Unboiled Tap Water Research Articles

Outbreak of acute gastroenteritis associated with drinking water in rural Kazakhstan: A matched case-control study.

We conducted an outbreak investigation from June 3 to 15th in a rural village in northern Kazakhstan, after surveillance showed an increase in gastroenteritis. Cases were residents who presented for medical treatment for diarrhea, fever (>37.5 °C), vomiting, or weakness from May 14 to June 15, 2021. Controls were residents matched by age ±2 years at a ratio of two controls for every case. Cases and controls were interviewed using structured questionnaires. We abstracted clinical data from medical records. We mapped cases and assessed risk for disease using conditional multivariable logistic regression. We identified 154 cases of acute gastroenteritis (attack rate of ~26 per 1,000 inhabitants). Symptoms were diarrhea, fever, vomiting, weakness, and decreased appetite. Among cases that participated (n = 107), 74% reported having drank unboiled tap water vs 18% of controls (n = 219). This was the only risk factor associated with disease (adjusted odds ratio: 18; 95% CI 9-35). Drinking water from a dispenser or carbonated drinks was protective. The city has two water supply networks; cases were clustered (107 cases in 79 households) in one. The investigation found that monitoring of quality and safety of water according to national regulations had not been conducted since 2018. No fatalities occurred, and no associated cases were reported after our investigation. Results suggest that untreated tap water was the probable source of the outbreak. The water supply had been cleaned and disinfected twice by the facility 2 days before our investigation began. Recommendations were made for regular monitoring of water supply facilities with rapid public notification when issues are detected to reduce likelihood of future drinking water associated outbreaks.

Drinking water behavior and willingness to use filters by middle-aged and elderly residents in rural areas: A cross-sectional study in Tengchong, China.

Access to safe drinking water is critical to health and development issues, and residents' drinking behavior reflects their awareness of health and water hygiene. Random sampling and face-to-face questionnaires were used to investigate the drinking water behavior, sanitation and perceptions of drinking water among middle-aged and elderly residents in Tengchong, southwest Yunnan from July 1 to July 28, 2021. Differences between groups were assessed using the Chi-square test and t-test. Two binary logistic regression analyses were conducted to explore the influencing factors of drinking unboiled tap water and willingness to use filters. Results show that 35% of residents drink unboiled tap water, and 29.8% of respondents indicated a willingness to use filters. The model results showed a strong correlation between 60 and 79 years old (OR: 0.510, 95% CI: 0.303–0.858), 80 and above years old (OR: 0.118, 95% CI: 0.038–0.365), drinking water at a regular interval (OR: 0.397, 95% CI: 0.257–0.612), wanting to gain knowledge about drinking water (OR: 0.198, 95% CI: 0.099–0.395), Perceived health risks (PHR) (OR: 0.847, 95% CI: 0.771–0.929), having kidney stones (OR: 2.975, 95% CI: 1.708–5.253) and drinking unboiled tap water (p < 0.05). 60–79 years old (OR: 0.446, 95% CI: 0.244–0.815), 80 and above years old (OR: 0.228, 95% CI: 0.064–0.812), water storage (OR: 0.088, 95% CI: 0.026–0.300), middle school and above (OR: 2.238, 95% CI: 1.289–3.883), household water treatment (HWT) (OR: 33.704, 95% CI: 9.726–116.791), Perceived health risks (PHR) (OR:1.106, 95% CI: 1.009–1.213), water authority satisfaction (WAT) (OR:0.857, 95% CI: 0.769–0.956) and willingness to use filters were correlated (p < 0.05). Our findings suggested that a certain proportion of permanent middle-aged and elderly residents in rural areas still drink unboiled tap water, and residents are less willing to use filters. Residents' perception of drinking water can reflect residents' drinking water behavior and willingness to a certain extent. It is recommended that the government and Centers for Disease Control (CDC) should strengthen relevant measures such as knowledge popularization and health education, and regulate the water use behavior of middle-aged and elderly residents. Promote safe, economical and effective household water filtration facilities to ensure public health safety.

