Risk of incident SARS-COV-2 infection among healthcare workers residing in Egyptian quarantine hospitals

Introduction: In response to the COVID-19 epidemic, Egypt established a unique care model based on quarantine hospitals where only externally-referred confirmed COVID-19 patients were admitted, and healthcare workers (HCWs) resided continuously over 1- to 2-week working shifts. Objectives: To estimate the risk of COVID-19 infection among HCWs in quarantine-hospital settings and assess the relative contribution of HCW-to-HCW (HtoH) and patient-to-HCW (PtoH) transmissions. Methods: Detailed longitudinal data was collected in two Egyptian healthcare facilities (hereafter denoted by Hosp1 and Hosp2), during the 2020 first wave of the COVID-19 epidemic (Hosp1: March 14th- August 1st;Hosp2: June 6th- July 11th). In both hospitals, only HCWs with no SARS-CoV-2 antibodies were allowed to start working shifts. During shifts, HCWs were tested using RT-PCR on nasopharyngeal swabs: i) routinely at the end of the shift, ii) upon symptoms, and iii) in case of outbreak suspicion (> 2 positive tests among HCWs). Using a stochastic compartmental model for the spread of SARS-CoV-2 in each hospital, we assessed the risk of SARS-CoV-2 acquisition overall and by transmission route (HtoH vs PtoH). We estimated the model parameters using Markov Chain Monte Carlo approaches. Results: Over a total follow-up of 6,601 person-days (PD), we estimated an incidence rate of 0.97 (95% CrI: 0.56-1.53) per 100 PD at Hosp1 and 8.98 (95% CrI: 3.81-17.75) per 100 PD at Hosp2. The probability for a HCW to be infected at the end of a shift was 12.8% (95% CrI: 7.6%-19.5%) for a 2-week shift at Hosp1, which lies within the range of risk levels previously documented in standard healthcare settings, whereas it was > threefold higher for a 7-day shift at Hosp2 (48.2%, 95%CrI: 23.8%-74.5%). Infection risk was mostly driven by HtoH transmission in both hospitals, although a substantial contribution from PtoH transmission was also found in Hosp2. Conclusion: The large variation in the infection risk found between the two quarantine hospitals we studied suggests that HCWs may face a high risk of infection, but that, with sufficient anticipation and infection control measures, especially those preventing patient-to-HCW transmission, this risk can be brought down to levels similar to those observed in standard healthcare settings.