GIS07 Gastrointestinal microbiology and infection

Question 1

Name another causative agent of enteric fever except Salmonella.

Answer 1

Yersinia

Question 2

Describe the pathogenesis of Salmonella typhi / paratyphi.

Answer 2

Intracellular survival in macrophages
Vi antigen: antiphagocytic

Question 3

What antibiotic treatment of typhoid and paratyphoid fevers should you prescribe?

Answer 3

Third generation cephalosporins (e.g. ceftriaxone, cefotaxime)
Fluoroquinolones (e.g. ciprofloxacin, levofloxacin)
Azithromycin (macrolide)

Emerging drug resistance

Question 4

[Practical]
Name the faint, pink macules on the trunk beneath the nipple in a patient with suspected typhoid fever.

Answer 4

Rose’s spots

Question 5

What antigens are added after serial dilution of serum in Widal’s test?

Answer 5

TO (S. Typhi - O Ag)
TH (S. Typhi - H Ag)
AH (S. Paratyphi A - H Ag)
BH (S. Paratyphi B - H Ag)
CH (S. Paratyphi C - H Ag)

Question 6

Epidemic control of Salmonella typhi and paratyphi?

Answer 6

Attention to food (food handler) and water supply

Question 7

Name the class of vaccine against Salmonella typhi in HK.

Answer 7

Vi polysaccharide vaccine

X in HK:
Heat-killed phenol-treated vaccine (limited efficacy)
Ty21a (live-attenuated oral)

Question 8

Name complications of C. difficile-associated diarrhoea starting from the least severe.

Answer 8

Colitis
Pseudomembranous colitis
Toxic megacolon
Perforation