Regional differences in presence of Shiga toxin-producing Escherichia coli virulence-associated genes in the environment in the North West and East Anglian regions of England.

Shiga toxin-producing Escherichia coli is carried in the intestine of ruminant animals, and outbreaks have occurred after contact with ruminant animals or their environment. The presence of STEC virulence genes in the environment was investigated along recreational walking paths in the North West and East Anglia regions of England. In all, 720 boot sock samples from walkers' shoes were collected between April 2013 and July 2014. Multiplex PCR was used to detect E. coli based on the amplification of the uidA gene and investigate STEC-associated virulence genes eaeA, stx1 and stx2. The eaeA virulence gene was detected in 45·5% of the samples, where stx1 and/or stx2 was detected in 12·4% of samples. There was a difference between the two regions sampled, with the North West exhibiting a higher proportion of positive boot socks for stx compared to East Anglia. In univariate analysis, ground conditions, river flow and temperature were associated with positive boot socks. The detection of stx genes in the soil samples suggests that STEC is present in the English countryside and individuals may be at risk for infection after outdoor activities even if there is no direct contact with animals. SIGNIFICANCE AND IMPACT OF THE STUDY: Several outbreaks within the UK have highlighted the danger of contracting Shiga toxin-producing Escherichia coli from contact with areas recently vacated by livestock. This is more likely to occur for STEC infections compared to other zoonotic bacteria given the low infectious dose required. While studies have determined the prevalence of STEC within farms and petting zoos, determining the risk to individuals enjoying recreational outdoor activities that occur near where livestock may be present is less researched. This study describes the prevalence with which stx genes, indicative of STEC bacteria, were found in the environment in the English countryside.

An agent-based model about the effects of fake news on a norovirus outbreak.

BACKGROUND: Concern about health misinformation is longstanding, especially on the Internet. METHODS: Using agent-based models, we considered the effects of such misinformation on a norovirus outbreak, and some methods for countering the possible impacts of "good" and "bad" health advice. The work explicitly models spread of physical disease and information (both online and offline) as two separate but interacting processes. The models have multiple stochastic elements; repeat model runs were made to identify parameter values that most consistently produced the desired target baseline scenario. Next, parameters were found that most consistently led to a scenario when outbreak severity was clearly made worse by circulating poor quality disease prevention advice. Strategies to counter "fake" health news were tested. RESULTS: Reducing bad advice to 30% of total information or making at least 30% of people fully resistant to believing in and sharing bad health advice were effective thresholds to counteract the negative impacts of bad advice during a norovirus outbreak. CONCLUSION: How feasible it is to achieve these targets within communication networks (online and offline) should be explored.

Serological responses to Cryptosporidium antigens in inhabitants of Hungary using conventionally filtered surface water and riverbank filtered drinking water.

In this study the putative protective seroprevalence (PPS) of IgG antibodies to the 27-kDa and 15/17-kDa Cryptosporidium antigens in sera of healthy participants who were and were not exposed to Cryptosporidium oocysts via surface water-derived drinking water was compared. The participants completed a questionnaire regarding risk factors that have been shown to be associated with infection. The PPS was significantly greater (49-61%) in settlements where the drinking water originated from surface water, than in the control city where riverbank filtration was used (21% and 23%). Logistic regression analysis on the risk factors showed an association between bathing/swimming in outdoor pools and antibody responses to the 15/17-kDa antigen complex. Hence the elevated responses were most likely due to the use of contaminated water. Results indicate that waterborne Cryptosporidium infections occur more frequently than reported but may derive from multiple sources.

Longitudinal surveillance of bacteraemia in haematology and oncology patients at a UK cancer centre and the impact of ciprofloxacin use on antimicrobial resistance.

