key: cord-346299-2s9j01q7 authors: Salim Khan, S Muhammad; Qurieshi, Mariya Amin; Haq, Inaamul; Majid, Sabhiya; Bhat, Arif Akbar; Nabi, Sahila; Ganai, Nisar Ahmad; Zahoor, Nazia; Nisar, Auqfeen; Chowdri, Iqra Nisar; Qazi, Tanzeela Bashir; Kousar, Rafiya; Lone, Abdul Aziz; Sabah, Iram; Nabi, Shahroz; Sumji, Ishtiyaq Ahmad; Kawoosa, Misbah Ferooz; Ayoub, Shifana title: Seroprevalence of SARS-CoV-2 specific IgG antibodies in District Srinagar, northern India – a cross-sectional study date: 2020-09-04 journal: bioRxiv DOI: 10.1101/2020.09.04.282640 sha: doc_id: 346299 cord_uid: 2s9j01q7 Background Prevalence of IgG antibodies against SARS-CoV-2 infection provides essential information for deciding disease prevention and mitigation measures. We estimate the seroprevalence of SARS-CoV-2 specific IgG antibodies in District Srinagar. Methods 2906 persons >18 years of age selected from hospital visitors across District Srinagar participated in the study. We tested samples for the presence of SARS-CoV-2 specific IgG antibodies using a chemiluminescent microparticle immunoassay-based serologic test. Results Age- and gender-standardized seroprevalence was 3.6% (95% CI 2.9% to 4.3%). Age 30-69 years, a recent history of symptoms of an influenza-like-illness, and a history of being placed under quarantine were significantly related to higher odds of the presence of SARS-CoV-2 specific IgG antibodies. The estimated number of SARS-CoV-2 infections during the two weeks preceding the study, adjusted for test performance, was 32602 with an estimated (median) infection-to-known-case ratio of 46 (95% CI 36 to 57). Conclusions The seroprevalence of SARS-CoV-2 specific IgG antibodies is low in the District. A large proportion of the population is still susceptible to the infection. A sizeable number of infections remain undetected, and a substantial proportion of people with symptoms compatible with COVID-19 are not tested. in a population since they may miss many asymptomatic and pre-symptomatic infections. Thus, 4 60 an informed policy-and decision-making for control of the COVID-19 epidemic in a community 61 should not be based solely on RT-PCR-based numbers. Seroprevalence surveys can provide an estimate of the proportion of the population that has 63 developed antibodies against SARS-CoV-2, an indication of recent SARS-CoV-2 infection. Mild 64 and asymptomatic infections, which may not have received RT-PCR testing, can be detected. 65 Besides, assuming that antibodies provide partial or total immunity, seroprevalence surveys give Here, we present the results of a cross-sectional seroprevalence study in District Srinagar, 70 conducted between 1 st and 15 th July 2020, to estimate the prevalence of IgG antibodies against 71 SARS-CoV-2 among adults using a sensitive and specific chemiluminescent microparticle 72 immunoassay (CMIA)-based test. Study design, setting, and participants 75 We conducted a cross-sectional seroprevalence study in District Srinagar over two weeks from 76 1 st July 2020 to 15 th July 2020. District Srinagar is a city in the valley of Kashmir in northern 77 India. It has an estimated adult (>18 years) population of just over one million. Study 78 participants were adults (>18 years) who visited select hospitals across the District during the 79 study period. We informed the participants of the study's purpose and procedure. We obtained written 82 informed consent from those who agreed to participate. The Institutional Ethics Committee of 83 Government Medical College Srinagar approved the study. Sample size 85 We estimated the minimum sample size needed based on an anticipated seroprevalence of 2% 86 within an absolute error of 0.8% with 95% confidence. We used a design effect of 2 to adjust for 87 the nature of sampling and increased the sample size further to account for a non-response of 88 20%. The minimum sample size needed for the study was 2821. We targeted a sample size of 89 3000. We deemed hospital-based selection of participants to be more convenient, rapid, and feasible, 98 given the constrained human resources and time available for completion of the study. Such a 99 choice could, however, lead to a non-representative sample. We made efforts to reduce this bias 100 by reporting age-and gender-standardized prevalence. We invited all adult patients (>18 years) coming to the selected hospitals during the study period 102 for participation in the study. testing. The samples were carefully packed in designated vaccine carriers to avoid hemolysis 123 during transportation. Laboratory procedure 125 We performed the test med using Fully Automated High Throughput Platform ARCHITECT figures for urban areas in the report to calculate weights for reporting age-and gender-152 standardized seroprevalence. The details are in the supplementary material (S1 Table) . To identify potential factors associated with SARS-CoV-2 seropositivity, we used logistic 154 regression analysis and reported unadjusted and age-and gender-adjusted odds ratio with a 95% 155 confidence interval. 156 We estimated the number of infections till two weeks before the study period, i.e., 15 th June 2020 157 to 30 th June 2020, by applying the age-and gender-specific seroprevalence rates found in the Table) . Over the study period, 3031 eligible persons were invited for participation in the study. The 165 refusal rate was 3.6% (108/3031). Two thousand nine hundred twenty-three blood samples were 166 collected, but demographic data was missing for 17 participants. We analyzed data from 2906 167 participants (Fig. 1) . Table) . 14 198 Young people, those with a history of ILI symptoms in the four weeks preceding the interview, 199 and those ever placed under quarantine were found to have significantly higher odds of the 200 presence of SARS-CoV-2 specific IgG antibodies (Table 5) . Table) . When adjusted for sensitivity and specificity of the laboratory test kit [14] , 207 the number of infections comes down to 32602 (95% CI 25470-39734) (S2 Table) . The cumulative number of RT-PCR confirmed cases till 15 th June 2020 was 538 in District 209 Srinagar, and the number was 932 till 30 th June 2020. The mid-interval (median) cumulative 210 number of RT-PCR confirmed cases in the two weeks preceding the study was 703 (Fig 2) . The . 255 We did not find any significant difference in seroprevalence among males and females (OR 1.2, 256 95% CI 0.8-1.8) ( and needs further investigation [31] . The presence of ILI symptoms in the recent past was the factor most strongly associated with the understanding the importance of this study and giving their time and consent for participation. the coronavirus disease (COVID-19) and the virus that causes it pdf?sfvrsn=adb3f72_2 310 3. 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Immunity and Ageing List of hospitals across District Srinagar Age and gender distribution of the population in District Srinagar and the 406 estimated population Estimated number of infections in District Srinagar Age-and gender-standardized seroprevalence