Визначення впливу кип`ятіння на біологічні властивості водопровідної води засобами фітотестування

Introduction. Dosimetric control revealed a significant decrease in the background level of ionizing radiation from tap water after boiling it in various household appliances. As natural doses of ionizing radiation are known to be necessary for the normal functioning of living organisms, it has been suggested that the boiling process may have an adverse effect on the biological properties of water. Materials and Methods. To confirm or refute the indicated assumption, the seeds of barley (Hordeum vulgare) were germinated on tap water, which was boiled in one of the household appliances (microwave oven, electric kettle, ordinary kettle), and measured the length of the roots and epicotyls in 4-day seedlings. Based on the data obtained, the average values of the respective indicators were calculated. Quantitative data were obtained on representative sample sizes and are statistically significant with a probability of 0.05. Results and Discussion. The data obtained during the experimental study indicate that boiled water had a positive effect on the growth of roots and epicotyls of barley seedlings. And if for epicotyls the differences in comparison with the control were statistically insignificant, then for the roots in all experimental variants of germination in boiled water was found a statistically significant increase in the average length of the roots compared to unboiled water (control). Thus, the average length of roots during germination of barley seeds in water boiled on a gas stove was 40.0 ± 4.1 mm, on water boiled in an electric kettle - 33.6 ± 4.6 mm and on water, boiled in a microwave oven, - 32,4 ± 3,5 mm, against 25,7 ± 4,9 mm in control. Thus, (i) boiled tap water, which was obtained in various ways, is able to stimulate growth processes during the germination of barley seeds; (ii) this phenomenon is observed in relation to root growth after all methods of water treatment; (iii) the greatest stimulation of root growth was caused by water boiled on a gas stove. In the second series of experiments to identify the possible effect of substances dissolved in tap water on its biological properties, a comparative analysis of the growth effects of unboiled tap water and distilled tap water (which underwent deep purification) was performed. The data obtained indicate that distilled water stimulates the growth of roots of barley seedlings comparative by unboiled tap water: when germinating barley seeds in distilled water, the average length of the roots of seedlings was 16.1 ± 3.33 mm, while in germinating on unboiled tap water - 9.35 ± 0.79 mm. The next stage of the study was to determine the effect of the level of water purification by boiling on the growth parameters of phytotest. The obtained results indicate that boiling distilled water on a gas stove helped to improve its growth qualities: seedlings grown on such water had an average root length more than 2 times higher than the control values. At the same time, distilled water, which does not underwent such treatment, stimulated less, albeit reliable, seedling root growth. Therefore, the level of tap water purification determines the appropriate degree of its stimulation of root growth processes of barley seedlings. Conclusions. Studies have shown a positive effect of boiled tap water on the average length of seedling roots. The magnitude of the effect depended on the type of device in which the boiling water was carried out. Boiled distilled water also promoted seedling root growth. Possible cause for improvement of growth qualities of water was removal or destruction in the process of boiling of gases and soluble substances which are either unfavorable for the growth of the plant organism or prevent the ice-like structures formation, in the microcavities of which are circulating monomers of water are available for aquapores of living organisms. At the same time, despite the growth-promoting effect, potentially boiled tap water may have mutagenic properties that the growth phytotest does not detect.

Impact of Lead Exposure on Thyroid Status and IQ Performance among School-age Children Living Nearby a Lead-Zinc Mine in China

BackgroundLead exposure is one of the most concerning public health problems worldwide, particularly among children. Yet the impact of chronic lead exposure on the thyroid status and related intelligence quotient performance among school-age children remained elusive. ObjectiveThe aim of this study was to evaluate the influence of lead exposure on the thyroid hormones, amino acid neurotransmitters balances, and intelligence quotient (IQ) among school-age children living nearby a lead-zinc mining site. Other factors such as rice lead levels, mothers’ smoking behavior, and diet intake were also investigated. MethodsA total of 255 children aged 7-12 years old were recruited in this study. Blood lead level (BLL), thyroid hormones including free triiodothyronine (FT3), free thyroxine (FT4) and thyroid stimulating hormone (TSH), and amino acid neurotransmitters such as glutamate (Glu), glutamine (Gln), and γ-aminobutyric acid (GABA) were measured using graphite furnace atomic absorption spectroscopy (GFAAS), chemiluminescence immunoassay, high performance liquid chromatography (HPLC). Raven's standard progressive matrices (SPM) and the questionnaire were used to determine IQ and collect related influence factors. ResultsThe average BLL of children was 84.8 μg/L. The occurrence of lead intoxication (defined as the BLL ≥ 100 μg/L) was 31.8%. Serum TSH levels and IQ of lead-intoxicated children were significantly lower than those without lead toxicity. The GABA level of girls with the lead intoxication was higher than those with no lead-exposed group. Correlation analyses revealed that BLL were inversely associated with the serum TSH levels (R= -0.186, p < 0.05), but positively related with IQ grades (R = 0.147, p < 0.05). Moreover, BLL and Glu were inversely correlated with IQ. In addition, this study revealed four factors that may contribute to the incidence of lead intoxication among children, including the frequency of mother smoking (OR = 3.587, p < 0.05) and drinking un-boiled stagnant tap water (OR = 3.716, p < 0.05); eating fresh fruits and vegetables (OR = 0.323, p < 0.05) and soy products regularly (OR = 0.181, p < 0.05) may protect against lead intoxication. ConclusionLead exposure affects the serum TSH, GABA levels and IQ of school-aged children. Developing good living habits, improving environment, increasing the intake of high-quality protein and fresh vegetable and fruit may improve the condition of lead intoxication.

