LAUSR

Background We examined SARS-CoV-2 seroconversion incidence and its risk factors 21 days after baseline screening among healthcare workers(HCWs) in a resource-limited setting. Methods A prospective cohort study of 4040 HCWs took place between April and June 2020 at 12 university healthcare facilities in Cairo, Egypt. Follow-up exposure and clinical data were collected using an online survey. SARS-CoV-2 testing was done using rapid IgM and IgG serological tests; RT-PCR was done for those with positive serology. Cox proportional hazards modelling was used to estimate adjusted hazard ratios(HR) of seroconversion. Results Of the 3870/4040(95.8%) HCWs who tested negative for IgM, IgG, and PCR at baseline, 2282(59.0%) returned for follow-up. Seroconversion incidence (positive IgM and/or IgG) was 100/2282(4.4%,95%:CI:3.6-5.3),mostly asymptomatic(64/100,64.0%), with a daily hazard = 0.21%(95%-CI:0.17-0.25)/48746 person-days of follow-up. Seroconversion was 4.0%(64/1596;95%CI:3.1-5.1) among asymptomatic and 5.3%(36/686;95%CI:3.7-7.2) among symptomatic HCWs. Seroconversion was independently associated with older age(HR:2.71,95%CI:1.31-5.58); lower education(HR:3.89,95%CI:1.89-8.00); contact with a confirmed case>15 minutes(HR:2.20,95%CI:1.18-4.10); chronic kidney disease(HR:4.42,95%CI:1.03-18.96); pregnancy(HR:3.5,95%CI:1.05-11.85); change/loss of smell(HR:3.17,95%CI:1.48-6.78); and negatively associated with contact at workplace(HR:0.48,95%CI:0.28-0.82). Conclusions Most seroconversions were asymptomatic, emphasizing the need for regular universal testing. Seropositivity was three-fold that observed at baseline. Cumulative infections increased nationally by a similar rate, suggesting that HCWs’ infections reflect community not nosocomial transmission during the first wave of COVID-19 epidemic in Egypt.