SARS-CoV-2 Detection in Heating, Ventilation, and Air Conditioning Filters of University Lecture Rooms

The COVID-19 pandemic has highlighted the need for effective environmental surveillance tools to monitor respiratory viruses in public spaces, particularly in indoor congregation areas. This study evaluated the potential of using heating, ventilation, and air conditioning (HVAC) filters to detect the presence of SARS-CoV-2 in university lecture rooms. HVAC filters were collected from three air handling units (AHUs) in university buildings between November 2022 and February 2024. Using vacuum-based dust collection, followed by RT-ddPCR analysis, varying levels of SARS-CoV-2 were detected on filters across AHUs. Positive detection rates ranged from 28 to 86% in prefilters and 17–50% in final filters. Viral concentrations in coarse dust varied significantly across AHUs and sampling batches, reaching up to 14,000 genome copies (gc)/g of dust in prefilters. Analysis of fine dust samples showed viral concentrations higher than those of coarse dust when normalized by dust mass. Factors such as the prevalence of COVID-19 on campus, occupancy dynamics, lecture room air distribution systems, and HVAC operation conditions likely contributed to the observed SARS-CoV-2 positive rates and concentrations in dust samples. These findings demonstrated that HVAC filters can serve as a noninvasive tool for SARS-CoV-2 detection in nonhealthcare settings, leveraging existing building infrastructure to support environmental monitoring.