Recent epidemiological studies to test microbiological quality guidelines for wastewater use in agriculture and aquaculture.

Background: New guidelines for wastewater reuse (WHO 1989) are controversial. Epidemiological studies are needed to test their validity. Cross-sectional studies of the impact of excreta use in aquaculture in Indonesia, and of wastewater use in irrigation in Mexico have been carried out.

Methods: Each study involved an exposed group using wastewater/excreta with no treatment, a control group with no wastes use, and an intermediate group, where wastewater/excreta was used but some health protection measure existed. In Mexico, the intermediate group used wastewater from a storage reservoir which met the new WHO guideline for restricted irrigation. In Indonesia, the intermediate group did not have domestic exposure to pondwater, whose quality was around forty times higher than the tentative WHO bacterial guideline for fishpond water.

Results: In Indonesia, the prevalence of diarrhoeal disease was low in adults, and unrelated to exposure, but high in children under 5 years. Multiple logistic regression analysis gave odds ratios of 1.4 (p = .06) for consumer exposure, 1.9 (p = .01) for recreational or occupational exposure and 1.6 (p = .01) for domestic exposure, when allowance was made for all other exposures and several confounding factors. In Mexico, preliminary analysis of the wet season data suggests that the increased risks of Ascaris infection and diarrhoeal disease from the use of raw wastewater are removed when water of WHO guideline quality from storage reservoirs is used.

Conclusion: WHO (1989) guidelines can be tested using cross-sectional epidemiological studies which indicate that guidelines for restricted irrigation and for aquaculture may be around the right level.