Quantitative microbial risk assessment (QMRA) of occupational exposure to SARS-CoV-2 in wastewater treatment plants.

The current global Severe Acute Respiratory Syndrome- Coronavirus-2 (SARS-CoV-2) epidemic has heightenedcalls for studies to evaluate respiratory exposure for wastewater treatment workers. In this globalfirst study,we assess occupationalhealth riskstowastewatertreatment plant(WWTP) operatorsfrom inhalation of aerosol-ized SARS-CoV-2 using a Quantitative Microbiological Risk Assessment (QMRA) framework. The following con-siderations were used to develop the QMRA and assess the illness risks to workers: a) the proportion of thepopulation who are infected and thus responsible for shedding SARS-CoV-2 into raw wastewater; b) the concen-tration of SARS-CoV-2 in raw and treated wastewater; c) the volume of aerosolized water inhaled by a WWTPoperator during work; d) humidity and temperature-dependent viability of coronaviruses in aerosolized wastewater; e) estimation of the amount, frequency, and duration of exposure; and f) exposure doses. The variableswere then fed into an exponential dose response model to estimate the risks in three scenarios representinglow-grade, moderate and aggressive outbreaks. These scenarios were designed on the assumption of 0.03%,0.3% and 3% of the wastewater-generating population being infected with SARS-CoV-2. In terms of averaged-out illness risk profiles, the individual illness risks for low grade, moderate and aggressive outbreak scenarios re-spectively are 0.036, 0.32 and 3.21 illness cases per 1000 exposed WWTP operators. Our study suggests that therisk of accidental occupational exposure to SARS-CoV-2 in raw wastewater, via inhalation at the WWTP environ-ment, is negligible, particularly when less than 0.3% of the population served by the plant are actively infected.