Diarrheal diseases in children from a water reclamation site in Mexico City

Environmental Health Perspectives, Oct, 2002 by Enrique Cifuentes, Leticia Suarez, Maritsa Solano, Rene Santos

This study was conducted to assess the risk of enteric diseases among children living in a water reclamation area in Mexico City. A geographic information system was used to define eligible wells and surrounding homesteads. Sixty-five water samples from five wells were tested for fecal coliform bacteria per 100 mL (FC/100 mL) during visits to 750 eligible households; caretakers only in those dwellings with children under 5 years old were interviewed throughout repeated cross-sectional surveys, conducted during 1999-2000. Data on diarrheal diseases were obtained from 761 children during the rainy season and 732 children during the dry season; their guardians also provided information on drinking water supply, sanitation, and socioeconomic variables. The presence of indicator organisms in groundwater samples pointed to fecal pollution; bacterial indicators, however, did not predict the health risk. The rates of diarrhea were 10.7% in the dry season and 11.8% in the rainy season. Children 1 year old showed the highest rate of diarrhea during the dry season [odds ratio (OR) = 2.1 with 95% confidence interval (CI), 0.99-4.71], particularly those from households perceiving unpleasant taste of tap water (OR, 1.7; 95% CI, 0.97-2.92) and consuming vegetables washed only with water (OR, 2.2; 95% CI, 1.10-4.39). Lower risk was observed in individuals enjoying full-day water supply (OR, 0.5; 95% CI, 0.27-0.86) and a flushing toilet (OR, 0.3; 95% CI, 0.16-0.67), as well as those storing water in covered receptacles (OR, 0.3; 95% CI, 0.15-0.80). Rainy season data suggested that children from households perceiving a color to their water had a higher rate of diarrhea than did those without such complaint (OR, 1.8; 95% CI, 0.93-3.67); recent consumption of food sold by street vendors was also a significant risk factor (OR, 1.6; 95% CI, 0.98-2.87). Groundwater is at risk of contamination, as indicated by the presence of FC/100 mL. The endemic pattern of diarrhea, however, reflects mostly inadequate housing, sanitation, and water-related practices. Health protection policy must be discussed. Key words: children's health, environmental risk, water quality indicators.

**********

Water and sanitation deficiencies represent a growing environmental health challenge in several regions around the globe. Unsafe sewage disposal and fecal-oral transmission of pathogens are responsible for otherwise preventable enteric diseases and 3.2 million premature deaths every year (1). In less developed countries, the disease burden falls heavily on the poor (2). This gap is perpetuated by the fact that environmental interventions have neglected sanitary needs and focused on the development of drinking water supplies instead (1,3). Yet the more dramatic "life-saving" oral rehydration salts therapy (an ethical imperative in primary health care) has shifted the attention from the actual role of prevention to cost-effective "solutions" (4). Exposure to fecal pollution is growing as a result of economic driving forces, overcrowded slums, and weak institutions.

The current population of the Mexico City metropolitan area (MCMA) is 18 million and is forecast to be 23.5 million by the year 2015 (5). Up to 75% of its water supply depends on groundwater reserves (6). Overextraction of water has led to soil subsidence and cracking of underground pipes, which may facilitate the mixture of drinking water supplies and sewage, as well as the downward migration of pollutants (7). Earlier investigations indicated high rates of groundwater positive microbiologic tests (8); despite growing concern, public health data are limited and official reports provide scarcely credible information (9). Additional gaps reflect the limitations of microbial indicators currently used to assess drinking water quality (10); therefore, the basis for "safety" criteria stipulated by national regulations is increasingly debatable (11,12).

A water reuse program, consisting of wastewater treatment and effluent reclamation (e.g., irrigation of fodder and green belts) is being developed in MCMA (13). A series of investigations is being conducted to assess the risk of enteric disease and provide some basis for future environmental interventions. This study addressed the following research questions: Is groundwater microbiologic pollution a health risk? What are the risk factors for enteric diseases? And which further questions should be addressed?

Methods

The boundaries of Mexico City were first framed within basic geostatistical areas, which in turn were characterized according to demographic variables, as provided by the national census tracks (5). Earlier investigations described the environmental indicators linked to enteric diseases, from which a "high-risk" communities approach was further developed (14). Our present case study was a second-step approach, resulting from an earlier investigation (14).

The research area is located in Xochimilco, on the outskirts of the city, where a water reclamation project is being developed. This project consists of a series of wastewater treatment plants, the effluents of which flow through a network of canals to be reused for agricultural irrigation, all of which contributes to the recharge of groundwater reserves, for subsequent extraction (i.e., pumping wells).