L41 Typhoid fever

Question 1

Typhoid fever is caused by which organism?

Answer 1

Salmonella typhi

Subspecies: S.enterica subspecies enterica

Question 2

Which of the following about Salmonella species is correct?
A. It is motile
B. It is Gram -ve 
C. It is a bacilli 
D. It belongs to Enterobacteriaceae
E. It has more than 2500 serotypes

Answer 2

All of the above

Question 3

What are the 3 antigens in S.typhi?

Answer 3

1. O antigen: somatic, cell surface carbohydrate (O9-O12)
2. H antigen: flagella/motility
3. Vi antigen: virulent capsular antigen

Question 4

Human is the only host for S. typhi. What is the route of transmission of S. typhi?

Answer 4

Faecal-oral route - contaminated water/food

Question 5

What is the risk factor for Typhoid fever?

Answer 5

Achlorhydria (insufficient gastric acid production)

Question 6

What is the pathogenesis of typhoid fever?

Answer 6

1. Invade via intestinal microfold cells (aka M cell; without inflammatory nor diarrhoeal response)
2. Into blood (febrile)

3a. Into gallbladder > bile (as carrier, through enterohepatic circulation)
3b. Into liver/spleen/bone marrow > Kidneys (urine) and Intestines (faeces)

Question 7

What are the clinical features of typhoid fever? (8)

Answer 7

General septic features

1. Fever
2. Malaise
3. Anorexia
4. Confusion

Specific features

1. Pulse-temperature deficit
   - other normal deficit: 1 degrees increase in temperature = increase 10-15 bpm
2. Rose spot: blanchable, maculopapular, erythematous, disappear within few days
3. Splenomegaly
4. Leucopenia (bone marrow suppression)

Question 8

Which of the following are complications of typhoid fever?

A. Intestinal perforation
B. Carrier due to GB colonization
C. 10% relapse rate
D. Paratyphoid fever is more serious compared to typhoid fever
E. Gallstone bacteria will be shedded in faeces

Answer 8

All except D - milder;

A: yes, due to swollen Peyer’s patches (lymphoid follicle in SI)

Question 9

_______ is the gold standard for diagnosing typhoid fever.

Answer 9

Culture

- blood/BM/urine/stool/liver biopsy (rare)

Question 10

What is the usual presentations of typhoid fever patients?

Answer 10

Fever in returning travellers in relatively well young adults

(rule out other travel-related illness e.g. malaria, dengue…)

Question 11

____________test is a serological test that is no longer used. Details:

• Agent: suspension of killed S. typhi as antigens
• Presence of antibody is tested
• Positive result: Tube agglutination

What are the disadvantages of this test? (3)

Answer 11

Widal’s test

1. Delayed diagnosis: detectable after >1-2 weeks
2. Background in titter in endemic regions (patients with background antibodies of S.typhi)
3. Cross-reactivity (false positive in other Salmonella species)

Question 12

What is the treatment for S.typhi infection?

Answer 12

1. Fluoroquinolone (CI in children)

2. 3rd generation cephalosporins

Question 13

What is MDR in S.typhi?

- more severe disease, higher carrier rates

Answer 13

Resistant to ACC

1. Amoxicillin
2. Chloramphenicol
3. Co-trimoxazole (sulphonamides)

Question 14

Prevention of S.typhi? (5)

Answer 14

1. Sanitation: clean water supply and food hygiene (1)
2. Patient control: notification, isolation, contact tracing (3)
3. Epidemic measures: index case search, strain typing (2)

Question 15

What are the 2 types of vaccination available for S.typhi infection?

Answer 15

1. Live oral vaccines (Ty21a): avoid Abx 3days before/after vaccination (will kill the live bacteria)
   - indicated when CD4 >200 in HIV
2. Parenteral Vi polysaccharide vaccine (subunit): SC or IM

Question 16

Why is vaccination not given to everyone?

Answer 16

• Poor efficacy (50-70% protection), require regular booster dose
• Offer to travellers going to endemic regions (2 weeks before travel)