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FACTS ABOUT E. coli O157:H7:
Toxin-producing Escherichia coli

Several strains of the bacterium E. coli cause a variety of diseases in humans and animals. E. coli O157:H7 is a type associated with a particularly severe form of human disease E. coli O157:H7 is one of the most virulent (highly infectious) pathogens known to enter the world food supply. It causes diarrhoea, abdominal pain, and in some cases, intestinal bleeding and kidney failure.

The initial symptoms of E. coli O157:H7 illness generally occur within two days after eating contaminated food, though periods of three to five days have been reported. Symptoms increase in intensity during the next 24-48 hours, lasting from four to 10 days. Less than ten E. coli O157:H7 cells may be enough to cause illness in humans. A low infectious dose of two to 2,000 cells has been associated with outbreaks of food borne illness. E coli O157:H7 can survive in acidic environments that are lethal to other pathogens, such as in fermented foods like sausage and apple cider. Though potentially deadly to humans, E. coli O157:H7 is not pathogenic to cattle.

A single cow, or a number of cattle within the same herd, may contain more than one strain of E. coli O157:H7. Some strains are thought to have greater acid tolerance than others.

The source of E. coli O157:H7 contamination on carcasses is likely due to fecal contamination during animal production and slaughter operations. Carcasses may become contaminated during hide removal or by cross-contamination with equipment and workers’ hands. HACCP (food safety control) systems in processing plants cannot eliminate E. coli O157:H7 from foods unless a treatment is added that will kill the pathogen, such as heat pasteurisation or irradiation. Current research shows that competitive exclusion has the potential to eliminate E. coli O157:H7 from cattle before slaughtering. Competitive exclusion involves the use of non-pathogenic micro-organisms to outgrow pathogens in the gastrointestinal tracts of animals.

If swallowed, faecal contaminated water in freshwater swimming areas may cause E. coli O157:H7 infection in both cattle and humans. Fresh manure used to fertilise garden fruits and vegetables may contaminate them with E. coli O157: H7. The largest reported E. coli O157:H7 outbreak, which caused thousands of illnesses, occurred in Japan in 1996. Radish sprouts were implicated as the source of infection.

Though ground beef has been most often associated with E. coli O157:H7 outbreaks in the United States, other implicated foods include raw milk, apple cider, dry-cured salami, lettuce, produce from manure-fertilised gardens, potatoes, radish and alfalfa sprouts, yoghurt, sandwiches, and water.

E. coli O157:H7 causes hemorrhagic colitis, which begins with watery diarrhea and severe abdominal pain and rapidly progresses to passage of bloody stools. It has been associated with HUS, a life-threatening complication of hemorrhagic colitis characterized by acute kidney failure that is particularly serious in young children. E. coli O157:H7 is found in cattle, but there may be other reservoirs; the dynamics of E. coli O157:H7 in food-producing animals are not well understood. Approximately 25,000 cases of foodborne illness can be attributed to E. coli O157:H7 every year, with as many as 100 deaths resulting. E. coli O157:H7 outbreaks have recently been associated with ground beef, raw milk, lettuce, and minimally processed and fresh fruit juices. An outbreak in the fall of 1996 in three western states and British Columbia was associated with unpasteurized apple juice and sickened 66 people, causing the death of one child.

Estimations are that in the United Sates, between two and eight million people become sick and 200 to 800 die because of campylobacter every year. The infection has also been linked to Guillain-Barr syndrome, which causes severe nerve damage. Studies indicate that 20 to 40 percent of the 5,000 annual cases of Guillain-Barre follow a bout with campylobacter.

More than 70 per cent of chickens and up to 100 per cent of turkeys are infected with it. Campylobacter also infects cattle, hogs and sheep.

Heat kills campylobacter even more readily than salmonella, so temperatures used to control salmonella will also be effective against campylobacter.

Ciguatera fish poisoning in humans is most commonly caused by eating carnivorous fish contaminated by a toxin produced by the dinoflagellate Gambierdiscus toxicus. The toxin bio-accumulates through the food chain, and carnivorous fish such as barracuda, red snappser, grouper, sturgeon, and amberjack are usually the most commonly involved.

