The magnitude of the 2022 multi-country monkeypox virus (MPXV) outbreak has surpassed any preceding outbreak. It is unclear whether asymptomatic or otherwise undiagnosed infections are fuelling this epidemic. In this study, we aimed to assess whether undiagnosed infections occurred among men attending a Belgian sexual health clinic in May 2022. We retrospectively screened 224 samples collected for gonorrhea and chlamydia testing using an MPXV PCR assay and identified MPXV-DNA-positive samples from four men. At the time of sampling, one man had a painful rash, and three men had reported no symptoms. Upon clinical examination 21–37 days later, these three men were free of clinical signs, and they reported not having experienced any symptoms. Serology confirmed MPXV exposure in all three men, and MPXV was cultured from two cases. These findings show that certain cases of monkeypox remain undiagnosed and suggest that testing and quarantining of individuals reporting symptoms may not suffice to contain the outbreak.

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COVID-19 Antibody Detecting Rapid Diagnostic Tests (COVID-19 Ab RDTs) are the preferred tool for SARS-CoV-2 seroprevalence studies, particularly in low- and middle-income countries. The present study challenged COVID-19 Ab RDTs with pre-pandemic samples of patients exposed to tropical pathogens. A retrospective study was performed on archived serum (n = 94) and EDTA whole blood (n = 126) samples obtained during 2010–2018 from 196 travelers with malaria (n = 170), schistosomiasis (n = 25) and dengue (n = 25). COVID-19 Ab RDTs were selected based on regulatory approval status, independent evaluation results and detecting antigens. Among 13 COVID-19 Ab RDT products, overall cross-reactivity was 18.5%; cross-reactivity for malaria, schistosomiasis and dengue was 20.3%, 18.1% and 7.5%, respectively. Cross-reactivity for current and recent malaria, malaria antibodies, Plasmodium species and parasite densities was similar. Cross-reactivity among the different RDT products ranged from 2.7% to 48.9% (median value 14.5%). IgM represented 67.9% of cross-reactive test lines. Cross-reactivity was not associated with detecting antigens, patient categories or disease (sub)groups, except for schistosomiasis (two products with ≥60% cross-reactivity). The high cross-reactivity for malaria, schistosomiasis and—to a lesser extent—dengue calls for risk mitigation when using COVID-19 Ab RDTs in co-endemic regions.

Abstract Background Hepatitis C virus (HCV) screening is critical to HCV elimination efforts. Simplified diagnostics are required for low-resource settings and difficult-to-reach populations. This retrospective study assessed performance of rapid diagnostic tests (RDTs) for detection of HCV antibodies. Methods Two lots of 13 RDTs were evaluated at three laboratories using archived plasma samples from four countries (Nigeria, Georgia, Cambodia, Belgium). HCV status was determined using three reference tests according to a composite algorithm. Sensitivity and specificity were evaluated in HIV infected and HIV uninfected populations. Operational characteristics were also assessed. Results In total, 1,710 samples met inclusion criteria. In HIV uninfected samples (n=384), the majority of RDTs had sensitivity ≥98% in one or both lots and most RDTs had specificity ≥99%. In HIV infected samples (n=264), specificity remained high, but sensitivity was markedly lower than in HIV uninfected samples; only one RDT reached >95%. The majority of HIV infected samples for which sensitivity was low did not have detectable HCV viral load/core antigen. Inter-reader variability, lot-to-lot variability and rate of invalid runs were low for all RDTs (<2%). Conclusion HCV RDTs should be evaluated in the intended target population, as sensitivity can be impacted by population factors such as HIV status.

BackgroundMonkeypox is transmitted by close contact with symptomatic cases, and those infected are assumed to be uniformly symptomatic. Evidence of subclinical monkeypox infection is limited to a few immunological studies which found evidence of immunity against orthopoxviruses in asymptomatic individuals who were exposed to monkeypox cases. We aimed to assess whether asymptomatic infections occurred among individuals who underwent sexually transmitted infection (STI) screening in a large Belgian STI clinic around the start of the 2022 monkeypox epidemic in Belgium.MethodsAnorectal and oropharyngeal swabs collected for gonorrhoea/chlamydia screening from May 1 until May 31, 2022 were retrospectively tested by a monkeypox-specific PCR. Cases with a positive PCR result were recalled to the clinic for case investigation, repeat testing and contact tracing.FindingsIn stored samples from 224 men, we identified three cases with a positive anorectal monkeypox PCR. All three men denied having had any symptoms in the weeks before and after the sample was taken. None of them reported exposure to a diagnosed monkeypox case, nor did any of their contacts develop clinical monkeypox. Follow-up samples were taken 21 to 37 days after the initial sample, by which time the monkeypox-specific PCR was negative, likely as a consequence of spontaneous clearance of the infection.InterpretationThe existence of asymptomatic monkeypox infection indicates that the virus might be transmitted to close contacts in the absence of symptoms. Our findings suggest that identification and isolation of symptomatic individuals may not suffice to contain the outbreak.FundingInstitutional fundingResearch in contextEvidence before this studySimilar to smallpox, monkeypox is transmitted through close contact with symptomatic cases, and 100% of those infected are assumed to develop symptoms. These features imply that an outbreak in the general population tends towards extinction with relatively minor hygienic measures, as observed in several outbreaks in endemic regions. If, however, asymptomatic transmission occurs, the outbreak becomes much more difficult to contain.We searched PubMed and Google Scholar for evidence of asymptomatic human monkeypox, using the search terms “monkeypox” AND (“asymptomatic” OR “subclinical”), and included peer-reviewed reports published until June 17, 2022. We identified seven original reports in three different epidemiological settings which reported indirect, immunological evidence of asymptomatic monkeypox infection in a small number of people who were exposed to the virus. We did not find any study that provided direct evidence of the virus in asymptomatic individuals.Added value of this studyBy retrospectively screening clinical samples collected for sexually transmitted infection screening in our centre throughout May 2022 with a monkeypox-specific PCR, we found evidence of asymptomatic monkeypox virus infection in three individuals.Implications of all the available evidenceThe existence of asymptomatic monkeypox infection indicates that the virus may be transmitted in the absence of symptoms. This risk can be further quantified by studying viral dynamics in contacts of symptomatic and asymptomatic monkeypox cases. Our findings suggest that identification and isolation of symptomatic individuals may not suffice to contain the outbreak.