Development of a Cryptosporidium-arsenic multi-risk assessment model for infant formula prepared with tap water in France

Tap water is used in France to reconstitute powder infant formula, although it is not sterile and possibly contaminated by microbiological and chemical hazards. The present study aims to quantify risks of using tap water in France for the preparation of infant formula, during the first six months of life.Cryptosporidium and arsenic were selected as hazards of greatest concern in microbiology and chemistry, respectively. A probabilistic model was developed using French (when available) and European (alternatively) data. Second order Monte Carlo simulation was used to separate uncertainty and variability of inputs. Outputs were expressed at the individual level as probability of illness and at the population level, using a common metric, the DALY (Disability Adjusted Life Year). Two scenarios of milk preparation were considered: with un-boiled or boiled tap water.Consuming infant formula rehydrated with un-boiled tap water during the first six months of life led to a total of 2250 DALYs per 100,000 infants (90% uncertainty interval [960; 7650]) for Cryptosporidium due to diarrhea, and 1 DALY [0.4; 2] for arsenic due to expected lifetime risk of lung and bladder cancer as a result of early exposure in life. For the entire population, boiling water would suppress the risk from Cryptosporidium. In contrast, the incremental cancer risk was low at the population level but elevated for 5% of the population exposed to high levels of arsenic. A stringent monitoring of tap water supply points should be continued. This multi-risk assessment model could help public health authorities and managers in evaluating both microbiological and chemical safety issues associated with using infant formula prepared with tap water.

Molecular epidemiology and associated risk factors of rotavirus infection among children < 5 yrs hospitalized for acute gastroenteritis in North Eastern, Kenya, 2012.

IntroductionRotavirus is a leading cause of morbidity and mortality among children under five years worldwide. This study aimed to characterize the circulating genotypes of rotavirus and to determine risk factors of rotavirus infection in North Eastern, Kenya before the introduction of rotavirus vaccines.Methodswe conducted a cross sectional study among children < 5 years old hospitalized for acute gastroenteritis at the study hospital. Rotavirus was detected in stool specimens and further characterized using PAGE and RT-PCR. Socio-demographic and risk factor information was collected using a standard questionnaire.Resultswe enrolled 237 children into the study hospitalized with acute gastroenteritis. Of these, 41 (17%) tested positive for group A rotavirus in stool specimens. Age < 2 years, unboiled tap water, underweight and low birth weight were identified as independent risk factors of rotavirus infection. Majority 8 (57%) of the detected rotavirus RNA profiles were long electropherotypes. G3, G9 and P4 were the predominant genotypes identified.ConclusionRotavirus is an important aetiology of acute gastroenteritis among children under five years in this region. Risk factors common in other regions and rotavirus vaccine preventable genotypes are responsible for infection. We recommend the introduction of rotavirus vaccines, coupled with good infant nutrition, safe water supply and maternal hygienic practices during infant feeding.

