Pepper mild mottle virus as a potential indicator of occupational exposure to airborne viruses in wastewater treatment plants

Wastewater is a known carrier for human pathogenic viruses, with seasonal variations in concentrations, and wastewater treatment plant (WWTP) workers are a potentially overlooked occupational group regarding exposure to secondary aerosolized viruses. Exposure assessment of airborne pathogens is complicated by a lack of universal markers of viruses, no standardized sampling protocol, and challenges in detecting extremely low-abundant targets. In this study, we evaluate the risk of workers’ exposure to 4 pathogens, Adenovirus, Norovirus GI and GII, and Influenza A and the Pepper mild mottle virus (PMMoV) as an indicator for aerosolized viruses from wastewater, in 3 WWTPs in the Oslo region, Norway. We collected personal and stationary air samples in summer and winter and used digital droplet PCR (ddPCR) to enable the detection of low-abundant targets. Pathogenic viruses were detected in 22% of all samples, with similar detection rates in personal and stationary samples, with a maximum concentration of 762 genome copies/m3 air. PMMoV was detected in 69% of all samples, with concentrations ranging from 28 to 9703 genome copies/m3 air. The pathogens and PMMoV were most frequently detected at the grids, biological cleansing, sedimentation basins, and sludge treatment/de-watering stations, and were associated with tasks such as flushing, cleaning, and...