Waterborne transmission of protozoan parasites: a review of worldwide outbreaks - an update 2017-2022

The current study presents a comprehensive review of worldwide waterborne parasitic protozoan outbreaks reported between 2017 and 2022. Totally, 416 outbreaks were attributed to waterborne transmission of parasitic protozoa. Cryptosporidium was the etiological agent in 77.4% (322) of the outbreaks, while Giardia was reported in 17.1% (71). Toxoplasma gondii and Naegleria fowleri were the causal agent in 1.4% (6), and 1% (4) of the outbreaks, respectively. Each of Blastocystis hominis, Cyclospora cayetanensis, and Dientamoeba fragilis was mentioned in 0.72% (3) of the outbreaks. Moreover, each of Acanthamoeba spp., Entamoeba histolytica, Vittaforma corneae, and Enterocytozoon bieneusi was the causal agent in 0.24% (1) of the total outbreaks. The majority of the outbreaks (195, 47%) were reported in North America. The suspected sources for 313 (75.2%) waterborne parasitic outbreaks were recreational water and/or swimming pools, accounting for 92% of the total Cryptosporidium outbreaks. Furthermore, 25.3% of the outbreaks caused by Giardia were associated with recreational water and/or swimming pools. Developing countries are the most probable regions impacted by such outbreaks due to the lack of reliable monitoring strategies and water treatment process. There is still a need of international surveillance and reporting systems concerning both waterborne diseases and water contamination with parasitic protozoa.