OBJECTIVES: To assess and compare the current trends in bacteraemia and antimicrobial resistance and analyse the impact of ciprofloxacin prescribing on Gram-negative bacterial resistance in haematology and oncology patients. METHODS: Information on bacteraemia episodes, causative pathogens, antimicrobial resistance and consumption was compared between haematology and oncology patients at a UK cancer centre in a 14 year longitudinal surveillance study. RESULTS: Haematology patients had a 3-fold higher incidence of bacteraemia compared with oncology patients (10.9/1000 versus 3.6/1000 admissions, respectively). Coagulase-negative staphylococci were the most common Gram-positive cause of bacteraemia for both cancer groups, whereas the overall rate of methicillin-resistant Staphylococcus aureus bacteraemia was low (0.16/1000 admissions). Escherichia coli was the most common Gram-negative cause of bacteraemia for both groups, but with a higher incidence in haematology patients (0.92/1000 admissions) compared with oncology patients (0.5/1000 admissions). Pseudomonas spp. formed the second most common Gram-negative infection in haematology patients, with a 4-fold higher bacteraemia incidence compared with oncology patients (0.76 versus 0.16/1000 admissions). Ciprofloxacin resistance of Gram-negative isolates was 22% in haematology and 5% in oncology patients. The rate of ciprofloxacin use measured showed high ciprofloxacin consumption in haematology patients compared with oncology patients (3.6 versus 1.5 defined daily doses/10 admissions, respectively), suggesting that ciprofloxacin may drive resistance. CONCLUSIONS: Our longitudinal surveillance highlights the continued importance of Gram-negative bacteraemia, in particular that due to Pseudomonas, in the cancer population and raises concerns regarding increasing ciprofloxacin use and resistance.

School-based sex education is associated with reduced risky sexual behaviour and sexually transmitted infections in young adults.

OBJECTIVE: To quantify the effectiveness of school-based sexual education on risky sexual behaviour and sexually transmitted infection (STI) acquisition in adulthood. STUDY DESIGN: Online survey of sexual attitudes and behaviours. METHODS: Students at a British university were surveyed regarding where they learnt most about sex at 14 years of age, how easy they found talking about sexual issues with their parents and age at first intercourse. The effects of these factors were modelled on risk of recent unprotected intercourse and self-reported STIs in adulthood. RESULTS: Seventy-eight of 711 (11%) students reported unprotected intercourse in the 4 weeks before the survey, and 44 (6.2%) students had ever been diagnosed with an STI. Both age at first intercourse (risk reduced by 11% per year of delayed intercourse, 95% confidence interval (CI) 3-19%) and learning about sex from lessons at school (66% reduction in risk compared with learning from one's mother, 95% CI 5-88%) were associated with reductions in risk of unprotected intercourse. Factors associated with fewer STIs were age at first intercourse (17% reduction per year of delayed intercourse, 95% CI 5-28%); and learning about sex from lessons at school (85% reduction, 95% CI 32-97%), from friends of the same age (54% reduction, CI 7-77%) and from first boy/girlfriend (85% reduction, 95% CI 35-97%) compared with learning from one's mother. CONCLUSION: School-based sexual education is effective at reducing the risk of unprotected intercourse and STIs in early adulthood. Influence from friends in adolescence may also have a positive effect on the risk of STIs in later life.

Foreign travel, casual sex, and sexually transmitted infections: systematic review and meta-analysis.

OBJECTIVES: With increasing international travel it is important to understand how frequent casual travel sex and unprotected intercourse are, and what impact this may have on the risk of acquiring sexually transmitted infections (STIs). METHODS: We conducted a systematic review, and where appropriate meta-analyses, to ascertain the influence of foreign travel on behavior, including new partnerships, unprotected intercourse, and STI acquisition. RESULTS: The pooled prevalence of travel-associated casual sex was 20.4% (95% confidence interval (CI) 14.8-26.7%), with 49.4% (95% CI 38.4-60.5%) of these having unprotected intercourse. The predominant characteristics of people who had new sexual partners abroad were: young age, male gender, single status, and traveling alone or with friends, with a previous history of multiple sexual partners or an STI. People who travel or stay abroad for longer periods and men who have sex with men are at higher risk of developing new sexual partnerships and having unprotected intercourse. The risk of developing an STI is increased up to 3-fold in people who experience casual travel sex. CONCLUSIONS: New sexual partnerships and unprotected intercourse abroad are relatively common. People who develop new sexual partnerships and have unprotected intercourse abroad have an increase risk of STIs. There is, however, a paucity of information related to strategies to prevent the risk of STI acquisition during foreign travel.

Foreign travel associated with increased sexual risk-taking, alcohol and drug use among UK university students: a cohort study.

