Field evaluation of a rapid antigen test for mpox in the Democratic Republic of the Congo and Uganda: a multicentre, prospective, diagnostic accuracy study

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BACKGROUND: Accurate, accessible diagnostic tests are essential for mpox outbreak control, particularly in settings with limited laboratory infrastructure. Antigen-based rapid diagnostic tests (RDTs) offer point-of-care potential, but clinical performance data remain scarce. We assessed a research-use-only RDT for detection of mpox at the point of care in two African countries. METHODS: This prospective, multicentre, diagnostic accuracy study of the research-use-only NG-Test Monkeypox antigen RDT (NG Biotech, Guipry-Messac, France) was done at 16 sites (hospitals or health-care facilities) in Uganda and DR Congo. We enrolled individuals of any age with clinically suspected mpox. Paired skin lesion swabs were collected from each participant for antigen testing at the point of care and real-time PCR testing at reference laboratories. Diagnostic accuracy of the antigen test was evaluated using PCR as the reference standard. Diagnostic performance metrics were estimated overall and stratified by country, age, and cycle threshold values. FINDINGS: Between Jan 29 and April 23, 2025, 645 participants were enrolled, of whom 641 (99%) had valid paired antigen and PCR test results and were included in the analysis. 416 (65%) of 641 participants were PCR positive. Overall RDT sensitivity was 70·4% (293 of 416 [95% CI 65·9-74·6]) and specificity was 89·3% (201 of 225 [84·6-92·7]). Sensitivity was higher in Uganda (195 of 238; 81·9% [95% CI 76·6-86·3]) than in DR Congo (98 of 178; 55·1% [47·7-62·2]) Specificity was 86·5% (90 of 104 [95% CI 78·7-91·8]) in Uganda compared with 91·7% (111 of 121 [85·5-95·5]) in DR Congo. Performance varied by age, viral load, and symptom duration. INTERPRETATION: Although performance of the NG-Test Monkeypox antigen RDT did not fully meet WHO Target Product Profile benchmarks, driven mainly by lower sensitivity in DR Congo, results in Uganda were more encouraging. Testing was successfully done under field conditions, including in areas affected by conflict and displacement. These findings should not be interpreted as supporting immediate field deployment but show the feasibility and current limitations of lesion-based antigen testing and the need for improved, validated assays. FUNDING: Global Virus Network, UK Medical Research Council, and University of St Andrews. TRANSLATIONS: For the Swahili and French translations of the abstract see Supplementary Materials section.

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