Typhoid Dot Test is Superior to Widal Test for Typhoid Fever Diagnosis
The Typhi dot test (dot enzyme immunoassay) should be used instead of the Widal test for suspected typhoid fever, though blood culture remains the gold standard and serologic tests including Widal should not be relied upon for diagnosis. 1, 2
Why Serologic Tests Should Not Be Used
- The Infectious Diseases Society of America explicitly states that serologic tests should NOT be used to diagnose enteric fever due to poor performance characteristics 1, 2
- The CDC requires isolation of Salmonella typhi from clinical specimens for confirmation and states that serologic evidence alone is not sufficient 2
- Blood culture is the gold standard diagnostic test and should be performed in all patients with clinical suspicion of enteric fever 2, 3
When Serologic Testing Is Considered: Typhi Dot vs Widal
Despite guideline recommendations against serologic testing, if you must choose between these two tests in resource-limited settings where blood culture is unavailable:
Typhi Dot Test Performance
- Sensitivity: 88-95% 4, 5, 6
- Specificity: 90-100% (particularly for IgM) 5, 6
- Positive predictive value: 77-89% 5, 6
- Negative predictive value: 92-97% 5, 6
- Results available within 1 hour 5
Widal Test Performance
- Sensitivity: 43-98% (highly variable) 7, 5
- Specificity: 67-85% 7, 5
- Positive predictive value: 71% 5
- Negative predictive value: 63% 5
Key Advantages of Typhi Dot Over Widal
- Earlier detection: The dot EIA detects IgM antibodies against the 50-kDa outer membrane protein of S. typhi, allowing diagnosis in the first week of illness 7, 6
- Superior specificity: Particularly when detecting IgM alone (100% specificity), avoiding false positives from endemic area exposure 6
- Rapid results: Visual reading within 1 hour versus several hours for Widal 5
- Practical for resource-limited settings: Simple, economical, and doesn't require sophisticated equipment 7, 4
Critical Pitfalls to Avoid
- Do not delay blood culture collection: Obtain 2-3 blood cultures of 20 mL each in adults before starting antibiotics, as this remains the diagnostic gold standard with 40-80% sensitivity 3
- Beware of IgG persistence: IgG antibodies can persist after acute infection, causing false positives; IgM positivity is more specific for acute infection 6
- Consider bone marrow culture: If antibiotics have already been administered or blood cultures remain negative despite high clinical suspicion, bone marrow culture has higher sensitivity than blood 2, 3
Optimal Diagnostic Algorithm
- First-line: Blood culture (2-3 specimens of 20 mL each) before antibiotics 3
- If blood culture unavailable or negative with high suspicion: Bone marrow culture 2, 3
- Adjunctive tests: Stool, duodenal fluid, and urine cultures may be beneficial 1, 2
- Only in resource-limited settings without culture capability: Typhi dot test (NOT Widal test) 5, 6