High SARS-COV2 IgG/IGM seroprevalence in asymptomatic Congolese in Brazzaville, the Republic of Congo.

• COVID-19 infection from April to July 2020 in Brazzaville. • Seroprevalence using two rapid diagnostic tests. • IgG and IgM seroprevalence higher in Congolese women. • 7.4% of RT-PCR positive asymptomatic Congolese adults. • 15% of seroconverted Congolese adults. Abstract Introduction The republic of the Congo faced its first COVID-19 case on 14 March 2020, and some weeks later initiated individual and country protective measures that are still applied in July, 2020. Along the course of time, the progression of clinical cases appears to be lower than expected based on RT-PCR testing which was quite limited. In order to evaluate the incidence of SARS-CoV-2 within the population, a seroprevalence study was conducted on healthy individuals from different districts of Brazzaville willing to know their infectious status with regard to COVID-19. Methods We collected oropharyngeal swab and blood samples from 754 healthy volunteers for screening between April and July, 2020. Samples were analyzed for SARS-CoV-2 using a qualitative reverse transcription polymerase chain reaction (RT-PCR) assay and Immunoglo bulin G and M were detected using using two different rapid diagnostic tests. Results Out of 754 samples, 56 were found to have active SARS-COV2 infection (7.4%). This means 92.5% (n = 698/754) were RT-PCR negative out of which 117 had detectable anti-SARS-CoV-2 antibodies in their serum. Among these RT-PCR negative subjects, the seroprevalence raised from 1.7% for IgG + and 2.5% for IgM + in April to 14.2% of IgG and 17.6% of IgM in July. No difference was found according to the district of residence (P = 0.108). With regard to gender, 5% of women against 0% of men had either IgG and IgM in April. During the first three months, seroprevalence was significantly higher in women within IgG (P Conclusion The proportion of the population who seroconvert over the course of the first wave is an important data to predict the risk of future COVID-19 waves and this will facilitate the efficient use of limited resources in a low income country like the Republic of the Congo.