What are the sensitivity and specificity of the Widal test for diagnosing acute typhoid fever?

Sensitivity and Specificity of the Widal Test

The Widal test should not be used for diagnosing typhoid fever due to its poor performance characteristics, with sensitivity ranging from 52-80% and specificity from 51-88%, along with a very poor positive predictive value of only 5.7-38%. 1, 2, 3

Guideline Recommendations

• The Infectious Diseases Society of America (IDSA) explicitly recommends against using the Widal test for diagnosing enteric (typhoid) fever because of its poor performance characteristics and inability to replace culture-based diagnosis. 1

• Blood culture remains the gold standard for typhoid fever diagnosis and should be obtained before starting antibiotics, with the highest diagnostic yield (40-80% sensitivity) within the first week of symptom onset. 1, 2, 4

• The CDC states 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. 4

Test Performance Characteristics

Sensitivity (ability to detect disease when present):

• O antigen antibodies: 52-80% sensitivity depending on the cutoff titer used 5, 3, 6

  • At ≥1:80 cutoff: 64% sensitivity (acute phase) 5
  • At ≥1:200 cutoff: 52% sensitivity (acute phase), increasing to 90% in convalescent phase 6
  • Overall reported: 71.4% 3

• H antigen antibodies: 72-80% sensitivity, but less reliable than O antigens 7, 3

Specificity (ability to exclude disease when absent):

• O antigen antibodies: 51-88% specificity 7, 3, 6

  • At ≥1:80 cutoff: 100% specificity but only 64% sensitivity 5
  • At ≥1:200 cutoff: 88% specificity (acute phase), 90% in convalescent phase 6
  • Overall reported: 68.44% 3

• H antigen antibodies: 58-82% specificity, consistently lower than O antigens 7, 3

Predictive Values:

• Positive Predictive Value (PPV): Only 5.7-38%, meaning most positive results are false positives 2, 3, 6

• Negative Predictive Value (NPV): 71-98.9%, indicating that negative results are more reliable for excluding disease 3, 6

Critical Limitations and Pitfalls

• False positives occur due to:

  • Previous typhoid vaccination 4
  • Prior typhoid infection 4
  • Cross-reactions with other Salmonella species 4
  • Elevated background antibody levels in endemic areas 4
  • Other febrile illnesses 4

• False negatives occur due to:

  • Prior antibiotic treatment 4
  • Immunosuppression 4
  • Testing too early in the disease course 6

• Significant inter-brand variability: Different commercial Widal test kits show markedly different sensitivities and specificities, making results inconsistent and unreliable. 8

• Single versus paired samples: Four-fold rise in antibody titers (the traditional diagnostic criterion) is often not demonstrable even in confirmed typhoid fever patients, making paired serum testing unreliable. 8

Superior Alternative Tests

• ELISA (IgG/IgM): Sensitivity of 95-96% and specificity of 94-95%, with PPV of 77-78%, significantly outperforming the Widal test 7

• Tubex test: Sensitivity of 60-78% and specificity of 89-99%, superior to Widal but should not replace blood culture 1

• Blood culture: Remains the gold standard with up to 80% sensitivity when performed within the first week of symptoms 2, 4