Sporadic Cryptosporidiosis Decline after Membrane Filtration of Public Water Supplies, England, 1996–2002

An outbreak in the autumn of 2005 resulted in 218 confirmed cases of Cryptosporidium hominis.The attack rate (relative risk 4.1, 95%CI 2.8-9.1) was significantly higher in the population supplied by Cwellyn Water Treatment Works (WTW). A case-control study demonstrated a statistically significant association (odds ratio 6.1, 95% CI 1.8 -23.8) between drinking unboiled tap water and C. hominis infection. The association remained significant in a logistic regression analysis, with an adjusted odds ratio of 1.30 (95 CI 1.05-1.61) per glass of unboiled tap water consumed per day. This evidence together with environmental and associated microbiological investigations, and the absence of effective treatment to remove Cryptosporidium oocysts at the WTW, led to the conclusion that the outbreak was waterborne. Oocyst counts in final treated water at the WTW and at different points in the distribution system were consistently very low, maximum count in continuous monitoring 0.08 oocysts per 10 litres. Data from continuous monitoring and the epidemic curve is consistent with the hypothesis that low numbers of oocysts of C hominis were present in treated water continuously during the outbreak and these were of sufficient infectivity to cause illness. All surface water derived water supplies present a potential risk to human health and appropriate control measures should be in place to minimise these risks.

Section: Resultsmentioning

confidence: 99%

A Cryptosporidium hominis outbreak in North-West Wales associated with low oocyst counts in treated drinking water

Mason¹,

Chalmers

Carnicer-Pont

et al. 2009

“…Traditionally, epidemiology is associated with the study of epidemics and localized outbreaks (two or more associated cases). Epidemiologic study methods, however, can also be used for the study of sporadic (endemic) and pseudo-sporadic (diffuse, low-level outbreaks only identified as associated by such studies and by typing of isolates, particularly if these are unusual strains) infection that may share common features with outbreaks such as potential routes of transmission, including water (Casemore 1995;Meinhardt et al 1996;Goh et al 2004Goh et al , 2005Hunter et al 2004). The outcome of the contamination of water supply and transmission to consumers depends on complex dynamics with various, usually ill characterised, factors-the organism, the exposed persons (and their levels of immunity) and the environment (Casemore 1994(Casemore , 1995Meinhardt et al 1996).…”

Section: Definitions and General Aspects Of Immunologymentioning

confidence: 99%

Towards a US national estimate of the risk of endemic waterborne disease – sero-epidemiologic studies

Casemore

2006

Worldwide literature on serological methods and sero-surveys on waterborne pathogens has been reviewed. Outbreak investigation and research reports have also been examined to aid understanding of the serological response and transmission dynamics. The aim was to seek an estimate of seroprevalence and to determine if this could inform the US national estimate of risk for endemic waterborne infection associated with public water supplies. Antibody responses indicate infection, both symptomatic and asymptomatic, so probably give a truer indication of prevalence. Outbreak data can probably be regarded as the upper bound for seroprevalence estimations. Antibody is not necessarily protective per se but is a good indicator for at least partial resistance to symptomatic infection; absence of antibody will normally imply susceptibility.Pathogens transmitted by water are commonly transmitted by other routes. However, the fact that other transmission routes are more common does not detract from the potential protective effect of immunity when waterborne transmission occurs. Data indicate that seroprevalence varies widely, reflecting geographic, social and hygiene factors, but is generally greater where surface water sources are used rather than groundwater. Areas of low seroprevalence may expect a high attack rate in the event of contamination of their water supply.Key words | Campylobacter, Cryptosporidium, ELISA, endemic infection, E. coli 0157, Giardia, molecular studies, noroviruses, outbreaks, sero-epidemiology, seroprevalence, waterborne pathogens, western blot ABBREVIATIONS DEFINITIONS AND GENERAL ASPECTS OF IMMUNOLOGYEpidemiology, at its simplest, is the study of the occurrence (number and frequency) and distribution of cases by person This paper is in the public domain: verbatim copying and redistribution of this paper are permitted in all media for any purpose, provided this notice is preserved along with the paper's original DOI. Anyone using the paper is requested to properly cite and acknowledge the source as J. The outcome of the contamination of water supply and transmission to consumers depends on complex dynamics with various, usually ill characterised, factors-the organism, the exposed persons (and their levels of immunity) and the environment (Casemore 1994(Casemore , 1995Meinhardt et al. 1996).In order to better understand the natural history of waterborne infections and the complexities of the dynamics of transmission (see Figure 1), epidemiological investigations can be enhanced by serologic studies . The purpose of this paper concerns the national estimate of risk of endemic infection from water. However, reports on immunological studies and on the investigation of outbreaks are fundamental to the understanding of endemic infection and illness. In general terms, prevalence in outbreaks likely represents the upper boundary for endemic infection estimates.Sero-epidemiology is a form of study in which the demonstration of antibodies to the organism of interest is used as a surrogate or marker for the d...

“…While some studies have found a decreased risk of endemic enteric illness to be associated with improved water treatment, this and other studies have not (Hellard et al 2001(Hellard et al , 2002McConnell et al 2001;Goh et al 2005). A study in northwest England estimated a 79% reduction in the incidence of cryptosporidiosis after the introduction of membrane filtration (Goh et al 2005).…”

Section: Discussionmentioning

confidence: 94%

“…Goh et al (2005) found that microfiltration was associated with a reduction in sporadic cases of cryptosporidiosis at a United Kingdom site. Several randomized household intervention studies have been conducted in Australia, Canada and the US (Payment et al 1991;Hellard et al 2001;Colford et al 2005).…”

Section: Introductionmentioning

confidence: 97%

Enteric illness risks before and after water treatment improvements

Frost

Tollestrup

Roberts

et al. 2009

This study evaluated whether occurrence of acute gastrointestinal illnesses declined after filtration and ozonation were added to a previously unfiltered, chlorinated high-quality surface water source in a northwest United States city. Enteric and other illnesses were recorded for two 6-month periods for control and intervention sites in the same city. During phase 1, chlorinated, unfiltered drinking water for both sites was obtained from protected watersheds.During phase 2, the intervention site received chlorinated, filtered and ozonated drinking water.The water was not altered in the control site. No overall differences were found in the risk of any of the illnesses after the new water treatment plant was completed. There was a significantly increased risk of diarrhoea and highly credible gastrointestinal illness in participants with three or more episodes of the same type of illness during phase 1.