Diagnostic accuracy of three mpox lateral flow assays for antigen detection in the Democratic Republic of Congo and the United Kingdom

Summary Background The ongoing outbreaks of mpox, the disease caused by monkeypox virus (MPXV) highlight the urgent need for a rapid and low-cost MPXV diagnostic test to accurately detect and control mpox disease. In this study we assessed the diagnostic accuracy of three brands of rapid diagnostic tests for antigen detection (Ag–RDT) of MPXV. Methods We estimated the clinical diagnostic performance of FlowFlex Monkeypox Virus Antigen Rapid Test (ACON Biotech Co., Ltd., Hangzhou, China), Ecotest Monkeypox Antigen Rapid Test (Assure Tech. Co., Ltd, Hangzhou, China), and STANDARD Q Monkeypox Ag Test (SD Biosensor, Inc. Republic of Korea) using skin lesion swabs (SS) and upper–respiratory tract swabs (URS) from 68 participants in the Democratic Republic of the Congo (DRC) and from 16 in the United Kingdom (UK). The limit of detection (LOD) of the three Ag–RDT brands was evaluated using viral culture of the MPXV of the IIb lineage (EVAg, France). Findings Although the specificity of the three Ag–RDT was high (100%), sensitivity was estimated as 15·79% (95% CI, 5·52–37·57%) for Flowflex and Ecotest and as 10·53% (95% CI, 2·94–31·39%) for Standard–Q using SS in the DRC. The sensitivity was estimated as 0.00% (95% CI, 0·0–20·6%) among URS in the DRC. In the UK, the sensitivity of the three Ag-RDT was 0.00% among SS (95% CI, 0·0–12·7%) and among URS (95% CI, 0·0–21·5%). The LOD of all Ag–RDT was determined to be 1·0× 10 4 pfu/ml (1·3×10 5 copies/mL) using viral culture. Interpretation None of the three Ag–RDT reached the target clinical sensitivity and thus we do not recommend these as diagnostic or screening tool for suspected mpox cases. Marked improvement in sensitivity are needed for these Ag–RDT prior adoption. The recommended analytical LOD in the WHO target product profile (TPP) is at 10 6 pfu/mL, being fulfilled by the three brands of Ag–RDTs suggesting that the analytical LOD stated in the TPP does not align with the desired clinical sensitivity. There remains an urgent need for accurate rapid Ag-RDTs for mpox diagnosis.