Summary
In 200 classrooms with real or sham HEPA purifiers, viruses showed up in 98.5% of week-long air samples. Purifiers did not lower the odds of high viral exposure (odds ratio 0.50, 95% confidence interval 0.08 to 3.25) but did modestly lower the number of virus types detected.
Key points
- Viruses were found in 524 of 532 week-long classroom air samples (98.5%), most often rhinovirus (89.5%).
- HEPA purifiers were not associated with lower odds of high viral exposure (odds ratio 0.50, 95% confidence interval 0.08 to 3.25).
- Purifiers were linked to a modest drop in the number of virus types detected.
- Humidity, grade, winter season and coarse particles were identified as risk factors for viral exposure.
- Design: secondary analysis of a blinded, cluster-randomized trial with real or sham HEPA units in 200 classrooms at 39 Northeastern US schools, 2015 to 2020; it measured virus in the air, not illness.
- Funding: NIAID (NIH) grants.