Contaminated small drinking water supplies and risk of infectious intestinal disease: a prospective cohort study.

BACKGROUND: This study sought to identify whether elevated risk of infectious intestinal disease (IID) exists in contaminated small water supply consumers compared with consumers drinking from small supplies complying with current standards and whether this effect is modified by age. METHODOLOGY AND PRINCIPAL FINDINGS: A prospective cohort study of 611 individuals receiving small supplies in England was conducted. Water supplies received sanitary inspection and examination for indicator bacteria and participants maintained a daily record of IID. Regression modeling with generalized estimating equations that included interaction terms between age and indicators of fecal pollution was performed. Crude IID prevalence was 9 · 3 days with symptoms/1000 person days (95%CI: 8 · 4, 10 · 1) and incidence was 3 · 2 episodes/1000 person days (95%CI, 2 · 7, 3 · 7) or 1 · 2 episodes per person year. Although there was no overall association between IID risk and indicator presence, there was strong interaction between age and indicator presence. In children under ten, relative risk (RR) of IID in those drinking from enterococci contaminated supplies was 4.8 (95%CI: 1.5, 15.3) for incidence and 8.9 (95%CI: 2.8, 27.5) for prevalence. In those aged 10 to 59, IID risk was lower but not statistically significant. CONCLUSIONS: Contaminated small water supplies pose a substantial risk of IID to young children who live in homes reliant on these supplies. By contrast older children and adults do not appear to be at increased risk. Health care professionals with responsibility for children living in homes provided by very small water supplies should make parents aware of the risk.

Quantitative microbial risk assessment of cryptosporidiosis and giardiasis from very small private water supplies.

This article reports a quantitative microbial risk assessment of the risk of Giardia and Cryptosporidium in very small private water supplies. Both pathogens have been implicated in causing outbreaks of waterborne disease associated with such supplies, though the risk of endemic disease is not known. For exposure assessments, we used existing data to derive regression equations describing the relationships between the concentration of these pathogens and Escherichia coli in private water supplies. Pathogen concentrations were then estimated using national surveillance data of E. coli in private water supplies in England and France. The estimated risk of infection was very high with the median annual risk being of the order of 25-28% for Cryptosporidium and 0.4% to 0.7% for Giardia, though, in the poorer quality supplies the risk could be much higher. These risks are substantially greater than for public water supplies and well above the risk considered tolerable. The observation that observed infection rates are generally much lower may indicate increased immunity in people regularly consuming water from private supplies. However, this increased immunity is presumed to derive from increased disease risk in young children, the group most at risk from severe disease.

Fault tree analysis of the causes of waterborne outbreaks.

Prevention and containment of outbreaks requires examination of the contribution and interrelation of outbreak causative events. An outbreak fault tree was developed and applied to 61 enteric outbreaks related to public drinking water supplies in the EU. A mean of 3.25 causative events per outbreak were identified; each event was assigned a score based on percentage contribution per outbreak. Source and treatment system causative events often occurred concurrently (in 34 outbreaks). Distribution system causative events occurred less frequently (19 outbreaks) but were often solitary events contributing heavily towards the outbreak (a mean % score of 87.42). Livestock and rainfall in the catchment with no/inadequate filtration of water sources contributed concurrently to 11 of 31 Cryptosporidium outbreaks. Of the 23 protozoan outbreaks experiencing at least one treatment causative event, 90% of these events were filtration deficiencies; by contrast, for bacterial, viral, gastroenteritis and mixed pathogen outbreaks, 75% of treatment events were disinfection deficiencies. Roughly equal numbers of groundwater and surface water outbreaks experienced at least one treatment causative event (18 and 17 outbreaks, respectively). Retrospective analysis of multiple outbreaks of enteric disease can be used to inform outbreak investigations, facilitate corrective measures, and further develop multi-barrier approaches.

Surveillance of waterborne disease in European member states: a qualitative study.

We sought to explore perceived strengths and weaknesses of surveillance systems for the detection of drinking-water-related illness in Europe based on the experience of individuals utilising such systems. We designed and conducted a qualitative semi-structured interview study with thematic analysis. Interviews took place in six European countries with seven experts in epidemiology, water and public health. Interviewees remarked upon variation between and within countries in laboratory and sampling protocols and reporting practice; these were felt to influence timeliness and sensitivity of laboratory- and clinician-report-based surveillance. Electronic reporting, reminders to report and direct report relay to national level were considered strengths of report-based surveillance. A need was expressed for more detailed case demographic information to facilitate outbreak detection. Existing infrastructure permitting, prescriptions data, anti-diarrhoeal pharmaceutical sales, absenteeism and consultations were cited as useful outbreak indicators. Information regarding consumer water quality complaints was highlighted as a potentially useful data source. Collaboration with water companies (concerning water distribution and incidents), and constructing and maintaining relationships with local and external data providers were cited as requisites of effective surveillance. Inter- and intra-organisational collaboration and information integration are likely to improve surveillance, leading to more astute estimates of the waterborne disease burden.