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Serologic Status and SARS CoV-2 Infection over 6-Months of Follow-Up in Healthcare Workers in Chicago: A Cohort Study.

Wilkins JT, Hirschhorn LR, Gray EL, Wallia A, Carnethon M, Zembower TR, Ho J, DeYoung BJ, Zhu A, Torvik LJR, Taiwo B, Evans CT. Serologic Status and SARS CoV-2 Infection over 6-Months of Follow-Up in Healthcare Workers in Chicago: A Cohort Study. Infection control and hospital epidemiology. 2021 Aug 9; 1-29.

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OBJECTIVE: To determine the changes in SARS-CoV-2 serologic status and SARS-CoV-2 infection rates in healthcare workers (HCW) over 6-months of follow-up. DESIGN: Prospective cohort study. SETTING AND PARTICIPANTS: HCW in the Chicago area, USA. METHODS: Cohort participants were recruited in May/June 2020 for baseline serology testing (Abbott anti-Nucleocapsid IgG) and were then invited for follow-up serology testing 6 months later. Participants completed monthly online surveys which assessed demographics, medical history, COVID-19 illness, and exposures to SARS-CoV-2. The electronic medical record was used to identify SARS-CoV-2 PCR positivity during follow-up. Serologic conversion and SARS-CoV-2 infection or possible reinfection rates (cases per 10,000 person*days) by antibody status at baseline and follow-up were assessed. RESULTS: 6510 HCW were followed for a total of 1,285,395 person*days (median follow-up, 216 days). For participants who had baseline and follow-up serology checked, 285 (6.1%) of the 4681 seronegative participants at baseline seroconverted to positive at follow-up; 138 (48%) of the 263 who were seropositive at baseline were seronegative at follow-up. When analyzed by baseline serostatus alone, 519 (8.4%) of 6194 baseline seronegative cohort participants had a positive PCR after baseline serology testing (rate = 4.25/10,000 person days). Of 316 participants who were seropositive at baseline, 8 (2.5%) met criteria for possible SARS-CoV-2 reinfection (PCR+ more than 90 days after baseline serology) during follow-up representing a rate of 1.27/10,000 days at risk. The adjusted rate ratio for possible reinfection in baseline seropositive compared to infection in baseline seronegative participants was 0.26, (95%CI: 0.13 - 0.53). CONCLUSIONS: Seropositivity in HCWs is associated with moderate protection from future SARS-CoV-2 infection.

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