What investigations are done for typhoid fever on a week-by-week basis?

Diagnostic Investigations for Typhoid Fever: Week-by-Week Approach

Blood culture is the primary diagnostic method for typhoid fever and should be collected prior to antibiotic therapy, with at least two sets of cultures recommended for optimal sensitivity of up to 80%. 1

Initial Diagnostic Workup (Week 1)

• Blood cultures: The gold standard for diagnosis with sensitivity of 40-80%

  • Collect at least two sets before starting antibiotics 1
  • Positive results typically appear within 2-3 days

• Complete blood count:

  • Look for thrombocytopenia (common finding) 1
  • White blood cell count may be normal, elevated, or decreased

• Liver and renal function tests:

  • To assess hepatic involvement and guide treatment 1
  • Elevated liver enzymes are common

• Rapid diagnostic tests:

  • Typhidot test: Higher sensitivity (85-97%) and specificity (77-97%) than Widal test 1
  • Results available within hours

Follow-up Investigations (Week 2)

• Molecular testing:

  • PCR-based methods with sensitivity of 84.5% (compared to blood culture at 61.8%) 1
  • Particularly useful if blood cultures are negative but clinical suspicion remains high

• Widal test:

  • Traditional serological test with poor sensitivity (34-72%) and specificity (42-87%) 1
  • Requires paired sera for optimal interpretation
  • A local cut-off titer of 1:80 may be used for both O-agglutinin and H-agglutinin (sensitivity 47.8%, specificity 99.4%) 2

• Stool and urine cultures:

  • May become positive in the second week of illness
  • Helpful for identifying carriers and monitoring clearance

Later Investigations (Week 3-4)

• Follow-up blood cultures:

  • To confirm clearance of bacteremia
  • Particularly important in complicated cases

• Imaging studies (if complications suspected):

  • Abdominal ultrasound to assess for hepatosplenomegaly or complications
  • Chest X-ray if pulmonary involvement is suspected

• Bone marrow culture (in selected cases):

  • Higher sensitivity than blood culture, especially after antibiotic use
  • Considered when blood cultures are negative but clinical suspicion remains high

Important Clinical Considerations

• Clinical signs and symptoms of typhoid fever are non-specific and may not significantly differ from other febrile illnesses 2
• Longer duration of fever prior to admission may be associated with typhoid fever 2
• The WHO case definition for suspected typhoid fever has a sensitivity of 82.6% and specificity of 41.3% 2

Common Pitfalls to Avoid

• Relying solely on the Widal test for diagnosis 1
• Failing to collect blood cultures before starting antibiotics 1
• Using fluoroquinolones empirically without considering regional resistance patterns 1
• Overlooking typhoid fever in patients with non-specific symptoms, as clinical presentation can be variable

Blood culture remains the cornerstone of diagnosis, but a combination of clinical assessment and laboratory investigations provides the most accurate approach to diagnosing typhoid fever on a week-by-week basis.