Assessing the risk of exposure to SARS-CoV-2 of healthcare workers in Hong Kong : an environmental surveillance and sero-epidemiological study

Abstract

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has laid a huge burden on the healthcare systems that are challenged during waves of outbreaks globally. It is important to access the exposure risk to SARS-CoV-2 in healthcare settings to better protect our healthcare workers and avoid the breakdown of healthcare systems. There are two major sources of contamination – one is from COVID-19 inpatient; one is from the asymptomatic or pre-symptomatic outpatients seeking medical help. To access the exposure risk to SARS-CoV-2 in inpatient and outpatient facilities in Hong Kong, a longitudinal environmental surveillance was done in Accident and Emergency Department (A&E) and isolation wards of a teaching hospital in Hong Kong during April 2020 to April 2021 and March to May 2022, with a sero-epidemiological study for hospital workers conducted during January to April 2021.

During the study period, the contamination level remained low in the A&E regardless the change in epidemic, with an overall surface and air positive rates of 0.703% and 1.25%, respectively. A zero seroprevalence observed in healthcare workers supported the low risk of exposure, which also showed the successful implementation of infection control measures in limiting the contamination from community sources. In contrast, higher surface positive rates were observed in isolation wards with surface positive rate of 14.1%, 8.33% and 4.29% in patients’ room, anterooms, and nursing station, respectively. An overall air positive rate in patients’ room of isolation ward was 9.33%. It shows the infection control measures taken in isolation wards were able to reduce the contamination brought out from the patients’ rooms. The differences in contamination level in the A&E and isolation wards suggest a possible need to further improve the infection control measures and/or the practices of healthcare workers at the isolation wards.

Logistic regression was used in investigating the factors associated with the detection of SARS-CoV-2 in the A&E and isolation wards. In the A&E, increased weekly attendance and afternoon sampling sessions (eg. sampled after longer hours post cleaning) were found associated with the increased detection of SARS-CoV-2 in surface, indicating an increase in frequency of cleaning is needed, especially with an increase in attendance. In isolation wards, lower CT values of patients’ respiratory specimens (eg. higher viral load) was associated with detection of SARS-CoV-2 in air. Interestingly, the use of different types of non-invasive ventilation was not associated with viral RNA detection in air. Distinct factors were associated with detection of SARS-CoV-2 from surfaces that were routinely cleansed and non-routinely cleansed (eg. pillows). Specifically, higher CT values (eg. lower viral load) and samples collected at later days post-symptom onset were associated with detection from routinely cleansed surfaces, while high-touch surfaces and longer days of hospitalization (proxy for longer duration of viral shedding) were associated with detection on non-routinely cleansed surfaces. These results suggest that routine cleansing may be effective to remove contamination from high-touch surfaces while extended stay at the isolation ward may increase the contamination risk. These findings provide information in improving the infection control measures in hospitals.