우리나라 먹는물의 크립토스포리디움에 의한 건강위해도 평가 연구

Objectives: Cryptosporidium, a protozoan parasite, has been recognized as a frequent cause of waterborne disease due to its extremely strong resistance against chlorine disinfection. Although there has as yet been no report of a Cryptosporidium outbreak through drinking water in Korea, it is important to estimate the health risk of Cryptosporidium in water supply systems because of the various infection cases in human and domestic animals and frequent detection reports on their oocysts in water environments. Methods: This study evaluated the annual infection risk of Cryptosporidium in tap water using the quantitative microbial risk assessment technique. Exposure assessment was performed upon the results of a national survey on Cryptosporidium on the water sources of 97 large-scale water purification plants in Korea, water treatment efficacy, and daily unboiled tap water consumption. The estimates of the US Environmental Protection Agency on the mean likelihood of infection from ingesting one oocyst were applied for effect assessment. Results: Using probabilistic methods, mean annual infection risk of Cryptosporidiosis by the intake of tap water was estimated to fall within the range of <TEX>$2.3{\times}10^{-4}$</TEX> to <TEX>$1.0{\times}10^{-3}$</TEX> (median <TEX>$5.7{\times}10^{-4}$</TEX>). The risk in using river sources was predicted to be four times higher than with lake sources. With 0.5-log higher removal efficacy, the risk was estimated to be <TEX>$1.8{\times}10^{-4}$</TEX>, and could then be lowered by one-third. Conclusions: These estimations can be compared with acceptable risk and then used to determine the adequacy and priority of various drinking water quality strategies such as the establishment of new treatment technology.

Occurrence and potential health risk of Cryptosporidium and Giardia in the Three Gorges Reservoir, China

The Three Gorges Reservoir (TGR) is the biggest lake in the world and a major water source in China. There is no information about occurrence and impact of Cryptosporidium and Giardia on the aquatic ecosystem. 61 surface water samples from 23 monitoring sites and 5 treated effluent samples were collected and analyzed. Cryptosporidium oocysts and Giardia cysts were found, respectively, in 86.4% and 65.2% of a total of 66 water samples, with high concentrations in treated effluent. The mean percent recovery was 29.14% for oocysts and 34.86% for cysts. A seasonal pattern was observed, with positive samples for Cryptosporidium more frequent in flood period and positive samples for Giardia more frequent in impounding period. Counts of enterococci, fecal coliforms and total coliforms, and turbidity were significantly associated with Cryptosporidium concentration in backwater (water in a main river which is backed up by the Three Gorges Dam) areas of tributaries but not Giardia. High associations were also found between oocyst and cyst in backwater areas of tributaries and cities. The risks of infection and illness due to water consumption in four different exposure routes were estimated. The results showed that swimming in the TGR has the highest infection risk with 1.39 × 10−3 per time (95% confidence interval (CI): 0.05–600.3 × 10−5) for Cryptosporidium and 2.08 × 10−4 per time (95% CI: 0.05–878.87 × 10−6) for Giardia, while directly drinking unboiled tap water treated with the conventional process has the highest morbidity with 524.98 per 100,000 population per year (95% CI: 10.35–2040.26) for Cryptosporidium and 5.89 per 100,000 population per year (95% CI: 0.08–22.67) for Giardia. This study provides new useful information for drinking water plants, health care workers and managers to improve the safety of tap water and deduce the risk of surface water contamination in China.

Crisis Communication: An Inequalities Perspective on the 2010 Boston Water Crisis

Although the field of crisis risk communication has generated substantial research, the interaction between social determinants, communication processes, and behavioral compliance has been less well studied. With the goal of better understanding these interactions, this report examines how social determinants influenced communications and behavioral compliance during the 2010 Boston, Massachusetts, water crisis. An online survey was conducted to assess Boston residents' knowledge, beliefs, attitudes, mass and interpersonal communication, and preventive behaviors on emergency preparedness topics dealing with the water crisis. Of a total sample of 726 respondents, approximately one-third (n = 267) reported having been affected by the water crisis. Only data from affected participants were analyzed. Following an order to boil water, 87.5% of respondents refrained from drinking unboiled tap water. These behaviors and other cognitive and attitudinal factors, however, were not uniform across population subgroups. All communication and behavioral compliance variables varied across sociodemographic factors. Crisis communication, in conjunction with other public health preparedness fields, is central to reducing the negative impact of sudden hazards. Emergency scenarios such as the Boston water crisis serve as unique opportunities to understand how effectively crisis messages are conveyed to and received by different segments of the population.

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

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.

