key: cord-0754774-8mgnq30o authors: Batchi-Bouyou, Armel Landry; Lobaloba, Line; Ndounga, Matthieu; Vouvoungui, Jeannhey Christevy; Mfoutou, Chastel Mapanguy; Boumpoutou, Kamal Rauchelvy; Ntoumi, Francine title: High SARS-COV2 IgG/IGM seroprevalence in asymptomatic Congolese in Brazzaville, the Republic of Congo date: 2020-12-25 journal: Int J Infect Dis DOI: 10.1016/j.ijid.2020.12.065 sha: 8d7c4980a9807ea283439f200be5028df8e7bb0f doc_id: 754774 cord_uid: 8mgnq30o • 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 < 0.0001) and IgM (P < 0.001). 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. The occurrence of asymptomatic individuals with coronaviruses may pose a significant public health issue [1] . As of December 15, 2020, COVI-19 infections occurred globally in more than 73,557,491 cases including 1,637,053 deaths [2] . The United States of America is the most affected country in the world with 16,724,753 patients and 303,849 deaths. In Africa, Africa has the highest number of patients (873,678) and deaths (23, 661) . Congo, with an estimated population of 5,300,000, recorded 6200 cases and 100 deaths until 12 December (SITREP 115, Congo). While most countries, including those in Central Africa, have established procedures for screening symptomatic and case contacts based on virus detection, none have systems in place to systematically detect mild and asymptomatic cases. Obviously, more testing will allow the identification of more asymptomatic individuals, but for low resources countries like many in sub-Saharan Africa, more testing is a daily challenge (https://ourworldindata.org/coronavirus-testing). That is the situation in the Republic of Congo where the capacity of testing has increased since the beginning of the outbreak 14th March 2020 when the first case was detected in the country. With regard to the limitation of testing capacities [3] , it appears difficult to evaluate the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus within the population and referring only on symptomatic cases will not reflect the true situation. In the Republic of Congo, Brazzaville and Pointe-Noire are the major cities and also the cities with the highest number of COVID-19 cases (4087 and 1600 respectively, SITREP 115). Molecular diagnosis of SARS-CoV-2 has been recommended by world health organization (WHO) by using reverse transcription polymerase chain reaction (RT-PCR) [4] . However, the technique is expensive and requires specific molecular equipment, trained human resources and electricity available at any time. The rapid diagnostic tests (RDT) have been developed to detect the antibodies produced against the virus and could be considered as an alternative for the identification of individuals that have been exposed to the infection a minimum of 7 to 14 days before. Therefore, J o u r n a l P r e -p r o o f RDT is relevant for the detection of the presence of IgG and IgM antibodies reflecting the course of the infection and particularly seroconversion when PCR sensitivity has decreased [5] [6] . This tool may inform public health stakeholders on the development of herd immunity within the population The objective of this study was to determine the seroprevalence of SARS-CoV-2 in the Congolese population residing in Brazzaville. The study was conducted in Brazzaville, capital of the republic of the Congo. Individuals were We performed a cross-sectional study by proceeding to an open-invitation screening in Brazzaville using mouth to mouth spread of information and also by contacting most of the biggest companies and societies established in the capital and encouraging their workers to be tested. Only individuals without any disease symptom, aged more than 18 years old and giving a written consent were enrolled. During the interview before enrolment, some of the participants reported to have been in contact with a diagnosed COVID-19 positive patient. The participants were resident of all the districts of Brazzaville. Personal data (age, sex, occupation, place of residence) and oropharyngeal swab and blood samples were collected and stored at -80°C until analysis performance. RNA was extracted using QIAamp Viral RNA Mini kit (Qiagen, Valencia, CA) according to instructions. Qualitative RT-PCR assays to detect SARS-CoV-2 were performed using a clinically validated kit The study was submitted to and approved by the institutional ethics committee of the Fondation The patients tested RT-PCR positive were referred to the health care program for the COVID-19 National response Committee. The overall seroprevalence (IgM+ and/ or IgG+) across the cohort was 19.7% (n=149/754) regardless of the PCR results. In detail, 9.28% (n=70/754) were positive for both IgM and IgG (IgM+IgG+). Regarding the type of detected antibody, IgG+ and IgM+ represented 10.7% (n=81/754) and 13.7% (n=103/753), respectively (Table 1) . In April 2020, the overall reported seroprevalence was 1.7% for IgG and 2.5% for IgM in April and over the months increased to reach 15.5% and 19.8% in July for IgG and IgM, respectively (Figure 1 ). Among these 754 participants, a total of 698 individuals were RT-PCR negative (92.5%). Out of 698 RT-PCR negative, 117 individuals had detectable anti-SARS-CoV-2 antibodies, including 9.2% (n=64/698) with IgG+, 11.5% (n=80/698) with IgM+ and 7.7% (n=54/698) with IgG+ and IgM+ ( Table 1 ). The seroprevalence raised from 1.7 % of IgG+ and 2.5% for IgM+ in April to reach 14.2% of IgG and 17.6% of IgM in July (Figure 1 ). In April, 3.3% and 4.9% of women had detectable IgG and IgM, respectively. While, no detectable IgG and IgM were found in men at the same period of time. In April, May and June, seroprevalence was higher in women but the difference was not statistically different (P=0.081) (Figure 2 ). This study is the first to report the seroprevalence of SARS-CoV-2 in the Congolese population and to our knowledge for Central African population. It is a pilot investigation using two serologic rapid diagnostic tests because the study was conducted during the lockdown in the country with limited additional resources like reagents. This cross-sectional study was carried out as part of a massive screening campaign for the detection of SARS-CoV-2 within the general Congolese population residing in Brazzaville, the capital which is the city with the highest incidence (about 65%) of COVID-19 (SITREP 115, Congo). This study showed that a minimum of 15% of participants were seroconverting, in April (2%) and in July 22%. That is interesting because the lockdown was established from 31 March to 16 May 2020. Analyses of lockdown impact haven shown in some countries that it might have reduced the incidence of the disease [11, 12] . Here, the sample size and the limited number of indicators (situation before lockdown like the number of confirmed and even suspected cases were not available) did not allow to conclude for an impact or not on the number of asymptomatic individuals detected during and after the lockdown. Our results present a high prevalence of SARS-CoV-2 antibodies, much higher than those reported by Seroprevalence studies are good indicators in understanding the scale and spread of the pandemic and predict the probability and timing of future waves of recrudescence [15] . Also, it can address public health questions, such as city lockdown, churches and school closings, travel restrictions and social distancing [15] and future interventions like vaccine and therapeutic initiatives [22] . Furthermore, performing diagnostic tests on individuals based on clinical suspicion can induce selection biases in some cases. Indeed, some authors have shown the importance of considering asymptomatic patients in order to assess with more certainty the prevalence of a disease [16] [17] . In this study, two RDTs were used in order to minimize the risk of false positives and false negatives [18] . Those biases are common when a serological testing is considered at individual level [18] [19] . However, when used at population level, it can help estimate reliable average seroprevalence even with moderate sensitivity and specificity [15] . Only samples positive for both RDTs were considered as positive for IgG or IgM. This would mean that the seroprevalence detected here is really minimized and by using ELISA assays, in the near future, the present findings might be revised. Since the start of the pandemic, the infection has been under-diagnosed because of testing capacities that were not enough for the demand and probably some patients have not been treated and have resolved their infection. This study reported here, is important because it gives a number to missing cases (about 15 to 19%). This seroprevalence is high compared to study carried in Korea (7.6%) where testing capacities were much impressive and virus transmission also [20] . These findings confirm what is reported by the National screening in Congo (75% infection is carried by men) and are almost identical to those reported by Shields et al. [21] . All African countries are developing their vaccine strategies in order to be able to protect their population [23, 24] . In this context, it is important to have an idea of the local herd immunity with the goal to estimate the number of those needing to be vaccinated. The sero-epidemiological data are crucial in that exercise. This work showed that a significant population of Brazzaville represents missing undiagnosed cases. The proportion of the population who seroconvert over the course of the first wave in the Republic of Congo will contribute to better evaluate the risk of future waves and will facilitate the efficient use of limited resources. 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