Background: Due to the substantial proportion of asymptomatic and mild courses many SARS-CoV-2 infections remain unreported. Therefore, assessment of seroprevalence may detect the real burden of disease. We aimed at determining and characterizing the rate of SARS-CoV-2 infections and the resulting immunity in a defined population. Methods: CoNAN is a population-based cohort study in the previously quarantined community Neustadt-am-Rennsteig, Germany six weeks after a SARS-CoV-2 outbreak with 49 cases identified by PCR screening of all 883 inhabitants. The primary objective of the study was to assess SARS-CoV-2 antibody seroconversion rate using six different IgG detecting immunoassays. Secondary objectives of the study were: i.) to determine the rate of seroconversion in children; ii.) to determine potential risk factors for symptomatic vs. asymptomatic Covid19 courses; iii.) to investigate the rate of virus persistence. Findings: We enrolled 626 participants (71% of the community population). All actual SARS-CoV-2 PCR tests were negative; while a total of 8.4% (52 of 620 tested) had antibodies against SARS-CoV-2 in at least two independent tests. Twenty of the antibody positive participants had previously a positive SARS-CoV-2 PCR. On the contrary, of those 38 participants with SARS-CoV-2 infection, only 20 (52.6%) were antibody positive. Interpretation: Several antibody tests conducted six weeks after an outbreak of SARS-CoV-2 did not detect all previously PCR-positive tested individuals. Cautious evaluation of antibody testing strategies to assess immunity against the infection is warranted.

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The Co‐HCW study is a prospective cohort study among hospital staff, including healthcare workers (HCWs) and administration staff, at the Jena University Hospital (JUH), Germany. The objectives of this study were to assess SARS‐CoV‐2 IgG seroprevalence, individual exposure risk factors and compliance of HCWs to wear personal protective equipment (PPE). After the first nosocomial COVID‐19 outbreak at JUH, mandatory masking was implemented on 20th March 2020. We evaluated point seroprevalence using two IgG detecting immunoassays and issued a questionnaire to assess COVID‐19 exposure, clinical symptoms and compliance to wear PPE. Antibody retesting was offered to participants with a divergent result of both immunoassays 5–10 weeks after the first test. Between 19th May and 19th June 2020, we analysed 660 participants [out of 3,228; 20.4%]. Among them, 212 participants (32.1%) had received a previous COVID‐19 test. Four of them (1.9%) reported a positive test result. After recruitment, 18 participants (2.7%) had SARS‐CoV‐2 antibodies in at least one immunoassay. Overall, 21 participants (3.2%) had any evidence of a past or current SARS‐CoV‐2 infection. Among them, 13 (61.9%) were not aware of direct COVID‐19 exposure and 9 (42.9%) did not report any clinical symptoms. COVID‐19 exposure at home (adjusted OR (aOR) with 95% CI: 47.82 (5.49, 416.62)) was associated with SARS‐CoV‐2 seroprevalence. We observed no evidence for an association between seroprevalence and exposure at work (aOR 0.48 (0.13, 1.70)) or with COVID‐19 risk area according to the working place (aOR for intermediate‐risk vs. high‐risk: 1.97 (0.42, 9.22), aOR for low‐risk versus high‐risk: 2.10 (0.40, 11.06); p = .655). Reported compliance of HCWs to wear PPE differed ( p < .001) between working in high‐risk (98.3%) and in intermediate‐risk areas (69.8%). In conclusion, compared to administration staff, we observed no additional risk to acquire SARS‐CoV‐2 infections by patient care, probably due to high compliance to wear PPE.