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[Preprint]. 2021 Apr 19:2021.04.12.21255324. [Version 1] doi: 10.1101/2021.04.12.21255324

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Figure 1. — Seropositive health care workers by study visit in relation to SARS-CoV-circulation in Philadelphia. (A) Number of positive COVID-19 tests in Philadelphia from March 2020 – February 2021 (data retrieved from opendataphilly.org on 9 March 2021). The first viral period is defined as infections that occurred before July 2, 2020 and the second viral period as infections that occurred after July 2, 2020. (B) Number of health care workers tested by serum collection date, stratified by study visit and seropositivity status. One out of the 9 health care workers with a positive NP SARS-CoV-2 PCR test outside of our study seroconverted after 2 July 2020 and their seropositive sample is therefore not shown in this graph. (C) Seropositive health care workers (n=55) by study visit. The majority of health care workers (n=1988) were seronegative throughout the study period.