We conducted a prospective cohort study to assess sexual behaviour of students at a British University during the summer break, to explore the role of foreign travel as a risk factor of sexually transmitted infections acquisition and to determine characteristics associated with casual sex. We found that those who travelled abroad were more likely to use alcohol (RR 1.59, 95% CI 1.17-2.16) and cannabis (RR 1.35, 95% CI 1.13-1.62) and to have casual sex during holidays. They also reported more sexual relationships after holidays (RR 1.26, 95% CI 1.09-1.53). New partnerships during holidays were associated with being single, foreign travel, drinking alcohol and having previously had large number of sexual partners. The adjusted relative risk of developing new sexual partnerships with foreign travel was 2.70 (95% CI 1.11-6.61). People who travel abroad during holidays are more likely to engage in risk taking behaviour and have casual sex. They are also more sexually active after holidays.

Effect of water hardness on cardiovascular mortality: an ecological time series approach.

BACKGROUND: Numerous studies have suggested an inverse relationship between drinking water hardness and cardiovascular disease. However, the weight of evidence is insufficient for the WHO to implement a health-based guideline for water hardness. This study followed WHO recommendations to assess the feasibility of using ecological time series data from areas exposed to step changes in water hardness to investigate this issue. METHOD: Monthly time series of cardiovascular mortality data, subdivided by age and sex, were systematically collected from areas reported to have undergone step changes in water hardness, calcium and magnesium in England and Wales between 1981 and 2005. Time series methods were used to investigate the effect of water hardness changes on mortality. RESULTS: No evidence was found of an association between step changes in drinking water hardness or drinking water calcium and cardiovascular mortality. The lack of areas with large populations and a reasonable change in magnesium levels precludes a definitive conclusion about the impact of this cation. We use our results on the variability of the series to consider the data requirements (size of population, time of water hardness change) for such a study to have sufficient power. Only data from areas with large populations (>500,000) are likely to be able to detect a change of the size suggested by previous studies (rate ratio of 1.06). CONCLUSION: Ecological time series studies of populations exposed to changes in drinking water hardness may not be able to provide conclusive evidence on the links between water hardness and cardiovascular mortality unless very large populations are studied. Investigations of individuals may be more informative.

Sexual behaviour, drugs and alcohol use of international students at a British university: a cross-sectional survey.

The aim of the study was to determine whether international students have greater risk-taking behaviours that could lead to importing novel and resistant strains of sexually transmitted infections (STIs). We conducted a cross-sectional web-based survey of university students' sexual behaviour, alcohol and drug use, and self-reported diagnosis of STIs and compared these between British and international students. In all, 827 students completed the survey, of whom 123 (15%) were international students. International students were less likely to have ever drunk alcohol (95.4% versus 87.8%, P = 0.002) and used drugs (56.4% versus 41.5%, P = 0.002). International students were on average almost two years older at first intercourse (18.7 versus 17 years; P < 0.001). There were no differences in the number of sexual partners between national and international students. On a discriminant analysis model, international students were characterized by being older and from a non-white background, less likely to use cocaine, they drank alcohol less frequently and were more likely to have had unprotected intercourse with two or more partners in the previous year. In conclusion, international students tend to drink more moderately and use fewer recreational drugs than British students. However, they exhibit higher sexual risk behaviours that could lead to importing novel and resistant strains of STIs.

Sex, drugs and sexually transmitted infections in British university students.

Understanding predisposing factors for sexually transmitted infections (STIs) in young adults may identify targets for public health interventions. We conducted a cross-sectional web-based survey of university students' sexual attitudes, behaviours and lifestyles and self-reported rates of STI. A total of 827 students responded, 22.4% had two or more sexual partners in the previous year with inconsistent condom use and the lifetime prevalence of STIs was 9.6%. Factors associated with a diagnosis of STI were increasing age and number of sexual partners ever, female gender (adjusted odds ratio [AOR] 2.70, 95% confidence interval [CI] 1.31, 5.56) and use of crack (AOR 10.45, 95% CI 1.46, 75.16). For female students, these were increasing age and number of partners ever, whereas for male students having sex with other men (bisexual AOR 4.8, 95% CI 1.02, 22.595, homosexual AOR 17.66, 95% CI 3.03, 103.04) and use of crack (AOR 32.24, 95% CI 3.33, 312.08). Multiple partners and recreational drug use may predict incidence of STI. Prevention strategies need to aim at reducing risk behaviour across various activities.

Detection of Mycobacterium avium subspecies paratuberculosis from patients with Crohn's disease using nucleic acid-based techniques: a systematic review and meta-analysis.

