Evidence-based aerosol clearance times in a healthcare environment

Abstract

Background: As researchers race to understand the nature of COVID-19 transmission, healthcare institutions must treat COVID-19 patients while also safeguarding the health of staff and other patients. One aspect of this process involves mitigating aerosol transmission of the SARS-CoV2 virus. The U.S. Centers for Disease Control and Prevention (CDC) provides general guidance on airborne contaminant removal, but directly measuring aerosol clearance in clinical rooms provides empirical evidence to guide clinical procedure.

Aim: We present a risk-assessment approach to empirically measuring and certifying the aerosol clearance time (ACT) in operating and procedure rooms to improve hospital efficiency while also mitigating the risk of nosocomial infection.

Methods: Rooms were clustered based on physical and procedural parameters. Sample rooms from each cluster were randomly selected and tested by challenging the room with aerosol and monitoring aerosolized particle concentration until 99.9% clearance was achieved. Data quality was analysed and aerosol clearance times for each cluster were determined.

Findings: Of the 521 operating and procedure rooms considered, 449 (86%) were issued a decrease in clearance time relative to CDC guidance, 32 (6%) had their clearance times increased, and 40 (8%) remained at guidance. The average clearance time change of all rooms assessed was a net reduction of 27.8%.

Conclusion: The process described here balances the need for high-quality, repeatable data with the burden of testing in a functioning clinical setting. Implementation of this approach resulted in a reduction in clearance times for most clinical rooms, thereby improving hospital efficiency while also safeguarding patients and staff.

Keywords: Aerosol; COVID-19.

Figure 1

Example flowchart of room cluster breakdown. “ACH” stands for “air changes per hour.”

Figure 2

Aerosol clearance test procedure.

Figure 3

Comparison of time distributions for tested rooms to achieve 99.9% aerosol clearance.

Figure 4

Impact of ACT testing on all rooms certified by this method. The y=x line is overlayed to indicate where measurements would lie in the event of perfect alignment with CDC guidance. The average reduction in ACT for rooms grouped according to CDC guidance-based ACTs is noted at the top of the graph.

Figure 5

Sample aerosol clearance measurement data plot. The 99.9% clearance threshold was calculated with consideration of the background particle concentration measured prior to the simulated AGP event. Error bars represent the ±15% uncertainty of the CPCs.