Outbreak of Vero cytotoxin-producing Escherichia coli O157 in a child day care facility

In December 1998, an outbreak of Vero cytotoxin-producing Escherichia coli (VTEC) O157 in a crèche affected ten out of 45 children and one out of five staff members. Eight cases were symptomatic and three were asymptomatic. There were two asymptomatic adult family contacts of child cases. All specimens were identified as VTEC O157:H7, phage type 32. None of the cases were seriously ill and none developed haemolytic uraemic syndrome (HUS). One child continued to excrete the organism for 14 weeks. The origin of the outbreak was not found but epidemiological investigation was suggestive of person-to-person spread. All children and staff were screened and excluded from the crèche until microbiological clearance was obtained. An inspection of the crèche revealed overcrowding and inadequacies in cleaning and in the food preparation facilities. These problems were remedied before children were re-admitted to the crèche. This outbreak demonstrates the ease with which VTEC O157 can be transmitted between small children. Two specific features of this outbreak were notable: (1) the mild self-limiting nature of the illness and (2) the prolonged shedding of the bacterium by one child.

Use of phenotyping and genotyping to verify transmission of Escherichia coli O157:H7 from dairy farms

A total of 80 human infections by Escherichia coli O157:H7 were documented in Finland in 1997 and 1998. Most were sporadic and their sources undetermined. Five cases not associated with one another, one of which led to secondary transmission within a family, could be traced to five different dairy farms. These five case patients (age range 2-17 years, median age 3 years) were hospitalised with bloody diarrhoea; two of them developed haemolytic uraemic syndrome. All nine human isolates obtained were sorbitol negative, carried the verocytotoxin 2 and eae genes, and produced verocytotoxin and enterohaemolysin. The phage and pulsed-field gel electrophoresis types of the human and bovine isolates from the corresponding farms were indistinguishable. The cattle (20-70 animals per farm) were monitored for up to 2 years after the human cases. The proportion of cattle excreting the type that caused the human infections varied from 3.2 to 66.7% when sampled soon after the human cases, and from 0.0 to 5.3% about a year or so later. On most of the farms, the animals excreted the pathogen intermittently. On one farm, Escherichia coli O157 isolates with other characteristics were also occasionally isolated. Although the infections were traced back to the farms, it could not be established whether the source was unpasteurised milk or direct or indirect contact with cattle. The results of this study emphasise the need for special recommendations for children visiting or living on a farm to prevent these infections.

Extraintestinal pathogenic Escherichia coli: "the other bad E coli"

Extraintestinal pathogenic Escherichia coli (ExPEC), the specialized strains of E coli that cause most extraintestinal E coli infections, represent a major but little-appreciated health threat. Although the reasons for their evolution remain mysterious, by virtue of their numerous virulence traits ExPEC clearly possess a unique ability to cause disease outside the host intestinal tract. Broader appreciation of the existence and importance of ExPEC and better understandings of their distinctive virulence mechanisms, reservoirs, and transmission pathways may lead to effective preventive interventions against the morbid and costly infections ExPEC cause.

The public health significance of VTEC O157

Surveillance of human VTEC O157 has been reported in several countries, based on laboratory evidence. The incidence is generally less than 10 per 100000 (the highest incidence is in children), with regional variations and a marked seasonality. Laboratory selection criteria and reporting have contributed to, but cannot entirely explain, variations within and between countries. Surveillance data and outbreaks in definable cohorts indicate that the spectrum of illness ranges from diarrhoea through acute bloody diarrhoea, with about 5% of cases developing haemolytic uraemic syndrome; less than 50% of patients report frank blood in their stools. Studies of sporadic cases have associated illness with beef products (particularly if undercooked and eaten outside the home), cooked sliced meat meals and contact with a household member with diarrhoea. Outbreaks have been attributed to contaminated foods (including beefburgers) and water, animal contact and person-to-person spread. Secondary transmission by the primary case in a household is of particular concern, and household transmission has been estimated at 4%, with patients excreting for around 10 days following onset. Recommendations for control have highlighted measures on farms, in slaughterhouses, retail and catering food premises, and in the home.

A cluster of Escherichia coli O157: nonmotile infections associated with recreational exposure to lake water

OBJECTIVES

To identify cases and determine risk factors for an outbreak of Escherichia coli (E. coli) O157: nonmotile (NM) infections in children attending a summer day care program in California.

METHODS

The authors conducted a retrospective cohort study; the cohort comprised first and second graders who attended the day care program during the last week in August 1999. Shiga toxin testing and molecular subtyping using pulsed-field gel electrophoresis were performed on isolates. Lake water, lake bottom sediment samples, and waterfowl feces from the lake environs were cultured for E. coli O157.

RESULTS

Three cases of Shiga toxin-producing E. coli O157: NM infections with matching pulsed-field gel electrophoresis patterns and four probable cases were found. Children who swallowed more than a mouthful of water had a higher attack rate than those who swallowed less than a mouthful or none at all (43% vs. 10%, relative risk = 4.43, 95% confidence interval 1.12, 17.50).

