The diarrhea dilemma: managing illness in Mexico. (Science Selections).

Although preventing a water supply from becoming polluted is critical, it may be even more critical to properly manage water along its path to the consumer, according to a study out of Mexico's Instituto Nacional de Salud Publica [EHP [10:A619-A624]. Each year, unsafe sewage disposal and fecal--oral transmission of pathogens are responsible for 3.2 million premature deaths from otherwise preventable enteric diseases, including diarrheal diseases, says the World Health Organization. However, Enrique Cifuentes and colleagues say that water quality indicators such as microbial counts may not always accurately predict health risks. Instead, housing deficiencies, hygiene-related behavior, water storage practices, and risk perceptions must also be considered to adequately manage enteric diseases.

The study focused on the community of Xochimilco, in a water reclamation area on the outskirts of Mexico City. The researchers evaluated a wide range of factors that might be linked with enteric diseases. Using self-reported data from guardians of children younger than 5 years old, the team evaluated 761 children during one wet season (November 1999-May 2000) and 732 during one dry season (June-October 2000), with 75% overlap in the children studied.

Diarrhea prevalence was 11.8% in the wet season and 10.7% in the dry season. During the dry season, children aged 1-2 years were most likely to suffer from diarrheal diseases, and children of all ages were most vulnerable when vegetables were washed only with water or with water and soap, not disinfected with chlorine; when drinking water was stored in an unprotected cistern or bucket or had a bad taste; and when children lived in crowded conditions.

They were least vulnerable during the dry season when water was available for toilet flushing; when drinking water was stored in a covered jar or protected cistern or bucket; when an inside shower was available; and when a piped water supply was available all day (which occurred in about 35% of the houses), rather than shutting down intermittently.

During the wet season, the only age distinction was that children older than 2 were less likely to suffer from diarrheal diseases, just as they were in the dry season. Children of all ages were most vulnerable when they ate food from street vendors and when drinking water had a perceptible color to it.

The researchers also found that cultural beliefs played an important role in disease incidence. Children who lived in households where the inhabitants believed that diarrhea is caused by forces such as the evil eye were more at risk than those in households that linked diarrhea with hygiene practices or contaminated food and water.

The study findings are based on households within 500 meters of five wells sampled for fecal coliform contamination, but showed no correlation between disease incidence and use of the two wells that were found to be contaminated. The neighborhoods are in an area where water reuse projects involving wastewater treatment and application as irrigation water are common and expanding, and have the potential to introduce contaminants into the water supply.

While the results of this study are consistent with similar studies conducted around the world, they are limited by a number of factors in the study design. For instance, the health, housing, and water supply data are self-reported. Data on water contamination are based on samples taken before chlorination and distribution, and do not represent the water actually consumed by the children, especially as about one-fifth to just over one-fourth (depending on the season) consumed bottled water. The researchers also assumed that the children did not drink from wells outside the study area. Despite these limitations, Cifuentes says this study provides good baseline data for assessing any future impacts of water reuse projects.