Sensitivity and Specificity of Cholera Antigen Stool Tests
The sensitivity of cholera antigen stool tests ranges from 72-90% and specificity ranges from 87-95% when tested directly on stool samples, with improved specificity of 97-100% after enrichment. 1, 2
Performance of Different Cholera Rapid Diagnostic Tests
Direct Testing (Without Enrichment)
- SD Bioline Cholera test shows sensitivity of 90.9% and specificity of 95.2% when compared to a reference standard combining culture and PCR 2
- Crystal VC demonstrates high sensitivity (72-98.6%) but moderate specificity (71.1-86.8%) in direct testing 1, 3
- Cholkit (locally produced RDT in Bangladesh) shows sensitivity of 76% and specificity of 90.2%, comparable to commercial tests 1
- SMART-II Cholera O1 test shows the highest sensitivity (86.1%) among RDTs in direct testing 4
After Enrichment
- SD Bioline's performance improves significantly after enrichment, with sensitivity of 95.5% and specificity of 100% 2
- Crystal VC shows sensitivity of 68% and improved specificity of 97.5% after enrichment 1
- SMART-II maintains high sensitivity (78.8%) after enrichment 4
Factors Affecting Test Performance
- Sample preparation: Enrichment in alkaline peptone water generally improves specificity but may slightly reduce sensitivity in some tests 4, 1
- Reference standard: Performance metrics vary depending on whether culture alone or culture plus PCR is used as the reference standard 2
- Test interpretation: Some tests (Crystal VC and Artron) frequently show false positive O139 bands 3
- Disease severity: Performance may vary based on bacterial load in stool samples 4
Limitations and Considerations
- PCR-based detection methods show superior sensitivity (98.4%) compared to antibody-based RDTs but lower specificity (75.3%) 4
- Newer molecular diagnostic approaches like Rapid LAMP-based Diagnostic Tests (RLDT) can detect approximately 10⁴ CFU/gm of stool within 40 minutes 5
- Most evaluations have been conducted in endemic settings where V. cholerae O1 is the predominant serotype 1
- RDTs are most useful in outbreak/epidemic situations where rapid detection is critical for public health response 4
Practical Applications
- Cholera RDTs meet the Global Task Force for Cholera Control recommendations (sensitivity ≥90%, specificity ≥85%) when properly used 2
- These tests are valuable in resource-limited settings without laboratory infrastructure for culture-based diagnosis 3
- For optimal results, tests should be performed on fresh liquid stool samples that conform to the shape of the container 4
- While not ideal for individual clinical diagnosis due to suboptimal specificity in direct testing, these tests are valuable for outbreak detection and surveillance 3