Detection of SARS-CoV-2 RNA on air purifier filters in university spaceswithout symptomatic or confirmed cases
Application: Indoor Air Surveillance | Respiratory Virus Detection | Environmental Monitoring
Technology: Nanotrap® Microbiome A Particles
Publication: Li J, Bot M, Liu X, Yao Y, Ophoff RA, Zhu Y. Detection of SARS-CoV-2 RNA on air purifier filters in university spaces without symptomatic or confirmed cases. Aerosol Science and Technology. 2026;60(5):440–449.
Overview
A peer-reviewed study led by researchers at the University of California, Los Angeles (UCLA) demonstrates the potential of air purifier filters combined with Nanotrap® technology to detect respiratory viruses in shared indoor environments, even when no symptomatic or confirmed COVID-19 cases are known to be present.
Published in Aerosol Science and Technology, the study examined high-efficiency particulate air (HEPA) filters collected from classrooms, conference rooms, and a community room at UCLA between September 2022 and October 2023.
Researchers used Nanotrap Microbiome A Particles from Ceres Nanosciences to concentrate viral material recovered from the filters before RNA extraction and RT-qPCR analysis.
SARS-CoV-2 RNA was detected in 21% of the 127 samples included in the final analysis, despite the absence of known symptomatic or confirmed cases in the sampled spaces. Viral RNA was detected across all three sampling periods and room types, highlighting the potential for environmental monitoring to reveal otherwise unrecognized respiratory virus circulation.
The findings demonstrate a promising application of Nanotrap-enabled sample preparation for indoor air surveillance and reinforce the importance of sensitive viral detection methods in shared environments.
Study Highlights
Detection without known cases: SARS-CoV-2 RNA was detected in 21% (27/127) of analyzed filter samples from university spaces without known symptomatic or confirmed COVID-19 cases.
Multiple indoor environments: Researchers examined HEPA filters from eight classrooms, five conference rooms, and one community room.
Year-round viral detection: SARS-CoV-2 RNA was detected during fall-winter, spring, and summer sampling periods, suggesting continued viral circulation throughout the year.
Differences by room type: Detection rates were 43% in conference rooms and the community room, compared with 15% in classrooms.
Higher viral RNA levels in fall-winter: Among positive samples, SARS-CoV-2 RNA concentrations were significantly higher during fall-winter than summer.
Multi-pathogen detection: Researchers also detected influenza A virus and respiratory syncytial virus (RSV), although at substantially lower frequencies than SARS-CoV-2.
Nanotrap-enabled sample preparation: Nanotrap Microbiome A Particles were used to concentrate viral RNA from HEPA filter eluates prior to nucleic acid extraction and molecular analysis.
Nanotrap Technology in Action
Researchers collected HEPA filters from portable air purifiers deployed throughout the UCLA Fielding School of Public Health.
The filters accumulated airborne particles during routine operation over sampling periods lasting approximately three to six months, providing a means of assessing viral material present in shared indoor environments.
To recover viral material, sections of each filter were eluted in phosphate-buffered saline (PBS). A 10 mL portion of the resulting eluate was then processed using Nanotrap Microbiome A Particles, followed by RNA extraction using the NucleoMag DNA/RNA Water kit from Macherey-Nagel.
Extracted RNA was analyzed using RT-qPCR assays targeting SARS-CoV-2, RSV, and influenza A virus.
The study incorporated bovine coronavirus as a process control to assess sample recovery and extraction quality. Samples with recovery efficiencies below 1% were excluded, leaving 127 samples for final analysis.
Among retained samples, the median bovine coronavirus recovery efficiency was 65%, demonstrating measurable process recovery within the workflow.
The successful detection of respiratory viral RNA from HEPA filter eluates illustrates the applicability of Nanotrap technology to an environmental sample type beyond conventional wastewater and liquid-based surveillance.
Importantly, the study was not designed to compare Nanotrap technology against alternative concentration methods. Rather, it demonstrates the practical incorporation of Nanotrap particles into an indoor air monitoring workflow.
Key Findings
Performance Measure | Study Finding |
Total filter subsamples prepared | 161 |
Samples included after quality control | 127 |
SARS-CoV-2 RNA detection | 21% (27/127) |
SARS-CoV-2 detection in classrooms | 15% |
SARS-CoV-2 detection in conference rooms | 43% |
SARS-CoV-2 detection in community room | 43% |
RSV RNA detection | 2% |
Influenza A RNA detection | 4% |
SARS-CoV-2 RNA levels in positive samples | 23–471 gene copies per sample |
Median process-control recovery | 65% |
SARS-CoV-2 RNA concentrations in positive samples ranged from 23 to 471 gene copies per filter subsample, with a median of 118 gene copies.
Although SARS-CoV-2 detection rates did not differ significantly across sampling periods, viral RNA concentrations were significantly higher during fall-winter compared with summer.
The detection of SARS-CoV-2 RNA in all three room types and throughout the study period provides additional evidence that respiratory viral material can accumulate in shared indoor environments even when infections are not clinically recognized.
Significance
This study highlights an emerging opportunity to extend environmental pathogen surveillance beyond wastewater into indoor air monitoring.
Traditional respiratory disease surveillance relies heavily on clinical testing and the reporting of symptomatic infections. However, asymptomatic and presymptomatic individuals may contribute to viral circulation without being identified through conventional surveillance systems.
By analyzing material collected on existing HEPA air purifier filters, researchers demonstrated a potential approach for detecting respiratory viral RNA in occupied indoor environments without requiring direct sampling from individuals.
The use of Nanotrap Microbiome Particles in the sample preparation workflow illustrates the versatility of particle-based concentration technology across environmental matrices.
While additional research is needed to establish standardized sampling intervals, optimize recovery, and determine how filter-based viral measurements relate to infection risk, these findings suggest opportunities for environmental monitoring in universities, schools, workplaces, and other shared indoor spaces.
Importantly, detecting viral RNA does not establish the presence of infectious virus or confirm active transmission. Nevertheless, molecular detection from air purifier filters may provide useful complementary information for understanding respiratory pathogen circulation.
This research expands the demonstrated applications of Nanotrap technology and highlights the potential for sensitive environmental surveillance to reveal respiratory viral signals that may otherwise go undetected.
SKU 44XXX
Comments