Data_Sheet_1_Seroprevalence of SARS-CoV-2-specific anti-spike IgM, IgG, and anti-nucleocapsid IgG antibodies during the second wave of the pandemic: A population-based cross-sectional survey across Kashmir, India.docx

BackgroundWithin Kashmir, which is one of the topographically distinct areas in the Himalayan belt of India, a total of 2,236 cumulative deaths occurred by the end of the second wave. We aimed to conduct this population-based study in the age group of 7 years and above to estimate the seropositivity and its attributes in Kashmir valley.
MethodsWe conducted a community-based household-level cross-sectional study, with a multistage, population-stratified, probability-proportionate-to-size, cluster sampling method to select 400 participants from each of the 10 districts of Kashmir. We also selected a quota of healthcare workers, police personnel, and antenatal women from each of the districts. Households were selected from each cluster and all family members with age 7 years or more were invited to participate. Information was collected through a standardized questionnaire and entered into Epicollect 5 software. Trained healthcare personnel were assigned for collecting venous blood samples from each of the participants which were transferred and processed for immunological testing. Testing was done for the presence of SARS-CoV-2-specific anti-spike IgM, IgG antibodies, and anti-nucleocapsid IgG antibodies. Weighted seropositivity was estimated along with the adjustment done for the sensitivity and specificity of the test used.
FindingsThe data were collected from a total of 4,229 participants from the general population within the 10 districts of Kashmir. Our results showed that 84.84% (95% CI 84.51–85.18%) of the participants were seropositive in the weighted imputed data among the general population. In multiple logistic regression, the variables significantly affecting the seroprevalence were the age group 45–59 years (odds ratio of 0.73; 95% CI 0.67–0.78), self-reported history of comorbidity (odds ratio of 1.47; 95% CI 1.33–1.61), and positive vaccination history (odds ratio of 0.85; 95% CI 0.79–0.90) for anti-nucleocapsid IgG antibodies. The entire assessed variables showed a significant role during multiple logistic regression analysis for affecting IgM anti-spike antibodies with an odds ratio of 1.45 (95% CI 1.32–1.57) for age more than 60 years, 1.21 (95% CI 1.15–1.27) for the female gender, 0.87 (95% CI 0.82–0.92) for urban residents, 0.86 (95% CI 0.76–0.92) for self-reported comorbidity, and an odds ratio of 1.16 (95% CI 1.08–1.24) for a positive history of vaccination. The estimated infection fatality ratio was 0.033% (95% CI: 0.034–0.032%) between 22 May and 31 July 2021 against the seropositivity for IgM antibodies.
InterpretationDuring the second wave of the SARS-CoV-2 pandemic, 84.84% (95% CI 84.51–85.18%) of participants from this population-based cross-sectional sample were seropositive against SARS-CoV-2. Despite a comparatively lower number of cases reported and lower vaccination coverage in the region, our study found such high seropositivity across all age groups, which indicates the higher number of subclinical and less severe unnoticed caseload in the community.

【背景】克什米尔是印度喜马拉雅山脉地带中地形特征独特的区域之一，截至第二波疫情结束时，该地区累计新冠相关死亡病例共计2236例。本研究旨在针对7岁及以上人群开展一项基于人群的研究，以评估克什米尔河谷人群的血清阳性率及其相关影响因素。
【方法】本研究采用基于社区、户级别的横断面研究设计，通过多阶段、人群分层、按规模比例抽样的整群抽样方法，从克什米尔10个行政区中每个区招募400名参与者。同时，每个行政区额外按配额招募医护人员、警务人员及产前妇女。从每个整群中选取家庭，邀请所有7岁及以上的家庭成员参与研究。研究信息通过标准化问卷收集，并录入Epicollect 5软件。由经过培训的医护人员采集所有参与者的静脉血样，送检进行免疫学检测。检测项目包括新型冠状病毒（SARS-CoV-2）特异性抗刺突蛋白IgM抗体、IgG抗体以及抗核衣壳蛋白IgG抗体。本研究对加权血清阳性率进行了估算，并针对所用检测方法的灵敏度与特异度进行了校正。
【结果】本研究共从克什米尔10个行政区的普通人群中招募了4229名参与者。研究结果显示，在加权插补的普通人群数据中，84.84%（95%置信区间，Confidence Interval, CI：84.51%~85.18%）的参与者血清学检测呈阳性。针对抗核衣壳蛋白IgG抗体的多因素logistic回归分析显示，显著影响血清阳性率的变量包括：45~59岁年龄组（比值比，Odds Ratio, OR=0.73；95%CI：0.67~0.78）、自我报告合并症病史（OR=1.47；95%CI：1.33~1.61）以及疫苗接种史阳性（OR=0.85；95%CI：0.79~0.90）。针对抗刺突蛋白IgM抗体的多因素logistic回归分析显示，所有纳入评估的变量均对其存在显著影响：60岁以上年龄组OR=1.45（95%CI：1.32~1.57）、女性OR=1.21（95%CI：1.15~1.27）、城市居民OR=0.87（95%CI：0.82~0.92）、自我报告合并症OR=0.86（95%CI：0.76~0.92）、疫苗接种史阳性OR=1.16（95%CI：1.08~1.24）。以IgM抗体血清阳性率为参照，2021年5月22日至7月31日期间的估算感染病死率为0.033%（95%CI：0.032%~0.034%）。
【讨论】在SARS-CoV-2第二波疫情期间，本项基于人群的横断面研究样本中，84.84%（95%CI：84.51%~85.18%）的参与者抗SARS-CoV-2血清学检测呈阳性。尽管该地区报告的确诊病例数相对较少、疫苗接种覆盖率较低，但本研究仍在所有年龄组中发现了如此高的血清阳性率，这提示社区中存在大量未被发现的亚临床感染及轻症病例。