Any employee who was working in hospital premises with or without direct patient contact was included as a HCW. This included individuals employed directly by the hospital or via a company in contract with the hospital. All HCWs – both clinical and non-clinical, were tested if any of the following symptoms were present- fever, cough, sore throat, body ache, headache, vomiting and diarrhoea; or if re-joining work after a leave of more than 14 days. Testing was done with a nasopharyngeal swab for SARS-CoV-2 RT-PCR by an ICMR approved kit having 99% sensitivity and specificity. Healthcare workers were encouraged to self-test, if required under supervision to minimize exposure to other HCWs. Self-collection has been found to be an appropriate and reliable alternative to HCW collection [3,4]. Awaiting results, HCWs were sent for home isolation or quarantined in the hospital staff quarters. Healthcare workers that tested positive were evaluated by a member of the hospital infection control committee (HICC) for contact tracing. Those at high risk exposure (exposure >15 min without mask, less than a meter distance) were quarantined for 14 days with a repeat SARS-CoV-2 RTPCR done on day 12 or 13 before re-joining work [5]. All positive HCWs followed Municipal Corporation of Greater Mumbai (MCGM) guidelines for home or institutional quarantine and re-joined work after testing negative for SARS-CoV-2. Once travel restrictions were lifted, details of travel i.e.; self-driven vs public transport were documented at the time of contact tracing. The virology laboratory data of HCWs tested and HICC team data for category of staff and contact tracing from March, 2020 to August, 2020 was retrospectively analysed after approval. Exposure was defined as hospital exposure when there was contact with a SARS-CoV-2 positive patient or staff in hospital premises and for individuals working in areas of the hospital like Emergency room, radiology etc. where exposure to SARS-CoV-2 unknown status is high, and community exposure was defined as any HCW who was SARS-CoV-2 positive with history of exposure to SARS-CoV-2 in the community including family members and during travel. Exposure was consi-dered likely community acquired if there was no exposure to SARS-CoV-2 positive or unknown status patient without breach in social distancing measures with colleagues. Home leave was defined as leave from work for more than 14 days and new employees. Hostel exposure included nurses who were residing in the hostel and also staff who preferred not going home during the pandemic and were residing in hospital quarters. Individuals exposed to positive staff residing in the same room/flat were considered as high risk exposure.

Personal protective equipment (PPE) donning and doffing training was carried out for HCWs. PPE use was decided based on location and risk category as per Ministry of Health and Family Welfare (MOHFW) guidelines [6]. As the pandemic progressed and we learnt more about the transmission dynamics, changes were made to infection control protocols and staff were briefed about it.

Five hundred and thirty four HCWs were tested during 6 months with 42 HCWs (8%) positive for SARS-CoV-2 without any fatalities. The monthly incidence of SARS-CoV-2 positivity in HCWs is depicted in Fig. 1. Peak incidence of cases in Mumbai was seen in June [7]. Cases in HCWs rose and fell parallel to community incidence.

Fig. 1 Healthcare workers tested Monthly for SARS-CoV-2 in the first six months of the pandemic.

Nurses had the highest incidence of SARS-CoV-2 positivity; 13 out of 42 (31%) although only 3 out of 13 (23%) had direct high risk patient exposure in the emergency room and day care unit (Fig. 2). Fourteen percent (6 out of 42) positive cases were seen in cafeteria and human resource personnel. Clustering of cases was seen in blood bank and amongst laboratory technicians. Doctors were least positive in our cohort (2 out of 42).

Number of staff positive in brackets. HR-Human resources personnel

Fig. 2 Percentage positivity in the category of staff tested.

Almost 70% (29 out of 42) of the positive cases had no high risk exposure in the hospital and were classified as likely community acquired (Fig. 3). Amongst high risk exposure areas- day care area, suspected and positive COVID ward, and COVID ICU had the least SARS-CoV-2 positivity. No doctor or nursing staff working in COVID wards or ICU tested positive for SARS-CoV-2. After a nursing staff tested positive in day care area, PPE used while managing day care patients was modified with no further cases noted. Two nursing staff working in the emergency room tested SARS-CoV-2 positive.

Fig. 3 Likely source of SARS-CoV-2 transmission to healthcare workers.

Amongst positive staff with likely community acquired transmission (Fig. 3), 21% (4 out of 19) had history of SARS-CoV-2 positive contact and 37% (7 out of 19) travelled by public transport. Nearly one fourth of SARS-CoV-2 positive staff were returning from home leave (10 out of 42) and almost all were asymptomatic at the time of testing (Fig. 3).

The present study analyses the transmission dynamics of the first HCW cohort from India. In a pediatric cohort, risk of asymptomatic SARS-CoV-2 carriage is com-pounded by presence of caregivers. Other risk factors for HCW exposure include inadequate social distancing between employees and non-compliance of mask wearing during breaks [8].

Ethics approval: IEC, SRCC-CH; R-202019, November, 2020.

Contributors: AP, SU: designed the retrospective study and wrote the manuscript; MB: wrote the contact tracing guidelines for HCWs; SS, SK: were involved in testing and tracing positive HCWs. All authors approved the final version of manuscript, and are accountable for all aspects related to the study.

Funding: None; Competing interests: None stated.