Diagnosing Typhoid Fever
Understanding the Widal Test
- The Centers for Disease Control and Prevention (CDC) guidelines state that the Widal test alone is not sufficient for diagnosing typhoid fever, as isolation of Salmonella typhi from blood, stool, or other clinical specimens is required for confirmation 1
- The Widal test detects agglutinating antibodies against O and H antigens of Salmonella Typhi and Paratyphi, but it lacks sensitivity and specificity, especially in endemic areas where background antibody levels may be elevated 2
- Blood culture remains the gold standard for diagnosis of typhoid fever, with the highest yield within the first week of symptom onset 2
Limitations of the Widal Test
- The CDC guidelines state that serologic evidence alone is not sufficient for diagnosis 1
- False positives may occur due to cross-reactions with other Salmonella species 1
- False positives may also occur due to previous typhoid vaccination, prior typhoid infection, or other febrile illnesses 2
- False negatives may occur due to prior antibiotic treatment or immunosuppression 2
Diagnostic Algorithm
- Consider clinical presentation consistent with typhoid fever, including sustained fever, headache, malaise, anorexia, relative bradycardia, constipation or diarrhea, and nonproductive cough 1
- Obtain blood cultures, which have the highest yield within the first week of symptoms 2
- Blood cultures may remain negative in 87.5-95% of cases 3