*10.4. Protozoa*

Waterborne cryptosporidiosis is common, even in developed countries because the parasite's oocysts are resistant to chlorine, which is the main chemical treatment used for disinfecting both drinking water and indoor recreational waters, including swimming pools [138]. The oocysts are common in natural waters and can be present in source waters. A SR and MA of the impacts of weather on surface waters indicated that contamination with *Cryptosporidium* and *Giardia* was 2.61 and 2.87 higher during and after heavy rainfall [139]. A SR was used to examine the risks of endemic cryptosporidiosis, and found increased risk associated with the unsafe use of water [140]. This makes the need for risk assessment necessary. Cryptosporidiosis outbreaks may well increase if there are more frequent incidents of severe weather. In many countries, surveillance involving the laboratory identification of isolates is absent or suboptimal. Without good surveillance, outbreaks will be missed, and the prevention of these not dealt with. A SR of *Toxoplasma* outbreaks showed longer incubation following exposure to contaminated water compared to meat related exposures [141]. A SR of intestinal protozoal infections found significantly lower odds of infection in people with treated water [142]. *Giardia* transmission is not as well understood as *Cryptosporidium*, mostly because typing approaches have been suboptimal and routine surveillance in developed countries has focussed on the link to travel, rather than indigenous sources of infection [143]. Hygiene linked to water is important and occurrence in developing countries shows no relationship to rainfall [144]. However, the infection is common, and determining any change due to climate may be difficult. Both *Giardia* and *Cryptosporidium* are common in developing countries, and include a variety of species and types, and it has been suggested that climate change will increase malnutrition and contamination of water sources [145].

*Naegleria fowleri* infections are commonly associated with thermally polluted waters and cases might increase with raised temperatures. However, many of the reported infections are associated with geothermal waters that will not be greatly impacted by climate change.
