Widal Test Interpretation for Typhoid Fever Diagnosis
The serological Widal test lacks sensitivity and specificity and is not recommended for the diagnosis of typhoid fever. 1 Instead, blood cultures remain the gold standard diagnostic method, with the highest yield within the first week of symptom onset.
Diagnostic Value of Widal Test
Despite its limitations, in settings where blood culture facilities are unavailable, the following interpretations of Widal titers can be considered:
- In endemic areas, a single Widal test with O or H agglutinin titers ≥1:80 may be considered positive with appropriate clinical context 2
- Some studies suggest a cutoff titer of ≥1:160 for O antigen as having high specificity and positive predictive value 3
- At a cut-off titer of O agglutinin ≥1:80, diagnostic sensitivity is 90% and specificity 87.3% 2
- For H agglutinin ≥1:80, sensitivity is 90% and specificity 88.5% 2
Limitations of Widal Test
The Widal test has several significant limitations:
- Poor sensitivity and specificity in endemic areas 1
- High background titers in endemic populations (13.8% for O antigen and 8.0% for H antigen at titers ≥1:80) 4
- False positives in patients with immunological disturbances (11.5%) 5
- Variable results based on age, sex, and geographic region 6
- Decreasing positivity rates over time (from 46.4% in 1991 to 25% in 1995) 4
Preferred Diagnostic Methods
Blood cultures should be prioritized over Widal testing:
- Blood cultures have the highest yield within the first week of symptom onset 1
- Sensitivity for blood cultures is reported as 40-80% 1
- Bone marrow cultures have higher sensitivity than blood cultures 1
- Stool and urine cultures become positive after the first week (sensitivity 35-65% and 0-58% respectively) 1
Newer Diagnostic Alternatives
Newer rapid serological tests detecting IgM against specific antigens (e.g., Typhidot, Typhidot-M, Tubex) have been developed but show mixed results 1. PCR techniques may be more reliable but are not widely available in endemic settings.
Clinical Implications
When blood culture facilities are unavailable:
- A single Widal test with O or H agglutinin titers ≥1:80 may be considered presumptive evidence of typhoid fever when combined with appropriate clinical presentation 2
- Higher titers (≥1:160 or ≥1:200) provide stronger evidence 3, 6
- The concept of a single "diagnostic titer" is unreliable; clinical correlation is essential 6
- False negatives are common in early disease (first week), and false positives occur in endemic areas and in patients with immunological disorders 4, 5
In conclusion, while the Widal test has significant limitations, in resource-limited settings where blood cultures are unavailable, titers of ≥1:80 for both O and H antigens may provide presumptive evidence of typhoid fever when interpreted alongside clinical findings.