Transmission dynamics and timing of key events for SARS-CoV-2 infection in healthcare workers

Background Healthcare workers (HCWs) have increased risk for SARS-CoV-2 infection via contacts in hospitals, as well as via transmission in the community. Serial interval, which is defined as the time between symptom onsets in an infector-infectee pair, and the incubation period are key parameters in determining the control strategies for COVID-19. This study aimed to evaluate surveillance of HCWs and estimate the serial interval and incubation period of COVID-19. Methods A total of 149 HCWs and 36 certain infector-infectee pairs between 19th March 2020 and 1st November 2020 in a university hospital were included in the study. Epidemiological characteristics were recorded. Serial interval and incubation period were estimated using parametric accelerated failure time models. Results Forty HCWs (26.8%) were detected via contact-based surveillance. Of 100 HCWs epidemiologically linked with a confirmed COVID-19 case, 36 (36%) had contact with a colleague. The median serial interval was 3.93 days (95% CI: 3.17-4.83). Of symptomatic HCWs, 97.5% had developed symptoms 13.71 (95% CI: 9.39-18.73) days after symptom onset of the primary case. The median incubation period was 3.99 (95% CI: 3.25-4.84) days. Of symptomatic HCWs, 97.5% developed symptoms within 9.49 (95% CI: 6.75-12.20) days after infection. Conclusions The serial interval and the incubation period of COVID-19 in HCWs were shorter than in the general population. Rigorous contact tracing and isolation of infected HCWs could have resulted in shorter serial intervals. Implementation of more stringent in-hospital control measures focussed on transmission between HCWs should be considered.