1 is currently quite widespread in many Asian countries - China, Thailand, Cambodia, Vietnam, Indonesia, South Korea
- Has spread to humans with 30-50% fatality rate
- Has rarely spread from person to person and seems currently limited to one transmission
- What if it recombines to gain better person to person tranmission

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