Understanding nosocomial influenza transmission in acute- and chronic-care wards using an agent-based model

Nosocomial influenza remains a major challenge in hospital settings. However, the effects of activities of daily living (ADL)-based care dependency, healthcare worker (HCW) contact structure, community importation, and near- and far-field exposure pathways on ward-level transmission remain unclear. We therefore used an agent-based model to investigate influenza transmission dynamics in acute- and chronic-care wards and to evaluate the relative contribution of ADL-based HCW contact and airborne exposure pathways.

The agent-based model of nosocomial influenza transmission incorporated community importation, ward structure, ventilation, nurse shift schedules, symptomatic and asymptomatic/presymptomatic infection pathways, ADL-based patient-HCW contact patterns, and near- and far-field exposures. Simulations were performed over 1 year, with 1,000 stochastic iterations performed for each scenario. Intervention strategies included no isolation, prophylaxis alone, isolation, and isolation with prophylaxis.

Chronic-care wards had a higher nosocomial infection burden and more HCW-contact-associated patient infections, whereas the acute-care ward showed more frequent patient turnover and more community-associated imported infections. Isolation-based interventions reduced nosocomial and HCW-contact-associated patient infections more clearly than did prophylaxis alone, although residual HCW-contact-associated infections under isolation-based scenarios were linked to asymptomatic/presymptomatic HCWs. Far-field-only infections were uncommon.

Chronic-care wards may be particularly vulnerable to nosocomial influenza transmission following viral introduction, as greater care dependency may increase opportunities for HCW-patient transmission. Mathematical modelling provides a useful approach for identifying otherwise unobservable transmission mechanisms and highlights the importance of symptomatic isolation, asymptomatic/presymptomatic transmission, and exposure pathways in hospital influenza control.