Field evaluation of exhaust-fan and air-flow pathway constraint retrofits to reduce contaminated air dispersion in hospitals

• Tracer gas measurements verified transport of contaminants between hospital spaces • Simple air flow control and flow barriers can lower airborne transmission risk • Exhaust fans and door partitions reduced contaminant transfer by ∼30 fold • Wells–Riley modelling showed infection probability fell below 4% in adjacent rooms • Adding exhaust fans and room doors provide rapid alternatives to isolation rooms Constraining and controlling the flow of air between building spaces represents a promising, inexpensive and adaptable method for reducing the risk of transmission of airborne infections in hospitals, particularly during outbreaks when provision of negative pressure isolation rooms for all patients is not feasible. Here we demonstrate the effectiveness of retrofits made to hospital rooms where exhaust fans and sliding doors were installed to control the airflow and prevent fugitive air from a potentially index patient room to the surrounding hospital spaces. This is done with measurements of tracer gas concentrations in an existing hospital for a range of door opening and fan operational configurations. While individually the two types of retrofits were not adequate to completely eliminate the flow of contaminants between spaces, in combination they resulted in a 30-fold reduction in tracer gas concentrations compared to the non-retrofitted case. Door opening width and fan speed tests confirmed the importance of these interventions in reducing inter-space transfer of contaminants. Infection risk modelling showed significant reductions in the probability of infection when a highly emitting patient was located in the index room. In this case, under certain typical inhalation rates and high quanta emission risk modelling assumptions, operating the exhaust fan with the index patient room door closed, reduced the probability of infection of a susceptible patient in an adjacent room from greater than 30% to less than 3% as a result of 24-hours of exposure, and for staff in the corridor from approximately 60% to 2% after 12 hours.