The World Health Organization (WHO) has published a series of documents covering the relevance of a range of pathogens in water.
The background documents will inform the revision of WHO guidelines for drinking water quality and on sanitation and health. Examples of agents covered are Cyclospora, Salmonella, Toxoplasma gondii, Yersinia enterocolitica, Hepatitis A and E, Cryptosporidium, and Shigella.
Strong evidence
There is strong evidence linking transmission of non-typhoidal Salmonella with unsafe drinking water, inadequate sanitation, and poor hygiene. A number of drinking water outbreaks have been reported. Contaminated food is the most common source of infection while contaminated drinking water is a less common source.
Non-typhoidal Salmonella are transmitted primarily by the fecal-oral route with animals being the primary source. An approach that deals with the management of animal feces is necessary to control transmission.
Salmonella is frequently detected in drinking water samples, particularly in low-income settings and where insufficient treatment occurs. Disinfection processes, including chlorination, are effective for inactivating Salmonella. Storage of drinking water should be protected from fecal contamination by birds and other small animals. E. coli is a suitable indicator for the possible presence or absence of non-typhoidal Salmonella in drinking water.
There is also strong evidence for transmission of Toxoplasma gondii through unsafe drinking water and multiple outbreaks have been recorded.
Toxoplasma gondii can be transmitted via the fecal–oral route through consuming food or water contaminated with oocysts or via ingestion or consumption of tissue cysts in raw or undercooked meat from infected animals. Approaches that identify and control feline fecal contamination along the sanitation service and drinking water supply chains are needed to manage the risk.
Toxoplasma gondii is highly resistant to chemical disinfectants but is sensitive to UV light. The absence of E. coli is not a suitable indicator for the absence of Toxoplasma gondii in drinking water. However, the presence of E. coli is a suitable indicator of potential presence.
Other pathogens with strong evidence include typhoidal Salmonella, sapovirus, rotavirus, Entamoeba histolytica, adenovirus, Giardia duodenalis, Cryptosporidium, diarrhoeagenic E. coli, Vibrio cholerae, Hepatitis A and E viruses, and Shigella.
Moderate or low risk
There is moderate evidence linking transmission of Cyclospora cayetanensis with unsafe drinking-water, inadequate sanitation, and poor hygiene. Drinking water outbreaks have been documented but not on the same scale as other pathogens.
Transmission is primarily by the fecal-oral route. Food is the dominant source, but water is a possible source. Cyclospora cayetanensis causes watery diarrhea, abdominal cramping, weight loss, anorexia, myalgia, fatigue, and occasionally vomiting and fever. Infections occur worldwide but are more common in tropical areas.
Detection of Cyclospora via microscopy is complex, resource-intensive and may not differentiate between species and viable and non-viable oocysts. Molecular methods cannot determine viability of oocysts. The absence of E. coli is not a suitable indicator of the absence of Cyclospora cayetanensis in drinking water. However, its presence is a suitable indicator of potential presence of Cyclospora.
Other pathogens with moderate evidence are Yersinia enterocolitica and Burkholderia pseudomallei.
Staphylococcus aureus and Cronobacter Sakazakii are among agents considered to be of low health significance in drinking water.
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