Investigating vomiting and/or bloody diarrhoea in Campylobacter jejuni infection

Campylobacter jejuni infection frequently presents as acute enteritis with diarrhoea, malaise, fever and abdominal pain. Vomiting and bloody diarrhoea are reported less frequently. To investigate potential host, micro-organism or environmental factors that might explain the different clinical presentations, the features of laboratory-confirmed Campylobacter jejuni cases presenting with vomiting and/or bloody diarrhoea were compared with cases who did not report either clinical manifestation. Single variable analysis and logistic regression were employed. Explanatory variables included food, water and environmental risks. Cases who reported vomiting and/or bloody diarrhoea tended to suffer a longer illness and were more likely to require hospital admission. Independent risks identified were being a child, female gender, consumption of poultry other than chicken, pre-packed sandwiches and sausages, and reported engineering work or problems with drinking-water supply. A dose-response relationship with vomiting and/or bloody diarrhoea and increasing daily consumption of unboiled tap water was observed also. Vomiting and/or bloody diarrhoea characterized the more severe end of the disease spectrum and might relate to host susceptibility and/or infective dose. The role of unboiled tap water as a potential source of C. jejuni infection in England and Wales requires further investigation.

Sporadic cryptosporidiosis, North Cumbria, England, 1996-2000.

Risk factors for sporadic cryptosporidiosis were determined in 152 patients and 466 unmatched controls who resided in two local government districts in North Cumbria, North West England, from March 1, 1996, to February 29, 2000. Risk was associated with the usual daily volume of cold unboiled tap water drunk (odds ratio [OR] 1.40, 95% confidence intervals [CI] 1.14 to 1.71 per pint consumed per day [p = 0.001]) and short visits to farms (OR 2.02, 95% CI 1.04 to 3.90, p = 0.04). Fifty-six (84%) of 67 fecal specimens from patients obtained from January 1, 1998, and February 29, 2000, were Cryptosporidium parvum genotype 2 (animal and human strain). Livestock fecal pollution of water sources appears to be the leading cause of human sporadic cryptosporidiosis in this population and shows the need for better protection of water catchments from livestock and improved drinking water treatment in this area of England.

CRYPTOSPORIDIOSIS

Historical public health concerns about the transmission of communicable disease through drinking water have returned to prominence since the emergence of new organisms, such as Cryptosporidium parvum, which initially eluded twentieth century water treatment procedures. Rates of cryptosporidiosis are high in New Zealand by international standards. Collation of national data on communicable disease and drinking water quality has shown that residents of small communities do not enjoy the same quality of drinking-water as their counterparts in major urban centres, and they also experience higher reported rates of cryptosporidiosis. Drinking water quality is associated with socio-economic deprivation at small area level. Aspects of our freshwater ecology, and the ubiquitous use of surface water drinking supplies, may contribute to high rates of disease. Individual level data are important to further our understanding of the relationship between people, drinking water supplies, and patterns of disease transmission in the community. Therefore, we sought to identify risk factors for exposure to cryptosporidiosis among blood donors in New Zealand, and test those donors for serological evidence of exposure to Cryptosporidium parvum. Methods Cross-sectional anonymous self-completed questionnaire survey of blood donors in two small New Zealand towns, and serological investigation of antibodies to Cryptosporidium parvum. Results Ninetynine percent of eligible donors agreed to participate. Exposure to possible risk factors was common and included drinking unboiled tap water, contact with preschool children, contact with household and farm animals, travel to other urban and rural areas within New Zealand, swimming in public pools or fresh water, and travel overseas. One fifth of respondents in community A reported high risk occupations which involved exposure to young children, farm animals, hospital inpatients, or bio-specimens. Community B had a drinking water supply with an unsatisfactory public health grading. Almost one third of respondents reported illness with diarrhoea and/or vomiting in the previous year; only 12% of these participants sought medical attention for the illness and only 7% had stool samples taken. Seroprevalence was the same in the two communities, even when controlling for different exposure to risk factors. Over 60 per cent of participants showed antibodies to either the 17-kDa (63.9%; 95%CI 58.6–69.2) or 27-kDa (64.2%; 95%CI 59–69.4) Cryptosporidium parvum antigen groups. Half the participants had antibodies to both antigen groups (49.5%; 95%CI 44–55). Conclusion Poor drinking water quality in New Zealand is associated with high rates of cryptosporidiosis, and with small area socio-economic deprivation. At an individual level New Zealanders are exposed to multiple risk factors for infection with Cryptosporidium parvum. The high rates of seropositivity suggest a degree of immunity in the adult population, which may not be shared by children who are more susceptible to symptomatic infection. Improvement of drinking water quality remains an issue of social equity with the potential to reduce disproportionate burdens of disease.

