Typhoid and Paratyphoid Fever

Question 1

Organism

Answer 1

Salmonella enterica subspecies enterica:

• serovar Typhi = S. Typhi
• serovar Paratyphi A, B, C = S. Paratyphi
• gram -ve bacilli, enterobacteriaceae, motile
• antigen O (somatic; cell surface), H (flagella) and Vi (capsule)

Question 2

Typhoid fever: risk factors, transmission, pathogenesis

Answer 2

Salmonella but NOT enteric or diarrhoea disease!!!! Different group!!!

• human as the ONLY HOST (human-to-human spread; contact tracing)
• transmission: faecal-oral (contaminated water and food)
• not acid resistant: infective dose 10000 bacteria; increased risk in achlorhydria
• invade intestinal mucosa (inside Peyer’s patches) without inflammatory or diarrhoea response –> enter blood (systemic)
  ==> liver/ spleen/ BM –> excreted in urine and faeces
  +
  ==> enter gallbladder and adhere to gallstones/ persist (colonise) ==> CARRIER (periodic shedding into bile and faeces)

Question 3

Typhoid fever: clinical features

Answer 3

Incubation: 10-14 days

General septic features: fever, malaise, anorexia, confusion

Specific features:

• PULSE TEMPERATURE DEFICIT - abnormal physiological response (relative bradycardia) to high fever
• ROSE SPOT: <12 erythematous maculopapular lesions on abdomen, blanchable, 2-4 mm, disappear within a few days
• SPLENOMEGALY
• LEUCOPENIA: due to myelosuppression (infect BM) c.f. other infections increase WBC

Question 4

Typhoid fever: outcome and complications

Answer 4

Outcome:

• resolve within 3-4 wks
• 10% mortality

Complications:

• 10% in untreated cases, lasts >2 wks
• intestinal perforation (swollen Peyer’s patches)
• intestinal haemorrhage
• 10% relapse
• 3% carriers (asymptomatic with periodic shedding into faeces)

Question 5

Paratyphoid fever features

Answer 5

Similar pathogenesis and clinical presentation as typhoid fever

Milder clinical course with less perforation, haemorrhage and lower mortality

Question 6

Typhoid fever: diagnosis

Answer 6

Fever in returning travellers
Relatively well young adults (not reflective of high fever i.e. not tired, nauseated, no myalgia etc.)

• need to rule out other travel-related illnesses e.g. malaria, dengue

Lab:
- CULTURE (gold standard): blood, urine, stool, (BM if other 3 not revealing)

• Serology: Widal’s test (no longer used)
• – suspension of killed S. typhoid mixed with patient serum to detect presence of Ab by agglutination (dilute and titre)
• – limitations: cross reactivity (other salmonella species), background titre in endemic regions (residual Ab from past infections), not detectable until 1 wk after illness (delay diagnosis)

Question 7

Typhoid fever: treatment, resistance

Answer 7

Emerging resistance to 3 antibiotics:

• ampicillin, chloramphenicol and co-trimoxazole
• resistant to all 3 - MDR strain
• more severe disease and higher carriage rates

Current drug regime:

• fluoroquinolone (c.f. <12 yrs old) or 3rd generation cephalosporin
• 10-14 days

Question 8

Prevention

Answer 8

Sanitation (water supply, food hygiene and handling)
Patient control: NOTIFICATION, isolation and contact tracing
Epidemic measures: index case search, strain typing

Vaccination
- live oral vaccine (Ty21a): don’t take antibiotics 3 days before/after; CD4>200 in HIV
- parenteral Vi polysaccharide vaccine: subcutaneous or intramuscular
==> poor efficacy (50-70% protection), requires regular boost
==> only indicated in travellers to endemic countries/ outbreak control/ areas of high MDR strain resistance (ineffective treatment)