In Canada, most cases of ciguatera poisoning reported in the past have involved Canadians who ate fish in the Caribbean while on holiday. These cases have implicated grouper in the Dominican Republic, kingfish in Jamaica, and barracuda in Haiti. A fish casserole caused the illness in 57 people during a trip to Cuba.

Ciguatera poisonings have also been reported as a result of importing certain fish. Dried barracuda brought back from Jamaica in 1983 and imported red snapper bought in an Ontario market were identified sources.

On September 29, 1997 at the 37th Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC) in Toronto, Canada, Dr. David Relman presented a review and update of current knowledge of cyclosporiasis as an emerging infectious disease. He reminded listeners that, variably acid-fast organisms with an approximate diameter of 8-10 microns resembling large forms of Cryptosporidium have been identified in faecal samples from patients exhibiting episodes of watery diarrhoea since the 1980s. It was in 1993 that Ortega and Sterling published a report identifying the organism as a Cyclospora sp. in the New England Journal of Medicine. Relman himself has generated data for the sequence of ribosomal RNA genes for this organism, and confirmed its identity as a Cyclospora sp.

Dr. Relman described a typical clinical course for infected patients as intermittent watery diarrhoea after a 7 day incubation period. Untreated disease can lead to anorexia, fatigue and weight loss lasting for weeks in immunocompetent hosts, and even longer in immunocompromised hosts. The infection can be successfully treated with trimethoprim/sulfamethoxazole. Relapses are not uncommon in treated patients. No suitable alternative therapy has been identified for sulpha-allergic persons. There are no data for the efficacy of trimethoprim alone.

Dr. Relman offered additional insight into the epidemiology of cyclosporiasis. Infection or colonization of asymptomatic persons is common (endemic) in Asia (especially in Neplighttouchprogrammingal), Peru and Haiti, but uncommon in Tanzania (the latter based on comments offered during the question and answer session). In the US approximately 0.5% of fecal samples from symptomatic persons will contain Cyclospora.

This low incidence suggests that there are many naive hosts in North America, and Relman suggests that this may in part explain the relatively recent emergence of this disease in North America. Last year’s documented outbreaks involved Guatemalan raspberries, while in 1997, mesclun lettuce and basil from other sources as well as Guatemalan raspberries have been implicated. Between 1,600 and 1,700 cases have been reported in the US and Canada this year.

Hepatitis A (HAV) is a virus that infects the liver and causes hepatitis A, an illness with an abrupt onset that can include fever, malaise, nausea, abdominal discomfort, dark urine and jaundice after a prolonged incubation period (for example, more than two months). In children less than six years old, most infections (70 percent) are asymptomatic, but in older children and adults, infection is usually symptomatic, with jaundice occurring in more than 70 percent of patients. Signs and symptoms of Hepatitis A usually last more than two months, but there are no chronic consequences. About 130,000 infections with HAV and 100 deaths occur every year in the U.S..

The primary mode of transmission for HAV is person-to-person by the fecal-oral route. (Preparing food with unwashed hands after using the toilet or changing diapers, is a typical faecal-oral route) Recognized foodborne Hepatitis A outbreaks account for only 2 to 5 percent of Hepatitis A cases reported in the U.S. every year, most of which are caused by an infected food handler.

Outbreaks caused by foods contaminated before preparation have been associated with widely distributed products such as shellfish, lettuce, frozen raspberries and frozen strawberries. Hepatitis A can be prevented by good personal hygiene and safe food-handling practices.

Salmonella bacteria cause diarrhoea and systemic infections, which can be fatal particularly in susceptible persons, such as the immunocompromised, the very young and the elderly. Animals used for food production are common carriers of Salmonella, which can subsequently contaminate foods such as meat, dairy products and eggs. Foods often implicated in outbreaks include poultry and poultry products, meat and meat products, dairy products, egg products, seafood and fresh produce. An estimated 800,000 to four million infections occur every year in the U.S.

Between 128,000 and 640,000 of those infections are associated with Salmonella enteritidis in eggs. Over the past decade, more than 500 outbreaks have been attributed to Salmonella enteritidis, resulting in more than 70 deaths. In 1994 an estimated 224,000 people became ill from consuming ice cream in one outbreak alone.