With WHO publishing a consultation report on updated terminologies, a shift in focus from Pathogen Droplets to Aerosolized Pathogens, and healthcare facilities throughout the world implementing new strategies to take into account Air Changes per Hour (ACH).
The SARS-CoV-2 pandemic has bought onto mind a new mindset in preventing their transmission. Since many viruses, including SARS-CoV-2, are capable of becoming aerosolized, this puts anyone nearby at risk of infection from any aerosolized pathogens. Of course, this depends on the dosage of said pathogen, which differs depending on the pathogen. As of 2026, the US is currently concerned with 3 commonly aerosolized pathogens. SARS-CoV-2, measles, and the seasonal flu.
One of the best ways to prevent this is optimal ventilation, which is measured by Air Changes per Hour (ACH). According to the CDC, it takes at least 4.6 ACH in order to clear 99% pathogens in a room, and 6.9 ACH to clear 99.9% of pathogens. This is, of course, dependent how how even air circulation in a room is. Indoor ACH is typically achieved through High-Efficiency Air (HEPA) filters, Germicidal UV-C lights, or air purifiers.
It is recommended that Healthcare facilities have at minimum, an ACH of 6 to 15 (depending on the purpose of the room). Procedural rooms would, for example, need to have at least 15 ACH. The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) also has shared their own guidelines for the control of infectious aerosols.
Read the whole article, and find the various sources, here at Infection Control Today.
Read the WHO article regarding the updated terminology here.
