Background: By the end of the third wave of the coronavirus disease 2019 (COVID-19) epidemic (May–October 2021), only 3130 of the 57 268 confirmed cases of coronavirus disease 2019 (COVID-19) in the Democratic Republic of the Congo (DRC) were reported in Kongo Central. This province, and especially its capital city, Matadi, has essential trade and exchanges with Kinshasa, the epicenter of the COVID-19 epidemic in DRC. Kinshasa accounted for 60.0% of all cases during the same period. The true burden of COVID-19 in Matadi is likely underestimated. In this study, we aimed to determine the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) seroprevalence and associated risk factors after the third wave in Matadi. Methods: We conducted a population-based cross-sectional study in October 2021. Consenting participants were interviewed and tested using an enzyme-linked immunosorbent assay commercial kit. We applied univariable and multivariable analysis to evaluate factors associated with seropositivity and adjusted the seroprevalence for the test kit performance. Results: We included 2210 participants from 489 households. Female participants represented 59.1%. The median age was 27 years (interquartile range, 16–45 years). The crude SARS-CoV-2 seroprevalence was 82.3%. Age was identified as the main risk factor as younger age decreased the seropositivity odds. Accounting for clustering at the household level increased the seroprevalence to 83.2%. The seroprevalence increased further to 88.1% (95% confidence interval, 86.2%–90.1%) after correcting for the laboratory test kit performance. Conclusions: The SARS-CoV-2 seroprevalence was very high, contrasting with reported cases. Evidence generated from this population-based survey remains relevant in guiding the local COVID-19 response, especially vaccination strategies.

We conducted a study to evaluate the sensitivity (Se), specificity (Sp), positive predictive value (PPV), and negative predictive value (NPV) of five serologic tests. Subjects with negative or positive COVID-19 polymerase chain reaction (PRC) test results were tested with each of the serological tests. The results were compared with the reference PCR test. For the five tests evaluated, the Se ranged from 55.0% to 70.0% and the Sp ranged from 67.2% to 86.2%. PPV ranged from 53.2% to 80% and NPV from 75.0% to 86.2%. One test, the Wantai, had better specificity and sensitivity. None of the five tests had performance values of more than 90% in the entire sample. In symptomatic positive cases, the Wantai test reported excellent sensitivity. Overall, the low level of diagnostic performance of these tests does not support their use as an alternative to PCR for COVID-19 diagnostic. Test with better performance can be used for mass screening in low prevalence populations, to limit the indiscriminate use of PCR in context of resource-limited countries. Given the excellent sensitivity of Wantai in symptomatic cases, this test could be used as a referral test only in health facilities to discriminate suspected cases before PCR confirmation.