CONCLUSIONS

E. coli O157: NM infections were associated with swallowing water from a freshwater lake. Potential sources of contamination include feces from humans, cattle, or deer. This outbreak illustrates the value in screening patients with diarrhea for E. coli O157, submitting isolates to public health laboratories, and using molecular techniques to identify related cases. Outbreaks associated with contaminated freshwater could be averted by prevention and early detection of contamination.

Escherichia coli O157:H7 infection of calves: infectious dose and direct contact transmission

Cattle are considered to be a reservoir host of Escherichia coli O157:H7 and contaminated foods of bovine origin are important vehicles of human infection. In this study, the susceptibility of calves to experimental E. coli O157:H7 infection following low oral exposures was determined. Two of 17 calves exposed to very low (< 300 c.f.u.) doses, and 3 of 4 calves exposed to low (< 10,000 c.f.u.) doses, subsequently excreted the challenge strains in their faeces. All calves (n = 12) sharing isolation rooms with calves that excreted the challenge strain in their faeces similarly began faecal excretion of the same strains within 21 days or less. The identity between the challenge strains and the strains excreted in calf faeces was confirmed by restriction digestion electrophoretic patterns using pulsed field gel electrophoresis. Calves shed E. coli O157:H7 in their faeces after very low dose exposures at concentrations ranging from < 30 to > 10(7) c.f.u./g, and for durations similar to the values previously reported for calves challenged by larger doses. The susceptibility of calves to infection following very low exposures or direct contact with infected calves has important implications for programmes for pre-harvest control of this agent.

Escherichia coli O157:H7: etiology, clinical features, complications, and treatment

In recent years, Escherichia coli (E. coli) O157:H7 has developed into an emerging cause of foodborne illness. It has been identified as the leading cause of post-diarrheal hemolytic-uremic syndrome (HUS) and acute renal failure in infancy and childhood. This article examines, the etiology, clinical features, complications, and treatment of this illness. Prevention strategies are also presented as well as a disaster management case study.

[Neonatal bacterial infection by maternal-fetal contamination: for a change in approach? 2. Uncertainties and proposals]

Based on a critical analysis of the literature, it is clear that even though mortality has decreased to 10-15%, the prevalence of neonatal bacterial infections remains dramatically stable. Precise risk factors can be identified in most cases of neonatal infection, but remain uncertain in many others: Streptococcus agalactiae is found in only 40% of the cases of sepsis; Escherichia coli, Haemophilus influenzae, Pneumococcus, and group A Streptococcus strains should also be considered for a real prophylactic strategy; context (prematurity), lack of a consensual attitude for intrapartum strategies; management schemes for asymptomatic neonates. Based on these observations, we make proposals for a realistic attitude for everyday practice based on risk factors, maternal and neonatal bacterial sampling procedures, and modalities for neonatal antibiotic therapy.

Escherichia coli O157:H7 in free-ranging deer in Nebraska

In order to determine the prevalence and distribution of the human pathogen, Escherichia coli O157:H7, in free-ranging deer, hunters were asked to collect and submit fecal samples from deer harvested during a regular firearm season (14-22 November 1998). Prior to the season, 47% of the hunters with permits in the southeastern Nebraska (USA) study area indicated a willingness to participate in the study. Approximately 25% of successful hunters in the area submitted deer fecal samples. Escherichia coli O157:H7 was cultured from four (0.25%) of 1,608 total samples submitted. All of the fecal samples that were properly identified (1,426) and all that were positive for E. coli O157:H7 were from white-tailed deer (Odocoileus virginianus). We were unable to detect a statistically significant geographic distribution pattern of E. coli O157:H7. The presence of E. coli O157:H7 in the feces of free-ranging deer has implications not only for hunters, consumers of venison, and others in contact with deer or deer feces, but also for the development of strategies aimed at reducing and/or controlling this pathogen in water sources and domestic livestock.

Modelling the vector pathway and infection of humans in an environmental outbreak of Escherichia coli O157

Quantifying the transfer of Escherichia coli O157 from the environment to humans is essential for understanding outbreaks, establishing the infectious dose of the organism and proposing safeguards. We modelled the pathogen loading shed onto a field by sheep immediately prior to a scout camp where 18 scouts and two adults were infected with E. coli O157. We estimated the dose ingested (4-24 organisms) which is in agreement with the low infective dose reported previously for this organism in food outbreaks. These data closely fit a surrogate Shigella dose-response model which can be used as a basis for risk assessment.

[Hemolytic-uremic syndrome: microbiological aspects]

Escherichia coli O157: H7 became an important pathogen starting in the early 1980s. It has caused epidemics and sporadic cases of often bloody diarrhea which may progress to severe hemolytic and uremic syndrome or thrombotic thrombocytopenia purpura. E. coli O157: H7 is mainly transmitted in food, water and interhuman transmission, but direct animal-to-man transmission has also been documented. E. coli O157: H7 can adhere tightly to the enterocyte brush border (eae gene) and produce verotoxins or Shiga-like toxins and hemolysine (ehxA gene). Diagnosis of E. coli O157: H7 infections is based on evidencing the germ in stools and/or by identifying the genes coding for verotoxins or by serology which increased serum titre of specific antilipopolysaccharide antibodies. Antidiarrheal drugs and antibiotics have little place in the treatment of bloody diarrhea. This public health problem, requires careful identification of animal reservoirs and improved population education in food hygiene.