This study is a systematic review and meta-analysis of studies using nucleic acid-based techniques to detect Mycobacterium avium paratuberculosis (MAP) in patients with Crohn's disease (CD) compared with controls. Database searches were conducted and risk difference estimates were calculated using meta-analysis. Fifty-eight studies were reviewed, 47 of which were included in the analysis. The pooled estimate of risk difference from all studies was 0.23 (95% confidence interval [CI], 0.14-0.32) using a random effects model. Similarly, MAP was detected more frequently from patients with CD compared with those with ulcerative colitis (risk difference 0.19, 95% CI, 0.10-0.28). Year of study, assay type, and inclusion of children explained some but not all of the observed heterogeneity. The data confirms the observation that MAP is detected more frequently among CD patients compared with controls. However, the pathogenic role of this bacterium in the gut remains uncertain. Our analysis demonstrates that there is an association between MAP and CD, across many sites, by many investigators, and controlling for a number of factors; however, this association remains controversial and inconclusive. Future studies should determine whether there is a pathogenic role.

Estimation of the consumption of cold tap water for microbiological risk assessment: an overview of studies and statistical analysis of data.

The volume of cold tap water consumed is an essential element in quantitative microbial risk assessment. This paper presents a review of tap water consumption studies. Study designs were evaluated and statistical distributions were fitted to water consumption data from The Netherlands, Great Britain, Germany and Australia. We conclude that the diary is to be preferred for collecting water consumption data. If a diary is not feasible, a 24 h recall would be the best alternative, preferably repeated at least once. From the studies evaluated, the mean daily consumption varies from 0.10 L to 1.55 L. No conclusions could be drawn regarding the effects of season, age and gender on tap water consumption. Physical activity, yearly income and perceived health status were reported to influence water consumption. Comparison of the different statistical probability distribution functions of the datasets demonstrated that the Poisson distribution performed better than the lognormal distribution as suggested by Roseberry and Burmaster. For quantitative microbiological risk assessment (QMRA) it is recommended to use country-specific consumption data and statistical distributions, if available. If no country specific data are available we recommend to use the Australian distribution data from the Melbourne diary study (Poisson, lambda=3.49 glasses/d) as a conservative estimate.

A systematic review of the clinical, public health and cost-effectiveness of rapid diagnostic tests for the detection and identification of bacterial intestinal pathogens in faeces and food.

OBJECTIVES: To determine the diagnostic accuracy of tests for the rapid diagnosis of bacterial food poisoning in clinical and public health practice and to estimate the cost-effectiveness of these assays in a hypothetical population in order to inform policy on the use of these tests. DATA SOURCES: Studies evaluating diagnostic accuracy of rapid tests were retrieved using electronic databases and handsearching reference lists and key journals. Hospital laboratories and test manufacturers were contacted for cost data, and clinicians involved in the care of patients with food poisoning were invited to discuss the conclusions of this review using the nominal group technique. REVIEW METHODS: A systematic review of the current medical literature on assays used for the rapid diagnosis of bacterial food poisoning was carried out. Specific organisms under review were Salmonella, Campylobacter, Escherichia coli O157, Staphylococcus aureus, Clostridium perfringens and Bacillus cereus. Data extraction was undertaken using standardised data extraction forms. Where a sufficient number of studies evaluating comparable tests were identified, meta-analysis was performed. A decision analytic model was developed, using effectiveness data from the review and cost data from hospitals and manufacturers, which contributed to an assessment of the cost-effectiveness of rapid tests in a hypothetical UK population. Finally, diagnostic accuracy and cost-effectiveness results were presented to a focus group of GPs, microbiologists and consultants in communicable disease control, to assess professional opinion on the use of rapid tests in the diagnosis of food poisoning. RESULTS: Good test performance levels were observed with rapid test methods, especially for polymerase chain reaction (PCR) assays. The estimated levels of diagnostic accuracy using the area under the curve of the summary receiver operating characteristic curve was very high. Indeed, although traditional culture is the natural reference test to use for comparative statistical analysis, on many occasions the rapid test outperforms culture, detecting additional 'truly' positive cases of food-borne illness. The significance of these additional positives requires further investigation. Economic modelling suggests that adoption of rapid tests in combination with routine culture is unlikely to be cost-effective, however, as the cost of rapid technologies decreases; total replacement with rapid technologies may be feasible. CONCLUSIONS: Despite the relatively poor quality of reporting of studies evaluating rapid detection methods, the reviewed evidence shows that PCR for Campylobacter, Salmonella and E. coli O157 is potentially very successful in identifying pathogens, possibly detecting more than the number currently reported using culture. Less is known about the benefits of testing for B. cereus, C. perfringens and S. aureus. Further investigation is needed on how clinical outcomes may be altered if test results are available more quickly and at a greater precision than in the current practice of bacterial culture.

