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OBJECTIVES: This study identified possible dose-response relationships among bathers exposed to marine waters contaminated with domestic sewage and subsequent risk of nonenteric illness. METHODS: Four intervention follow-up studies were conducted within the United Kingdom. Healthy volunteers (n = 1273) were randomized into bather and nonbather groups. Intensive water-quality monitoring was used to assign five bacteriological indices of water quality to individual bathers. Illnesses studied were acute febrile respiratory illness, and eye, ear, and skin ailments. RESULTS: Fecal streptococci exposure was predictive of acute febrile respiratory illness, while fecal coliform exposure was predictive of ear ailments. Estimated thresholds of effect occurred at bather exposures above 60 fecal streptococci and 100 fecal coliform per 100 ml of water, respectively. Although no relationship was found between eye ailments and indicator organism exposure, compared with nonbathers, bathers were at higher risk for eye ailments. CONCLUSIONS: Nonenteric illness can be transmitted via recreational contact with marine waters contaminated with sewage. These results argue against the use of a single indicator to establish water quality standards.

All previously published epidemiological studies of the health effects of bathing in marine waters contaminated with domestic sewage contain three major methodological weaknesses in study design: (1) failure to control for the substantial amount of temporal and spatial variation in indicator organism densities shown to occur within just a few hours at marine water bathing locations; (2) failure to relate indicator organism density directly to the individual bather; and (3) failure to rigorously control for non-water-related risk factors on previously reported associations between bathing in marine waters and illness among such bathers. We report the results of two intervention follow-up studies specifically designed to address these methodological weaknesses. We restricted study outcome to bathing-associated gastroenteritis since this is the illness most consistently reported to be associated with bathing in marine waters, and upon which both current US Marine Water Quality Criteria and other standards used worldwide are based. Our results show that faecal streptococci was the only indicator organism to predict the occurrence of gastroenteritis among bathers, and this occurred at only one of the three water quality sampling depths used in our study. The consumption of three different foods known or suspected to act as vectors in the transmission of gastroenteritis, as well as one non-food, non-water-related risk factor for gastroenteritis were found to significantly increase the risk of gastroenteritis among bathers. Multiple logistic regression modelling showed that these non-water-related risk factors confounded the relationship between exposure to marine waters of varying faecal streptococci densities and the occurrence of gastroenteritis among bathers to a moderate degree. Moreover, these analyses showed that the risk of gastroenteritis to the individual bather caused by these non-water-related risk factors, approximated the risk of gastroenteritis among bathers exposed to waters containing relatively high faecal streptococci densities. The implications of these findings with regard to the validity of present marine water quality criteria and on the need for, and design of, future epidemiological studies of bathing water associated illness are discussed.

Intestinal pathogens and parasites are a problem associated with the disposal of sewage sludge to pasture. Those of major importance are ova of the beef tapeworm (Taenia saginata) and Salmonella bacteria. Techniques for routine monitoring of pathogens and intestinal parasite levels in sludge together with design of simple methods for their removal have intensified, because disposal of sewage sludge to pasture is coming under increasing international surveillance. The performance during field trials of a proprietary peracetic acid compound (containing 36 to 40% w/w peracetic acid), hereafter referred to as PAA (100%), is described. These trials under operational conditions showed it to be a suitable bacterial and ovicidal agent for the disinfection of raw, digested and activated sludges. Concentrations ranging from 250 to 1000 mg PAA/l have achieved up to 99% inhibition of hatching and up to 100% destruction in viability of tapeworm embryos suspended in raw and digested sludges. Similarly these concentrations resulted in 5 log reductions in salmonellae seeded in raw sludge. A dose of 250 mg PAA/1 reduced salmonellae levels from 4600 organism/100cm3 to <30/100cm3 during gravity thickening of surplus activated sludge. Results from 46 tanker loads of consolidated surplus activated sludge revealed that salmonellae levels were reduced from 2400 organisms/100 cm3 to <30/100 cm3 at doses of 500, 400 and 300 mg PAA/1. At a lower dose of 150 mg PAA/1 levels were reduced to within a range of <30 to 430 organisms/100 cm3. At optimum disinfection concentrations for the destruction of both bacteria and parasites, PAA was rapidly utilised resulting in safe, readily biodegradable, non-toxic residuals. The technical and practical benefits, principals of disinfecting sludge and ecological safeguards are highlighted in this paper. Use is made of case histories to describe practical operating techniques.

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