Concentration and risk assessment of Cryptosporidium infection associated with exposure to the Njoro River, Njoro Sub-County, Nakuru, Kenya

Abstract

Background Cryptosporidium is a gastrointestinal pathogen. The oocysts are transmitted through the environment, and drinking contaminated water is one particular route. There is heavy pollution of Cryptosporidium in Njoro River, the main source of drinking water for humans and animals around the watershed. However, there is no information on the parasite concentration and estimated health risk exposed to these populations. This study determined the level of contamination and risk of infection by Cryptosporidium parasites in Njoro River. Water samples were collected monthly from three ecological sites along Njoro River for twelve months. Cryptosporidium oocysts were concentrated from these water samples using calcium carbonate flocculation method, examined and counted using epifluorescent microscopy. Quantitative microbial risk assessment was applied to estimate the health risk of Cryptosporidium infection in Njoro River using a beta-Poisson dose–response model. Results The concentration of Cryptosporidium parasites in Njoro River is 0.936 ± 0.73 oocysts/litre. However, this concentration fluctuates with ecological site of the river; highest concentration occurs at downstream (1.325 ± 0.73), followed by midstream (0.917 ± 0.74) and least at upstream (0.567 ± 0.54). Concentration of Cryptosporidium in the river is higher during wet than dry seasons, with the difference in mean concentrations between the two seasons being significant (t(34) = − 6.101, p < 0.01). There was a negative correlation between Cryptosporidium concentration, temperature and pH, while a strong positive correlation existed between Cryptosporidium concentration and turbidity. The daily probability of infection by Cryptosporidium in Njoro River watershed is 0.25, while the annual risk is 0.99. Conclusions Njoro River is heavily polluted with Cryptosporidium parasites. This exposes both the humans and animals that drink water from this river to a high risk of cryptosporidiosis, a potentially fatal infection particularly in immunocompromised individuals.