Serological responses to Cryptosporidium in human populations living in areas reporting high and low incidences of symptomatic cryptosporidiosis.

One approach to investigating differences in the reported incidence of disease is to measure the extent of exposure to the organism in question by testing for a specific antibody response. IgG responses to Cryptosporidium sporozoite antigens of low molecular size in adults have been shown to be consistent and of sufficient intensity to act as reliable markers of exposure. This study used a western blot procedure to investigate the relative intensity of IgG antibody responses to the 15/17-kDa Cryptosporidium sporozoite antigen complex and the 27-kDa antigen in sera from two cities in north-west England: Liverpool (low numbers of clinical cases reported) and Preston (high numbers reported). The intensity of antibody response to the 15/17-kDa antigen complex was significantly greater in the Liverpool sera, but there was no significant difference in intensity of response to the 27-kDa antigen. The relationship between diagnosed and reported cryptosporidiosis infections and infections identified by serological testing is complex, but could indicate a protective effect resulting from either exposure to non-pathogenic strains or from repeated low-level exposure to pathogenic strains.

Treatment of cryptosporidiosis in immunocompromised individuals: systematic review and meta-analysis.

Cryptosporidium is a common cause of gastroenteritis and is associated with severe life-threatening illness among immunocompromised individuals. This review aimed to assess the efficacy of interventions for the treatment and prevention of cryptosporidiosis among immunocompromised patients. A search of Medline, Embase and other electronic databases was carried out up to August 2005. Two reviewers independently extracted data and assessed study quality. The relative risk for each intervention was calculated. Seven trials involving 169 participants were included. Nitazoxanide and paramomycin were associated with a relative risk (RR) of reduction in the duration and frequency of diarrhoea of 0.83 [95% confidence interval (CI) 0.36, 1.94] and 0.74 (95% CI 0.42, 1.31), respectively, showing no evidence of effectiveness. Nitazoxanide led to significant evidence of oocyst clearance compared with placebo with a RR of 0.52 (95% CI 0.30, 0.91). The effect was not significant for HIV-seropositive participants (RR 0.71, 95% CI 0.36, 1.37). HIV-seronegative participants on nitazoxanide had a significantly higher relative risk of achieving parasitological clearance of 0.26 (95% CI 0.09, 0.80) based on a single study. No other intervention was associated with either a reduction in diarrhoea, mortality or a significant parasitological response. This review confirms the absence of evidence for effective agents in the management of cryptosporidiosis. The results indicate that nitaxozanide reduces load of parasites and may be useful in immunocompetent individuals. The absence of effective therapy highlights the importance of preventive interventions in this group of patients.

Prevention and treatment of cryptosporidiosis in immunocompromised patients.

