If you can’t measure it, you can’t improve it: Practical tools to assess ventilation and airflow patterns to reduce the risk for transmission of severe acute respiratory syndrome coronavirus 2 and other airborne pathogens

Particle counters can be used to measure clearance of aerosol particles generated in an enclosed space using a nebulizer, although such measurements may be less practical in most settings.10 Total volatile organic compounds provide an estimate of the chemical load in an indoor environment, and elevated levels may indicate insufficient ventilation.9 In private healthcare and elderly care facilities, total volatile organic compound levels correlated well with carbon dioxide levels, with elevated measurements in dental treatment rooms and general practitioner’s offices.9 In addition to ventilation, recent studies have highlighted the potential for patterns of airflow to contribute to long-distance dispersal of large and small droplets containing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).11–13 In a patient transport van with the ventilation fan on, smoke released by a smoke-emitting pen flowed from the front to the back of the van and airflow transported both large (212–250 µm diameter) and small (1–5 µm diameter) fluorescent microspheres >3 m to the back of the van.11 Contact tracing and sequencing demonstrated transmission of SARS-CoV-2 from 2 infected drivers to passengers in the back seat.11 Handheld smoke or fog generators provide a simple means to assess direction of airflow in enclosed spaces. [...]carbon dioxide levels increased to >4,000 ppm in a crowded movie theater with >90% occupancy, but only to a peak of 1,351 ppm in the same movie theater with 40% occupancy (Fig. 1C). [...]the adage, “If you can’t measure it, you can’t improve it,” applies to efforts to improve ventilation to reduce risk for transmission of SARS-CoV-2 and other respiratory pathogens.