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Chapter 10: Haemophilus, Bordetella, and Legionella


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What do Haemophilus, Bordetella, and Legionella have in common?
Gram (-) rods, all acquired through the respiratory tract
What are two important factors in how H.flu causes disease?
Polysaccharide capsule confers virulence. Antibodies to the capsule are lacking in infants and children between 6 months and 3 years of age.
List the diseases that can be caused by H. influenza type b (Hib)?
Acute epiglottitis
Septic arthritis
What is the problem with treating Hib meningitis with antibiotics? Solution?
The release of cellular antigens (like endotoxin) from lysed bacteria results in a violent immune response that can further destroy neurons. Potential solution is treatment with steroids 20 minutes prior to antibx
What are the drugs of choice for serious Hib infections? For less serious infections?
3rd generation cephalosporins.
Ampicillin or amoxicillin.
Which species causes the STD chancroid? Clinical syx?
Haemophilus ducreyi. Painful genital ulcer, unilateral painful swollen inguinal lymph nodes in 50%
What is the diff dx for genital ulcers?
1) Syphilis
2) Herpes
3) Lymphogranuloma venereum (Chlamydia)
4) Haemophilus ducreyi
How is chancroid treated?
Erythromycin or trimethoprim/sulfamethoxazole
What organism causes whooping cough? Where do you see the majority of these cases today?
Bordetella pertussis. Unimmunized infants younger than 1 year and young adults, because the vaccine only provides protection for about 15 years.
List the stages of disease with Bordetella pertussis?
1. 1-week incubation
2. Catarrhal stage ( similar to an upper respiratory tract infection)
3. Paroxysmal stage (Bursts of nonproductive cough, inspiratory gasp, vomiting)
4. Convalescent stage
Describe the WBC profile of whooping cough?
High lymphocytes, only moderate increase in neuts. (looks more like a viral picture)
Describe treatment, prophylaxis for whooping cough?
Primarily supportive. Erythromycin may prevent disease in the early stages. DPT vaccination is effective.
Describe Legionella pneumophila? How does it cause infection?
Aerobic gram-negative rod, ubiquitous in water environments. Aerosolized contaminated water is inhaled. Facultative intraceelular parasite that settles in the lower respiratory tract.
What diseases can Legionella cause?
1. Asymptomatic infection
2. Pontiac fever
3. Legionnaires' disease
Pontiac fever has a clinical profile similar to...?
Describe Legionnaires' disease?
High fevers, severe pneumonia. One of the most common causes of community acquired pneumonia, but rarely diagnosed correctly.
What are the risk groups for Legionnaires' disease? Treatment?
Patients over 50 who are smokers or whose sputum gram stain reveals neutrophils and very few organisms (Legionella is really small). Treat with erythromycin.

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