Interventions to control nosocomial transmission of SARS-CoV-2: a modelling study

Pham, T. M.; Tahir, H.; van de Wijgert, J. H.; Van der Roest, B.; Ellerbroek, P.; Bonten, M. J.; Bootsma, M. C.; Kretzschmar, M. E.

Background: Emergence of more transmissible SARS-CoV-2 variants requires more efficient control measures to limit nosocomial transmission and maintain healthcare capacities during pandemic waves. The relative importance of different strategies is unknown. Methods: We developed an agent-based model and compared the impact of personal protective equipment (PPE), screening of healthcare workers (HCWs), contact tracing of symptomatic HCWs, and HCW cohorting on nosocomial SARS-CoV-2 transmission. The model was fit on hospital data, assuming 90% effective PPE use in COVID-19 wards. Intervention effects on the effective reproduction number (R), HCW absenteeism and the proportion of infected individuals among tested individuals (positivity rate) were estimated for a more transmissible variant. Findings: Introduction of a variant with 56% higher transmissibility increased - all other variables kept constant - R from 0.4 to 0.65 (+63%) and nosocomial transmissions by 303%, mainly because of more transmissions caused by pre-symptomatic patients and HCWs. Compared to baseline, PPE use in all hospital wards (assuming 90% effectiveness) reduced R by 85% and absenteeism by 57%. Screening HCWs every three days with perfect test sensitivity reduced R by 67%, yielding a maximum test positivity rate of 5%. Screening HCWs every three or seven days assuming time-varying test sensitivities reduced R by 9% and 3%, respectively. Contact tracing reduced R by at least 32% and achieved higher test positivity rates than screening interventions. HCW cohorting reduced R by 5%. Interpretation: PPE use in all hospital wards and regular screening of HCWs seem most effective in preventing nosocomial transmissions of SARS-CoV-2 variants with higher transmissibility.