BACKGROUND: Cryptosporidiosis is a disease that causes diarrhoea lasting about one to two weeks, sometimes extending up to 2.5 months among the immunocompetent and becoming a more severe life-threatening illness among immunocompromised individuals. Cryptosporidium is a common cause of gastroenteritis. Cryptosporidiosis is common in HIV-infected individuals. OBJECTIVES: The objective of the review was to assess the efficacy of interventions for the treatment and prevention of cryptosporidiosis among immunocompromised individuals. SEARCH STRATEGY: We searched the following databases for randomised controlled trials up to August 2005: Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, AIDSLINE, AIDSearch, EMBASE, CINAHL, Current Contents, Geobase, and the Environmental Sciences and Pollution Management. SELECTION CRITERIA: Randomised controlled trials that compared the use of any intervention to treat or prevent cryptosporidiosis in immunocompromised persons were included. The outcome measures for treatment studies included symptomatic diarrhoea and oocyst clearance. DATA COLLECTION AND ANALYSIS: Two reviewers independently assessed the trials for quality of randomisation, blinding, withdrawals, and adequacy of allocation concealment. The relative risk for each intervention was calculated using a random effects model. MAIN RESULTS: Seven trials involving 169 participants were included. There were 130 adults with AIDS enrolled in five studies. Evidence of significant heterogeneity was present. There was no evidence for a reduction in the duration or frequency of diarrhoea by nitazoxanide (RR 0.83 (95% CI 0.36-1.94)) and paramomycin (RR 0.74 (95% CI 0.42-1.31)) compared with placebo. Nitazoxanide led to a significant evidence of oocyst clearance compared with placebo among all children with a relative risk of 0.52 (95% CI 0.30-0.91). The effect was not significant for HIV-seropositive participants (RR 0.71 (95% CI 0.36-1.37)). HIV-seronegative participants on nitazoxanide had a significantly higher relative risk of achieving parasitological clearance of 0.26 (95% CI 0.09-0.80) based on a single study. The single study comparing spiramycin with placebo found no significant difference in reduction of the duration of hospitalisation (mean difference -0.40 days (95% CI -6.62-5.82)) or in mortality between the two arms of the trial (RR 0.43 (95% CI 0.04-4.35)). One study assessed the role of bovine dialyzable leukocyte extract, reporting a relative risk for decreased stool frequency of 0.19 (95% CI 0.03-1.19), while another compared bovine hyperimmune colostrum with placebo and found no evidence for improvement of stool volume (RR 3.00 (95% CI 0.61-14.86)) or in oocyst concentration per ml of stool (RR 0.27 (95% CI 0.02-3.74)). No studies were found that assessed prevention. AUTHORS' CONCLUSIONS: This review confirms the absence of evidence for effective agents in the management of cryptosporidiosis. The results indicate that nitaxozanide reduces the load of parasites and may be useful in immunocompetent individuals. Due to the seriousness of the potential outcomes of cryptosporidiosis, the use of nitaxozanide should be considered in immunocompromised patients. The absence of effective therapy highlights the need to ensure that infection is avoided. Unfortunately, evidence for the effectiveness and cost-effectiveness of preventive interventions is also lacking.

Changes of neoplasm concentration with geographical co-ordinates.

We investigated the regional differences in diversity--from another respect concentration--of causes of cancer mortality in England and Wales. Statistical analyses of published mortality data were done, using the jackknifed estimate of the Shannon index, for each region, sex and age group and year of death. In males diversity of cancer death causes is secularly increasing whilst it is decreasing in females. Latitude was negatively associated with diversity in male 45+ year age groups and longitude negatively associated with diversity in male 65+ age groups. Although, there were some significant associations in the female groups, there was no general trend across age groups as found in males. These trends remained after accounting for regional variation in past smoking behaviour. We suggest that the observed patterns may be related to prior occupational exposures and non-identified environmental and socioeconomical factors. It is concluded that techniques drawn from population ecology have a potential value in epidemiological studies of human disease. Ecological methods by themselves are likely to be of value in hypothesis generation rather than hypothesis testing.

Climate change and waterborne and vector-borne disease.

This paper considers the potential impact on human health from waterborne and vector-borne infections. It concentrates on the impact of two possible changes to climate; increased frequency of heavy rainfall events, with associated flooding and increased temperature. Flooding is associated with increased risk of infection in developing nations but not in the West unless water sources are compromised. There have been numerous reported of outbreaks that followed flooding that led to contamination of underground sources of drinking water. Heavy rainfall also leads to deterioration in the quality of surface waters that could adversely affect the health of those engaged in recreational water contact. It is also concluded that there may be an increase in the number of cyanobacterial blooms because of a combination of increased nutrient concentrations and water temperature. It is considered unlikely that climate change will lead to an increase in disease linked to mains drinking water, although private supplies would be at risk from increased heavy rainfall events. Although increased temperature could lead to climatic conditions favourable to increases in certain vector-borne diseases such as malaria, the infrastructure in the UK would prevent the indigenous spread of malaria.

A community survey of self-reported gastroenteritis undertaken during an outbreak of cryptosporidiosis strongly associated with drinking water after much press interest.

We took the opportunity provided by a large outbreak of cryptosporidiosis in the North West of England to investigate the potential impact of recall bias on strength of association and on estimates of outbreak size. We conducted a community-based survey of 4 towns within the outbreak area and 4 control towns. A postal questionnaire was sent to 120 homes, chosen at random from the local telephone directory, in each of the 8 towns. Although not statistically significant, the prevalence of self-reported diarrhoeal disease was marginally higher in the control towns than in the outbreak towns. There was a very strong association between self-reported diarrhoea and drinking water consumption in both control and outbreak areas. The impact of recall bias in outbreak investigations is much greater than previously thought. Identification of the cause of outbreaks should not be based solely on case-control studies conducted after the press has reported the outbreak. Such evidence is likely to be unreliable and give falsely significant associations between water consumption and disease.