AIRBORNE VIRUS COLLECTION USING THE BIOSAMPLER AT VARIOUS SAMPLING CONDITIONS

Abstract

For several decades, humans have faced challenges from various respiratory viruses, such as influenza viruses and coronaviruses. These viruses can spread through multiple transmission routes, including droplets, direct and indirect contact, and aerosols. Among these routes, aerosol transmission is particularly critical because airborne virus particles (or viral aerosols) can remain suspended in the air for hours, depending on their size. This allows the virus to spread and infect people through inhalation. To proactively prevent and mitigate airborne virus transmission, it is important to collect airborne viruses using an appropriate air sampler before measuring their concentrations. The purpose of this study is to characterize the widely used impinger, named the SKC BioSampler. The BioSampler has been used in many previous studies to sample various kinds of bioaerosols. Although airborne virus sampling using the BioSampler has been characterized in many studies, only a few studies investigated the effect of flow rates including its maximum sampling flow rates. Thus, the performance of the BioSampler was evaluated under a range of sampling conditions in this study: flow rates of 4.0, 8.0, 10.0, 12.5, and 13.3 standard L/min (SLPM) (4.0, 8.1, 11.3, 17.6, and 23.5 L/min at the BioSampler outlet, respectively); sampling periods of 10, 60, and 360 min; three airborne virus concentrations of MS2 bacteriophages (108, 106, and 104 PFU/m3) and two airborne virus concentrations of influenza A viruses (106, 105 gene copies/m3) at the BioSampler inlet; collection liquid volumes of 20 and 13 mL. Virus concentrations were determined through plaque assay for MS2 bacteriophages, and reverse transcription quantitative polymerase chain reaction (RT-qPCR) assay for influenza A viruses. For viable MS2 viruses, both the relative infectious virus concentration (RIVC) and the intrinsic collection efficiency (ICE) increased with sampling flow rates during 10- and 60- min sampling periods. At the lowest virus concentration—similar to field-level concentrations, viruses could be detected after 360 min of sampling. Under all sampling conditions, the performance of the BioSampler at a flow rate of 13.3 SLPM was better than that at the manufacturer-recommended flow rate of 12.5 SLPM when sampling airborne viable MS2 viruses. A similar trend was observed for influenza A viruses. Both the relative total virus concentration (RTVC), as determined by RT-qPCR, and the ICE increased with the sampling flow rate. Again, 13.3 SLPM proved to be more efficient for collecting influenza virus nucleic acids compared to 12.5 L/min. Additionally, to evaluate the change in performance during 120- min sampling, sampling was conducted with initial 13-mL collection liquid volume. Between the two collection liquid volumes of 20 mL and 13 mL, RTVC did not differ significantly, but the collection efficiencies were lower when using 13 mL compared to 20 mL. This comprehensive evaluation of the BioSampler under various conditions— including sampling flow rates, sampling periods, airborne virus types, airborne virus concentrations, and collection liquid volumes—is expected to benefit future studies on airborne virus sampling.