Protective masks reduced gastrointestinal risks of antibiotic-resistant E. coli for hospital wastewater treatment plant workers: A quantitative microbial risk assessment

Antibiotic-resistant bacteria (ARB) in hospital wastewater present significant but under-researched risks for wastewater treatment plant (WWTP) workers. This study evaluated annual infection risks (P_y) from exposure to ESBL-producing Escherichia coli (ESBL E. coli) and the effectiveness of protective masks. Wastewater samples from 25 hospitals in Thailand revealed 88 % of untreated samples were positive for ESBL E. coli (6.25 × 10² to 1.83 × 10⁷ CFU/100 mL, mean 2.22 × 10⁶), while 40 % of treated samples tested positive (1.00 × 10² to 1.97 × 10⁵ CFU/100 mL, mean 2.45 × 10⁴). Using quantitative microbial risk assessment and data from 917 workers, risks were calculated under three scenarios: non-resistant, antibiotic-resistant, and highly virulent E. coli. Ingestion of aerosols and droplets posed a higher infection risk than hand-to-mouth contact, with P_y often exceeding the U.S. EPA benchmark of 10^-4 per person per year. Mask use, particularly surgical and FFP2 masks, significantly reduced risks, bringing treated wastewater exposure below the benchmark. However, highly virulent E. coli risks remained high across all mask types. These findings highlight the need for effective protective measures and disinfection strategies to safeguard WWTP workers and mitigate ARB dissemination, protecting public health and environmental safety.