Academic journal article Bulletin of the World Health Organization

Bacterial Indicators of Risk of Diarrhoeal Disease from Drinking-Water in the Philippines

Academic journal article Bulletin of the World Health Organization

Bacterial Indicators of Risk of Diarrhoeal Disease from Drinking-Water in the Philippines

Article excerpt

Introduction

Seriously polluted water supplies are used by at least 1500 million people worldwide [16]. Because of the magnitude of the health problems associated with water of inadequate quality and quantity, substantial efforts have focused on how to evaluate and maximize the health benefits derived from improved water supplies. In many developing countries the high incidence of waterborne disease and widespread use of untreated and often highly polluted water sources make the accurate assessment of faecal contamination of water particularly important.

The indicator bacteria commonly used to evaluate water quality in temperate climates may not be appropriate for the tropics, where water sources are typically warm (21-31 [degrees]C) and have high nutrient levels. These characteristics influence the survival and extra-enteral regrowth of indicator bacteria and encourage the growth of non-faecal, thermotolerant indigenous microorganisms. The latter can cause heavy background growth or give false positive reactions and thereby interfere with enumeration of the indicator bacteria.

Several investigators have reported difficulties in using total and faecal coliforms to measure the sanitary quality of tropical waters, including the ability of the bacteria to multiply, to survive for long periods, and to occur in high numbers in the absence of any identifiable source of faecal pollution [21].

Current WHO bacteriological guidelines [38] for drinking-water recommend zero faecal coliforms per 100 ml of water. However, some investigators hold that this is not feasible for untreated, unpiped water sources used in developing countries [16, 39]. There is therefore a need for epidemiological-microbiological studies in tropical developing countries to define measures of water quality that accurately reflect the potential for disease transmission and to formulate realistic water guidelines applicable to the special problems and needs of such countries [14, 21, 39].

Previous epidemiological field studies that attempted to relate water supply and diarrhoeal disease have been reviewed by McJunkin [28]. Blum & Feachem [5], and Esrey et al. [13], inter alia. In an analysis of data pooled from nine separate studies, Esrey et al. concluded that improvements in water quality alone caused a median reduction of 16% in diarrhoea morbidity (range, 0-90%) and that improvements in both water quality and availability resulted in a median reduction of 37% (range, 0-82%) [13]. Among the common methodological problems observed by McJunkin [28] was the inadequate measurement of water quality. Most of 32 field studies of water supply and diarrhoeal disease he reviewed appeared not to have measured bacteriological water quality; instead, exposure to "good" or "poor" water quality was estimated by the type of water source or level of service. Only 10 of the studies reported the bacteriological quality of the water; and of these, seven measured total coliforms [29-32, 34, 35, 37], one measured faecal coliforms [22], and two measured faecal coliforms and faecal streptococci [3, 15, 33].

The present study used an epidemiological approach to evaluate four bacterial indicators of tropical drinking-water quality (faecal coliforms, Escherichia coli, enterococci, and faecal streptococci) by examining the relationship between the concentrations of these bacteria in drinking-water and the prevalence of diarrhoea in a population that consumed this water. Faecal coliforms and faecal streptococci were selected as standard indicator bacteria, while E. coli and enterococci were chosen because of their successful use in other studies, because of evidence that they are relatively faecal-specific, and because of new selective methods for their enumeration [8, 39].

Methods

General description of the study

A one-year study of the above-mentioned indicators of tropical drinking-water quality was carried out as part of two larger investigations on infant feeding practices and on the effect of water and sanitation on infant health in metropolitan Cebu, Philippines. …

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