Cryptosporidium oocysts in a water supply associated with a cryptosporidiosis outbreak.

An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts’ persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the continued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.

Developments in microbiological risk assessment for drinking water.

1. SUMMARYThis paper considers the development of microbiologicalrisk assessment models for pathogenic agents in drinkingwater with particular reference to Cryptosporidium parvum,rotavirus and bovine spongiform encephalopathy (BSE).The available evidence suggests that there is potential forconsiderable variation in exposures to C. parvum oocyststhrough drinking water, during both outbreak and non-outbreak conditions. This spatial/temporal heterogeneityarises both from variation in oocyst densities in the rawwater and fluctuations in the removal efficiencies of drinkingwater treatment. In terms of risk prediction, modelling thevariation in doses ingested by individual drinking waterconsumers is not important if the dose–response curve islinear and the oocysts act independently during infection.Indeed, the total pathogen loading on the population asrepresented by the arithmetic mean exposure is sufficient forrisk prediction for C. parvum, BSE and other agents of lowinfectivity, providing the infecting particles (i.e. oocysts orBSE prions) are known to act independently. However, formore highly infectious agents, such as rotavirus, ignoring1. Summary, 1912. Introduction, 1922.1 Overview of the risk assessment approach, 1923. Pathogen exposures through drinking water, 1923.1 Pathogen exposures under non-outbreak condi-tions, 1933.1.1 Variation in micro-organism counts withinlarge volume samples, 1933.1.2 Effect of treatment on the spatial distribu-tion of micro-organisms, 1933.1.3 Implication for Cryptosporidium exposures todrinking water consumers under non-out-break conditions, 1953.2 A model for Cryptosporidium oocyst concentrationsin drinking water during an outbreak, 1964. Dose–response curves. Estimating the risk to humansfrom ingesting low pathogen doses, 1974.1 Cryptosporidium parvum, 1974.1.1 Experiments with salmonellas in mice suggestthat pathogens act independently and do notco-operate during infection, 1984.1.2 Acquired protective immunity for Cryptospo-ridium parvum, 1994.1.3 Virulence of different strains of Cryptospori-dium parvum, 1994.2 Human rotavirus, 1994.3 Bovine spongiform encephalopathy, 2004.3.1 The human oral ID

Simulating cryptosporidium exposures in drinking water during an outbreak

This paper predicts exposures to Cryptosporidium parvum oocysts through drinking water under conditions which are consistent with a waterborne outbreak. Sources of variation which contribute to the variation in oocyst exposures include the oocyst densities in the raw waters, the efficiency of oocyst removal by treatment and the daily consumption of unboiled tap water. Even under outbreak conditions the majority of consumers may not ingest any oocysts each day. Of those who are exposed, some ingest just one oocyst/d while others ingest higher doses, which in a small proportion approach the ID50 for C parvum. Ignoring this variation and using a single point average exposure predicts that a much larger proportion of the population is exposed each day but only ever to very low doses of oocysts. The impact of ignoring this variation on the predicted risks depends on the nature of the dose-response curve and, in particular, the assumptions made about the low dose extrapolation. The heterogeneity of oocyst densities in drinking water during an outbreak could contribute to the failure to detect oocysts in some waterborne outbreaks.

Simulating Cryptosporidium exposures in drinking water during an outbreak

This paper predicts exposures to Cryptosporidium parvum oocysts through drinking water under conditions which are consistent with a waterborne outbreak. Sources of variation which contribute to the variation in oocyst exposures include the oocyst densities in the raw waters, the efficiency of oocyst removal by treatment and the daily consumption of unboiled tap water. Even under outbreak conditions the majority of consumers may not ingest any oocysts each day. Of those who are exposed, some ingest just one oocyst/d while others ingest higher doses, which in a small proportion approach the ID50 for C parvum. Ignoring this variation and using a single point average exposure predicts that a much larger proportion of the population is exposed each day but only ever to very low doses of oocysts. The impact of ignoring this variation on the predicted risks depends on the nature of the dose-response curve and, in particular, the assumptions made about the low dose extrapolation. The heterogeneity of oocyst densities in drinking water during an outbreak could contribute to the failure to detect oocysts in some waterborne outbreaks.

