- Design
- Retrospective diagnostic accuracy study against PCR
- Population
- Lesion swabs from 190 patients with suspected mpox, Kinshasa province, DR Congo
- Primary outcome
- Sensitivity and specificity of five antigen rapid tests
- Effect
- Best test: sensitivity 77.3% (68.0–84.5), specificity 93.5% (86.6–97.0); lowest sensitivity 39.2%
Where mpox PCR is unavailable, antigen-based rapid tests are an obvious stopgap. A diagnostic accuracy study in The Lancet Infectious Diseases, published on 25 May, tested five of them against PCR on lesion swabs from 190 patients with suspected mpox in Kinshasa province, DR Congo, where clade Ib circulates.
The best-performing test detected 77.3% of PCR-positive cases (95% CI 68.0 to 84.5) with 93.5% specificity; a second was similar at 72.2%. The others ranged down to 39.2% sensitivity, all with specificity of 93–97%. In a high-prevalence setting like this, a positive result is therefore likely to be real; a negative result misses at least a quarter of infections even with the best test.
For clinicians outside the outbreak area, including in India, PCR remains the test to use for suspected mpox. Where a rapid test is all that is available, act on a positive, but keep isolating and seek PCR for a patient with typical lesions and a negative rapid test. Performance will be lower where mpox is rare, because positive predictive value falls with prevalence.
- Use PCR on a lesion swab as the diagnostic test for suspected mpox wherever it is available.
- A positive antigen test in a high-prevalence setting can support diagnosis when PCR is not available.
- A negative antigen test does not rule out mpox; keep isolation and seek PCR if lesions are typical.
- Rapid tests differ widely; sensitivity ranged from 39% to 77% across five products.
Why it matters
A falsely reassuring negative test could send an infectious patient home.
Don't overread it
Performance was measured in a high-prevalence clade Ib setting; accuracy elsewhere and with other clades may differ.
The statistics, in plain English
Sensitivity of 77% means 23 of every 100 true infections test negative. Specificity of 93.5% means about 6 of every 100 people without mpox test positive. How much a positive result can be trusted depends on how common mpox is locally: in an outbreak it is high, where mpox is rare many positives would be false.
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