When to Order the Widal Test in Suspected Enteric Fever in Children
The Widal test should not be routinely ordered for diagnosing enteric fever in children due to its poor diagnostic performance; instead, blood cultures should be obtained before initiating antibiotics in any child with suspected enteric fever, particularly those with fever and systemic signs, those under 3 months of age, or those with recent travel to endemic areas. 1, 2
Primary Diagnostic Approach
Blood cultures are the gold standard and should be collected immediately when enteric fever is suspected, before any antibiotic administration. 1, 2 Blood cultures demonstrate 40-80% sensitivity within the first week of symptom onset. 2
When to Suspect Enteric Fever and Order Blood Cultures
Blood cultures should be obtained in the following clinical scenarios: 1
- Infants <3 months of age with fever and suspected bacterial etiology
- Any child with signs of septicemia or systemic manifestations of infection
- Children with sustained fever despite appropriate management
- Recent travel history to or contact with travelers from enteric fever-endemic areas (South Asia, Southeast Asia, sub-Saharan Africa) presenting with febrile illness of unknown etiology
- Immunocompromised children with fever and diarrhea or systemic symptoms
- Children with high-risk conditions such as hemolytic anemia
Why the Widal Test Should Be Avoided
The Widal test has unacceptably poor diagnostic performance characteristics that make it unreliable for clinical decision-making. 2 Specifically:
- Specificity is only 68.44%, meaning nearly one-third of positive results are false positives 2
- Positive predictive value is extremely poor at 5.7%, meaning that even when the test is positive, there is less than a 6% chance the child actually has typhoid fever 2
- The test lacks sensitivity and specificity, especially in endemic areas where background antibody levels from previous exposure or vaccination are elevated 3
Limited Circumstances Where Widal May Be Considered
If blood culture facilities are absolutely unavailable in resource-limited settings, the Widal test may serve as a screening tool with the following caveats: 4, 5
- Use lower cutoff titers in children: An O- and/or H-titer of ≥1:40 provides sensitivity of 89% and specificity of 89% 4
- A single anti-TH titer ≥1:80 has been shown to have 75% sensitivity and 98% specificity in some pediatric populations 5
- High negative predictive value (99.2%) means a negative Widal can help rule out typhoid, but a positive result cannot confirm it 4
- Even at very high titers (>1:640), the positive predictive value remains below 50% 4
Alternative Diagnostic Approaches When Blood Culture Is Unavailable
When blood cultures cannot be obtained, consider: 1, 3
- Bone marrow cultures have higher sensitivity than blood cultures, particularly valuable if antibiotics have already been administered 1, 3
- Stool, duodenal fluid, and urine cultures may be beneficial but have lower yield 1
- Newer rapid immunochromatographic tests detecting IgM against specific antigens show mixed results but may be superior to Widal in some settings 3, 6
Common Pitfalls to Avoid
- Never rely solely on the Widal test to make treatment decisions given its poor positive predictive value 2
- Never delay blood culture collection while waiting for Widal results 2
- Do not use serologic tests (including Widal) as the primary diagnostic method when culture facilities are available 1
- Recognize that vaccination provides incomplete protection and can cause false-positive Widal results 3
Clinical Action Based on Suspicion Level
If enteric fever is strongly suspected clinically (sustained fever, relative bradycardia, hepatosplenomegaly, travel history), start empiric treatment immediately after collecting blood cultures rather than waiting for Widal results. 1, 2 Azithromycin 20 mg/kg/day (maximum 1g/day) for 7 days is the preferred first-line treatment for children given widespread fluoroquinolone resistance exceeding 70% in endemic regions. 2