Assessment of the risk of infection by Cryptosporidium or Giardia in drinking water from a surface water source

The significance of the presence in drinking water of the protozoan microparasites Cryptosporidium parvum and Giardia lamblia for public health may be analyzed by means of risk assessment. This requires quantitative knowledge of all the contributing factors, from the concentration of these organisms in the source water to the dose-response relation for the probability of infection or disease in a human host. The major contributing factors are: the concentration of cysts or occysts in raw water, the recovery of the detection method, the viability of recovered cysts or oocysts, the removal of organisms in the treatment process, and the daily consumption of unboiled tap water. To enable analysis of the uncertainty in the calculated risk of infection, each of these factors is treated as a stochastic variable, for which a suitable distribution is proposed. A frequency distribution for the probability of infection is then constructed with standard sampling techniques. This first evaluation of the calculation of the risk of infection due to exposure to Cryptosporidium oocysts and Giardia cysts via drinking water, shows that the uncertainty in the estimated removal efficiency of the treatment process dominates over uncertainities in other contributing factors.

Cryptosporidiosis: An Outbreak Associated with Drinking Water Despite State-of-the-Art Water Treatment

To determine the magnitude and source of an outbreak of cryptosporidiosis among persons with human immunodeficiency virus (HIV) infection and to determine whether the outbreak extended into the immunocompetent population. Matched case-control study and environmental investigation. Clark County, Nevada. Adults with HIV infection (36 case-patients with laboratory-confirmed Cryptosporidium parvum infection and 107 controls), matched by physician or clinic and by CD4+ cell count category. Potential risk factors for infection, death rates, and data on water quality. Review of surveillance and microbiology records identified 3 cases of cryptosporidiosis in 1992 (the first year that cryptosporidiosis was reportable in Nevada), 23 cases in 1993, and 78 cases in the first quarter of 1994. Of the 78 laboratory-confirmed cases in the first quarter of 1994, 61 (78.2%) were in HIV-infected adults. Of these 61 adults, 32 (52.5%) had died by 30 June 1994; at least 20 of the 32 (62.5%) had cryptosporidiosis listed on their death certificates. In the case-control study, persons who drank any unboiled tap water were four times more likely than persons who drank only bottled water to have had cryptosporidiosis (odds ratio, 4.22 [95% Cl, 1.22 to 14.65]; P = 0.02). For persons with CD4+ cell counts less than 100 cells/mm3, the association between tap water and cryptosporidiosis was even stronger (odds ratio, 13.52 [Cl, 1.78 to 102.92]; P = 0.01). Additional data indicate that this outbreak also affected persons who were not infected with HIV. No elevated turbidity values or coliform counts and no Cryptosporidium oocysts were found in testing of source (Lake Mead) or finished (treated) water during the study period, but so-called presumptive oocysts were intermittently found after the investigation in samples of source water, filter backwash, and finished water. A cryptosporidiosis outbreak was associated with municipal drinking water, despite state-of-the-art water treatment and water quality better than that required by current federal standards. This outbreak highlights the importance of surveillance for cryptosporidiosis and the need for guidelines for the prevention of water-borne-Cryptosporidium infection among HIV-infected persons.

Outbreak of cryptosporidiosis associated with a disinfected groundwater supply

In an outbreak of cryptosporidiosis in Warrington, a town in North-West England, 47 cases were recorded between November 1992 and February 1993, most within the first month. There was a strong statistical association between cases and residence in an area supplied from two groundwater sources. In a case-control study, a strong association between having drunk unboiled tap water from these sources, and a dose-response relationship were found. Oocysts were not detected in the water supply. During very heavy rainfall one source of water was found to drain surface water directly from a field containing livestock faeces, thereby bypassing natural sandstone filtration. Exceptionally heavy rainfall occurred at the probable time of infection. After withdrawal of the original water supply, the outbreak rapidly subsided. It was concluded that there was very strong evidence that this outbreak was waterborne. This, the second documented outbreak of cryptosporidiosis attributable to a groundwater supply, demonstrates that infection can be transmitted from a disinfected groundwater source despite apparently satisfactory treated water quality. We recommended that guidelines for protection of groundwater are implemented, raw groundwater should be routinely monitored for microbiological contamination, and the structure of all sources and waterworks should be assessed in risk surveys of water catchment areas.