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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.
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.