What is the investigation of choice for enteric fever in children?

Investigation of Choice in Enteric Fever for Children

Blood culture is the primary diagnostic method for enteric fever in children, with a sensitivity of 40-80%, and should be performed before initiating antibiotic therapy. 1

Diagnostic Approach Algorithm

First-line Investigations

1. Blood Culture

   • Gold standard for diagnosis
   • Collect before antibiotic administration
   • Two sets recommended for optimal sensitivity
   • Sensitivity: 40-80%
   • May take several days for results 1, 2

2. Complete Blood Count

   • May show leukopenia or normal white cell count
   • Anemia may be present in prolonged cases 1

3. Liver Function Tests and Renal Function Tests

   • To assess organ involvement and guide management 1

Rapid Diagnostic Tests (when immediate results needed)

1. Molecular Testing (PCR-based methods)

   • Higher sensitivity (84.5%) compared to blood culture (61.8%)
   • Faster results (within hours)
   • Particularly useful for detecting both S. Typhi and S. Paratyphi A 1, 3

2. Serological Tests

   • Typhidot Test (preferred over Widal)

     • Dot enzyme immunoassay
     • Sensitivity: 85-97%
     • Specificity: 77-97%
     • Rapid results (within hours) 1, 4

   • Widal Test (less reliable)

     • Poor sensitivity (34-72%) and specificity (42-87%)
     • Requires paired sera for optimal interpretation
     • Limited utility in endemic areas 1

Enhanced Diagnostic Methods

• Blood Culture PCR Method
  • Combines short culture with PCR
  • Can detect bacteria at low concentrations (0.75 CFU/mL)
  • Results available in under 8 hours
  • Higher sensitivity than conventional blood culture 2, 3

Special Considerations

When to Suspect Enteric Fever

• Sustained fever
• Headache
• Lethargy and malaise
• Relative bradycardia
• Abdominal pain
• Hepatosplenomegaly 1

Important Pitfalls to Avoid

1. Relying solely on serological tests - Widal test has poor sensitivity and specificity, especially in endemic areas 1

2. Starting antibiotics before collecting blood cultures - Reduces culture sensitivity significantly 1

3. Failure to consider mixed infections - S. Typhi and S. Paratyphi A can co-exist, requiring laboratory strategies to detect both 5

4. Inadequate blood volume - Insufficient blood volume reduces culture sensitivity, especially in children 3

High-Risk Scenarios Requiring Prompt Investigation

• Recent travel to endemic areas
• Exposure to confirmed cases
• Persistent fever without clear source
• Children with fever and abdominal symptoms 1, 6

Follow-up Testing

• Follow-up testing is not recommended for most patients following resolution of symptoms
• Serial stool specimens using culture-dependent methods may be required in certain situations by local health authorities to enable return to school or childcare 7

Blood culture remains the cornerstone of diagnosis despite its limitations, but newer molecular methods offer improved sensitivity and faster results, which can facilitate earlier appropriate treatment and potentially improve outcomes in children with enteric fever.