💡 In one sentence: The Widal test detects antibodies against Salmonella typhi in the blood, providing evidence of typhoid fever infection — but it has significant limitations in Nigeria and must be interpreted in clinical context.
What Does Widal Test Measure?
The Widal test uses a patient's serum to agglutinate (clump) Salmonella typhi antigens in a tube or slide. The dilution at which agglutination still occurs is reported as a titre. It measures the immune response to typhoid — not the bacteria directly. The test detects two types of antibodies: O antibodies (against the bacterial cell body — rise early and fall faster) and H antibodies (against the flagellum — rise later but persist longer). A rising titre over time (two samples 7–10 days apart) is more meaningful than a single reading. In Nigeria, a titre of 1:160 or above is generally considered significant — but this threshold was set for non-endemic populations and is unreliable in areas where typhoid is common.
Understanding Abnormal Results
⬆️ High Widal Test may indicate:
O titre ≥1:160 with fever, abdominal pain, and stepladder temperatureClinically consistent with typhoid — treat with appropriate antibiotics (ceftriaxone, azithromycin, or ciprofloxacin depending on local resistance)
H titre elevated without O titreMore likely previous vaccination or past infection than active typhoid — less clinically meaningful than O titre
Frequently Asked Questions
Is the Widal test reliable for diagnosing typhoid?
The Widal test is widely used in Nigeria but has well-documented limitations. False positives occur in: endemic areas (prior exposure raises baseline titres), previous vaccination, other bacterial infections, malaria co-infection, and liver disease. False negatives occur in: early infection (antibodies not yet risen), antibiotic pre-treatment, and immunosuppressed patients. Blood culture — growing Salmonella typhi from a blood sample — is the gold standard with 80–90% sensitivity in the first week of illness. In Nigeria, the Widal is used pragmatically when culture is unavailable, but its result alone should not drive treatment without clinical correlation.
What titre is significant for typhoid in Nigeria?
The traditional threshold of 1:160 for O antibodies was derived from studies in populations where typhoid exposure is low — this makes the test more specific there. In Nigeria, where typhoid is endemic and many people have had prior exposure (raising background titres), a single 1:160 result is less meaningful. Some Nigerian clinicians use 1:320 as a more reliable threshold in endemic areas, and/or require two rising titres. A rising titre — comparing samples taken 7–10 days apart — is more diagnostically meaningful than any single value.
My child has a Widal of 1:320 — definitely typhoid?
Not definitely — but clinically suggestive, especially with the right symptoms (fever >5 days, abdominal pain, relative bradycardia, headache, fatigue, constipation early then diarrhoea). In a febrile child in Nigeria with 1:320 and no alternative explanation, empirical typhoid treatment is reasonable. However, 1:320 can also be seen in: prior typhoid infection with persistent antibodies, untreated malaria causing false elevation, and non-typhoidal Salmonella. If the child does not respond to typhoid treatment within 48–72 hours, blood culture and broader investigation are warranted.
Why does my Widal keep coming back positive even after treatment?
Widal antibodies — particularly H antibodies — can persist for months to years after typhoid infection or treatment. A positive Widal 3–6 months after successful typhoid treatment does not mean you are still infected. This is one of the most common sources of unnecessary antibiotic prescriptions in Nigeria. In a patient who has had documented typhoid, a repeat Widal titre is not useful for monitoring — clinical response (resolution of fever, return of appetite and energy) is the most relevant indicator of cure.