‘Portable air cleaners aimed at curbing indoor spread of infections are rarely tested for how well they protect people – and very few studies evaluate their potentially harmful effects. That’s the upshot of a detailed review of nearly 700 studies that we co-authored in the journal Annals of Internal Medicine.
Many respiratory viruses, such as COVID-19 and influenza, can spread through indoor air. Technologies such as HEPA filters, ultraviolet light and special ventilation designs – collectively known as engineering infection controls – are intended to clean indoor air and prevent viruses and other disease-causing pathogens from spreading.
Along with our colleagues across three academic institutions and two government science agencies, we identified and analyzed every research study evaluating the effectiveness of these technologies published from the 1920s through 2023 – 672 of them in total.
These studies assessed performance in three main ways: Some measured whether the interventions reduced infections in people; others used animals such as guinea pigs or mice; and the rest took air samples to determine whether the devices reduced the number of small particles or microbes in the air. Only about 8% of the studies tested effectiveness on people, while over 90% tested the devices in unoccupied spaces.
We found substantial variation across different technologies. For example, 44 studies examined an air cleaning process called photocatalytic oxidation, which produces chemicals that kill microbes, but only one of those tested whether the technology prevented infections in people….’
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