Serologic status and SARS COV-2 infection over 6-months of follow-up in healthcare workers in Chicago: A cohort study

John T. Wilkins*, Lisa R. Hirschhorn, Elizabeth L. Gray, Amisha Wallia, Mercedes Carnethon, Teresa R. Zembower, Joyce Ho, Benjamin J. DeYoung, Alex Zhu, Laura J. Rasmussen Torvik, Babafemi Taiwo, Charlesnika T. Evans

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


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.

Original languageEnglish (US)
JournalInfection Control and Hospital Epidemiology
StateAccepted/In press - 2021

ASJC Scopus subject areas

  • Epidemiology
  • Microbiology (medical)
  • Infectious Diseases


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