Modelling the joint effects of single occupancy and N95 respirators on COVID-19 outbreaks in hospital wards.

Background: Outbreaks of respiratory pathogens on hospital wards present a major challenge for control of hospital-acquired infections. Structural controls such as single-occupancy patient rooms, or routine precautions such as the use of N95 respirators by healthcare staff can play an important role in preventing and mitigating outbreaks.

Methods: This study applies an agent-based extension of the Wells-Riley model of airborne pathogen exposure to simulate COVID-19 outbreaks on hospital wards. We simulated secondary attack rates and the sizes of outbreaks resulting from introduction of unrecognised cases in hospital wards with double- or single-occupancy patient rooms. We further simulated the impact of N95 respirator use by nurses during patient care activities, assuming an efficacy of 90% for protection and source control.

Results: The size of simulated outbreaks recorded at day 14 was markedly lower in wards with only single-occupancy rooms, compared to double-occupancy rooms (with means of 14.1 and 22.8 infections, respectively). Nurses were more likely to acquire infection than patients for both single- and double-occupancy scenarios. Single occupancy was associated with smaller outbreak sizes, with a larger relative impact on patients than staff. N95 respirators were effective at mitigating outbreaks, with higher impacts in wards with single-occupancy patient rooms.

Conclusions: Our results are consistent with claims that single-occupancy patient rooms reduce transmission of SARS-CoV-2 on hospital wards. Our findings also support the claim that use of N95 respirators by nurses when caring for patients can reduce the effective reproductive ratio of the pathogen. Finally, we demonstrated that switching to single occupancy can increase the benefit of N95 respirator use by healthcare staff.