Escherichia coli (E. coli)
Escherichia coli (E. coli) is a bacterial species that normally lives in the intestines of people and other warm-blooded animals. E. coli constitute about 0.1% of the human and animal gut flora, although it is the predominant bacterium able to grow in the presence of oxygen. Most E. coli are harmless and actually are an important part of a healthy human intestinal tract producing vitamin K and helping to prevent colonization by disease-causing bacteria.
Being residents of the human and animal gut, E. coli can contaminate the farm, water catchment and food processing environment via faeces, and from there can subsequently contaminate foods. Similarly, process workers can contaminate the food processing environment and foods if they do not follow personal hygiene requirements.
Food processing hygiene controls are designed to prevent, or minimise, contamination of food from the environment and workers.
Bacteria that cause human foodborne illness such as Salmonella and Campylobacter also inhabit the gut of food animals and humans, and can contaminate food and the environment via faeces. However, they are infrequently found in faeces of many animals and often at very low levels which makes them very difficult to detect when contamination events have occurred. It is therefore better for companies to look for, and eliminate, faecal contamination in their premises to provide their food safety assurances.
Because E. coli is present in most faeces and at high numbers, monitoring for E. coli (or its wider family “coliforms”) is the most efficient means to detect faecal contamination and is therefore a valuable tool in a company’s armory to detect hygiene deficiencies and provide food safety assurances. E. coli is able to survive outside the body for a period of time which makes it an ideal indicator organism to test environmental samples for faecal contamination.
The detection of E. coli in food therefore simply indicates that the conditions were present that could result in contamination by microbes that can cause foodborne illness. It does not indicate that disease causing organisms are present.
Pathogenic E. coli
Although most strains of E. coli are harmless, there are some types that cause food borne illness and in particular diarrhoea with bloody stools, and can lead to kidney failure. Bacteria that cause illness are termed pathogens. These strains are known as shiga toxin-producing E. coli (STEC); also referred to as verocytotoxigenic E. coli (VTEC) or enterohaemorrhagic E. coli (EHEC).
The pathogenic STECs are generally identified by their serotype. E. coli O157:H7 causes the vast majority of human illnesses, with serotypes O26, O45, O91, O103, O111, O113, O121 and O145 causing human illness here in new Zealand and overseas.
The primary hosts of these serotypes are believed to be cattle and sheep in which they do not cause illness. While historically and internationally they are transmitted to humans through consumption of contaminated foods, such as raw or undercooked ground meat products, raw milk and contaminated raw vegetables and sprouts, regulated food has never been implicated in any human STEC illness in New Zealand. Rather, the vast majority of human illnesses in New Zealand have been associated with farm environments, either through animal contact, consumption of untreated water or raw milk.
Raw meats may be contaminated with STECs. While the risk of infection is minimised by thorough cooking until all parts reach a temperature of 70°C or higher, they may still be transmitted to humans by cross-contamination during food preparation. Again, there is no evidence of foodborne transmission in New Zealand.
Person-to-person transmission can occur if infected people do not wash their hands after using the toilet.
Generally, people infected by STECs will develop mild/severe diarrhoea with stomach cramps in 3-9 days after the organisms are ingested, often with blood in the stools.
Most patients recover within 10 days. However, a small proportion of patients (usually infants and frail elderly) develop life-threatening disease such acute kidney disease. Most people with kidney disease recover completely. However, it can be fatal and two deaths have been attributed to STECs in New Zealand since the early 1990’s; An elderly person in 1998 due to E. coli O113 and another infant in 2009 due to O157.
Persons who experience bloody diarrhoea or severe abdominal cramps should seek medical care. Antibiotics are usually not part of the treatment of patients with STEC disease and may possibly increase the risk of subsequent kidney disease. Treatment usually involves non-specific supportive therapy, including hydration. A prolonged hospital stay is often required.
How can infection with STECs be prevented?
- Cook all minced meat pattys thoroughly. Do not eat undercooked minced products.
- Use a meat thermometer to check that the internal temperature is higher than 70oC. If you don’t have a thermometer, make sure the cooked meat is brown throughout (not pink), and the juices run clear.
- Avoid raw milk, unpasteurized dairy products, and unpasteurized juices.
- Beware of untreated non-tank water at farms.
- Make sure that hands are washed immediately after touching animals and at-risk foods such as raw meat and unpasteurised milk.
- Make sure all people, especially children, wash their hands carefully with soap after using the toilet to reduce the risk of spreading the disease.
- Hands should always be washed carefully with soap and dried before touching food. This is especially important for children in at-risk environments, such as farms, petting zoo's, school fairs, agricultural shows or other places where people are exposed to animal faeces or places where animal faeces have been.
STECs in dairy products
Have STECs ever been found in New Zealand farm animals?
E. coli O157:H7 and other STECs are present in New Zealand in live cattle and sheep, and in their farm environment. Overseas studies indicate that the numbers of bacteria in the animals fluctuates continually, and the rate of shedding from animals is unpredictable. Intensive farming such as the use of feeding pads and herd-homes increases E. coli O157:H7 carriage. However, in general, carriage rates in New Zealand appear to be much lower levels than in other countries that have been surveyed.
It is expected that E. coli O157:H7 and other STECs would be isolated relatively often in the dairy farm environment.
Have STECs ever been found in New Zealand dairy products?
E. coli O157:H7 has been detected in a 2012 MPI survey of New Zealand raw milk but at a very low frequency.
Control of STECs in dairy products?
There are currently no specific measures used on New Zealand farms to control E. coli O157:H7 and other STECs. Commercial vaccines solely for E. coli O157:H7 are now available overseas but are currently not cost effective given that STECs are particularly sensitive to pasteurisation and not one human case has been associated with consumption of regulated food.
Why should milk for on-farm use be pasteurised?
Milk needs to be pasteurised because no matter how carefully the cows are milked and hygienic procedures implemented, raw milk will still potentially carry bacteria able to cause human illness. Raw milk must always be considered a potential risk.
Farms that use milk direct from the bulk milk tank for home use are strongly recommended to use a home pasteurisation method (scolding) where milk is heated momentarily to 75oC then cooled.
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