Modelling the synergy between single-occupancy and PPE in controlling COVID-19 outbreaks on hospital wards

BackgroundOutbreaks of respiratory pathogens on hospital wards present a major challenge for control of hospital-acquired infections. When illness presentation is mild or infection is asymptomatic, isolation of recognised cases may be insufficient to prevent outbreaks, as unrecognised cases may be common. In such scenarios, structural controls such as the design of wards with 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. MethodsThis 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 the impact of single-vs. double-occupancy patient rooms on secondary attack rates and the sizes of outbreaks resulting from introduction of unrecognised cases. 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. ResultsIn our simulations, the size of outbreaks recorded at day 14 was markedly lower in wards with only single-occupancy rooms, compared to double-occupancy rooms (with means of 15.2 and 25.1 infections, respectively). We found that nurses working on wards were more likely to acquire infection than patients. Higher patient room occupancy was associated with increased outbreak size, 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. ConclusionsSingle-occupancy rooms can greatly decrease the risk of hospital acquired airborne infection for patients. We show that single-occupancy hospital rooms can also reduce the number of healthcare workers infected during an outbreak of an airborne respiratory virus, but not to the same relative extent as patients. Due to the structural constraints limiting transmission between patients in different rooms, outbreaks were driven by transmission events involving nurses, which were effectively mitigated through the use of N95 respirators. Taken together, our results suggest that single-occupancy rooms are effective at reducing outbreak sizes. However, they are insufficient by themselves to prevent large outbreaks without mitigation efforts focused on limiting the potential for transmission involving healthcare workers, such as the use of N95 respirators.