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

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. • Genotyping–QMRA pipeline linking molecular types to scenario-specific risk • Activity-resolved intake modeling for boating, wading and swimming • Annual DALYs exceed WHO threshold; boating and wading drive highest risk