Environmental sources and transmission of Escherichia coli O157 in feedlot cattle

A study was conducted in 2 feedlots in southern Alberta to identify environmental sources and management factors associated with the prevalence and transmission of Escherichia coli O157:H7. Escherichia coli O157:H7 was isolated in preslaughter pens of cattle from feces (0.8%), feedbunks (1.7%), water troughs (12%), and incoming water supplies (4.5%), but not from fresh total mixed rations. Fresh total mixed rations did not support the growth of E. coli O157:H7 and E. coli from bovine feces following experimental inoculation. Within a feedlot, the feces, water troughs, and feedbunks shared a few indistinguishable subtypes of E. coli O157:H7. A few subtypes were repeatedly isolated in the same feedlot, and the 2 feedlots shared a few indistinguishable subtypes. The prevalence of E. coli O157:H7 in water troughs of preslaughter cattle in 1 feedlot was associated with season, maximum climatic temperatures the week before sampling; total precipitation the week before sampling, and coliform and E. coli counts in the water trough.

Infection transmission system models for microbial risk assessment

Chemical risk assessments often focus on measuring exposure as if individuals were subject only to exogenous environmental sources of risk. For infectious diseases, exposure might not only depend on exogenous sources of microbes, but also on the infection status of other individuals in the population. For example, waterborne infections from agents such as Cryptosporidium parvum and Escherichia coli: O157:H7 might be transmitted from contaminated water to humans through drinking water; from interpersonal contact; or from infected individuals to the environment, and back to other susceptible individuals. These multiple pathways and the dependency of exposure on the prevalence of infection in a population suggest that epidemiological models are required to complement standard risk assessments in order to quantify the risk of infection. This paper presents new models of infection transmission systems that are being developed for the US Environmental Protection Agency as part of a project to quantify the risk of microbial infection. The models are designed to help inform water treatment system design decisions.

Cattle water troughs as reservoirs of Escherichia coli O157

Environmental survival of Escherichia coli O157 may play an important role in the persistence and dissemination of this organism on farms. The survival of culturable and infectious E. coli O157 was studied using microcosms simulating cattle water troughs. Culturable E. coli O157 survived for at least 245 days in the microcosm sediments. Furthermore, E. coli O157 strains surviving more than 6 months in contaminated microcosms were infectious to a group of 10-week-old calves. Fecal excretion of E. coli O157 by these calves persisted for 87 days after challenge. Water trough sediments contaminated with feces from cattle excreting E. coli O157 may serve as a long-term reservoir of this organism on farms and a source of infection for cattle.

Epidemiological investigation of the central Scotland outbreak of Escherichia coli O157 infection, November to December 1996

On Friday, 22 November 1996, the microbiologist at a hospital in Lanarkshire, Scotland, identified presumptive Escherichia coli O157 in faecal specimens submitted by three patients with bloody diarrhoea, and confirmed its presence in one. Over the next 6 h, 12 more potential cases were identified. Investigations first indicated then confirmed a single food premises as the source of infection. Effective control measures were applied promptly. The outbreak was declared over on 20 January 1997, by which time 512 cases had been identified, and infection with the outbreak strain confirmed in 279. Twenty deaths occurred in cases during the outbreak and there were two more in cases during 1997. Seventeen of these deaths resulted from the outbreak. This paper describes the outbreak's epidemiological investigation, referring to other investigations, and control measures, where appropriate.

Emerging food-borne pathogens

The epidemiology of foodborne diseases is changing. While in many developing nations the efficient treatment of diarrhoeal diseases through oral rehydration has probably led to the prevention of many food related deaths, the underlying problems have not been solved. In these countries, the disease incidence of food-and waterborne disease is still increasing, and now data from other parts of the world indicate that new foodborne pathogens have emerged as important public health problems. Over the last two decades, bacterial infections caused by Campylobacter and enterohaemorrhagic Escherichia coli have emerged, well-recognized pathogens, such as Salmonella eoteritidis, have increased dramatically in disease incidence and important foodborne pathogens have become increasingly resistant to antimicrobial agents. The future strategy for prevention of foodborne disease should be founded in scientifically based evaluations of the whole food production chain 'from farm to table', including a description of the most important (risk) factors. Epidemiological studies of outbreaks as well as sporadic cases should be aimed at a better understanding of these factors. In terms of public health importance of the problem, the focus should be on the size of the problem, and the potential for improvement. The indications are that both in developed and developing countries there is significant potential for an improvement of the situation. With this aim in mind, international effort should focus on scientific assessments of the potential for risk reduction under different regional conditions.