Establishing genotypic-QMRA framework for protozoan health risk assessment in urban recreational waters

Abstract

Cryptosporidium and Giardia are globally significant protozoan pathogens, frequently linked to recreational waterborne outbreaks. This study introduces a genotypic-Quantitative Microbial Risk Assessment (QMRA) framework to evaluate the occurrence, diversity, and health risks of Cryptosporidium and Giardia in urban recreational waters. A total of 104 water samples were collected from three exposure zones over two recreational seasons in 2024 and 2025. Cryptosporidium oocysts and Giardia cysts were detected in 84.6 % and 93.3 % of samples, respectively. Genotyping identified six Cryptosporidium species including C. parvum (10.6 %) and C. andersoni (14.4 %) and three Giardia assemblages, with assemblage A (12.5 %) being dominant. Risk model showed that the annual disease burden associated with recreational exposure exceeded the World Health Organization (WHO) threshold of 1.0 × 10⁻⁶ Disability-Adjusted Life Years (DALYs) per person per year. Boating and wading activities contributed the highest risks, with estimated burdens of 1.31 and 1.25 DALYs per million persons for Cryptosporidium, and 0.71 and 0.68 DALYs pppy (per person per year) for Giardia, respectively. Sensitivity analysis identified the fraction of exposed population and exposure frequency as the most influential parameters. Human fecal contamination, indicated by a moderate correlation between HF183 markers and protozoan concentrations (r = 0.34 for Giardia), was identified as the main source of contamination. This Genotypic-QMRA approach provides a novel and scalable tool for pathogen surveillance and health risk management in urban aquatic environments.