AS&T Highlight: Detection of SARS-CoV-2 RNA on air purifier filters in university spaces without symptomatic or confirmed cases

By Jenna Ditto, Washington University in St. Louis

Article by: Jing Li, Merel Bot, Xinlei Liu, Yuan Yao, Roel A. Ophoff & Yifang Zhu (2026) Detection of SARS-CoV-2 RNA on air purifier filters in university spaces without symptomatic or confirmed cases, Aerosol Science and Technology, 60:5, 440-449, DOI: 10.1080/02786826.2025.2601887.

This recent study by Li et al. investigated the presence of airborne SARS-CoV-2 in several university spaces. The authors tracked the virus on air purifier filters collected from three room types within a single university building. A key distinguishing aspect of this study, compared to other similar studies measuring airborne SARS-CoV-2 presence in healthcare settings or settings with known positive-testing individuals, is that no known symptomatic or confirmed-positive individuals were present in these university spaces during the sampling efforts.

In this study, the team sought to assess the presence of SARS-CoV-2, respiratory syncytial virus (RSV), and influenza A on air purifier filters from fall 2022 to summer 2023. Notably, in the fall-winter 2022 period, many regions in the United States experienced a “tripledemic”, meaning that while COVID-19 cases remained high, RSV and influenza A cases rose substantially relative to their lower levels during the peak of the COVID-19 pandemic.

This work aimed to first examine indoor environments for the presence of SARS-CoV-2 in the post-pandemic period and, second, to investigate the co-occurrence of two other prominent airborne viruses, RSV and influenza A, in indoor air. To accomplish these aims, the authors collected filters from Blueair purifiers installed in one community room, five conference rooms, and eight classrooms in a university building. They used reverse transcription quantitative polymerase chain reaction (RT-qPCR) to detect viral genetic material in their air filter samples.

Overall, they found a 21% SARS-CoV-2 RNA positive rate across their fall-winter, spring, and summer sampling periods (with the seasonal effect not a statistically significant driver on the SARS-CoV-2 RNA positive rate). They found a 15% positive rate in classrooms, 43% in the community room, and 43% in the conference rooms. The differences between these room types were statistically significant overall, though no pairwise comparisons between room types were significant. In contrast, RSV was found in only 2% of samples, and influenza A in only 4% overall.

The team also found that viral RNA concentrations were significantly higher in fall-winter than in summer. However, this difference was no longer significant once the authors normalized for sampling duration.

The authors emphasized the importance of future work that characterizes both detection rates and viral concentrations to gain a full understanding of airborne transmission in real, occupied indoor spaces. Overall, this study reinforces our understanding of SARS-CoV-2’s airborne transmission, even in non-healthcare settings without known confirmed-positive individuals, and demonstrates the use of air filters as a tool to track viral aerosol material in diverse indoor environments.