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Escherichia coli O157:H7 in New Zealand
Background
What is E. coli O157:H7 infection?
E. coli are bacteria that normally live in the intestines of humans and animals. Although, most strains of this bacterium are harmless, several are known to produce toxins that can cause diarrhoea. One particular E. coli strain called O157:H7 can cause severe diarrhoea and kidney damage.
Who gets E. coli O157:H7 infection?
Anyone of any age can become infected with E. coli O157:H7, but children and elderly persons are more likely to develop serious complications.
How does one get infected with E. coli O157:H7?
The bacteria live in the intestines of some healthy cattle, sheep and pigs as well as deer and seagulls. Eating undercooked meat, usually minced meat, contaminated during the slaughter process has historically been blamed for most O157 infections. However, it is now well recognized that eating some raw vegetables, drinking untreated water and unpasteurised milk, and handling farm animals that are shedding the pathogen are perhaps more frequent sources of infection. Person-to-person transmission can occur if infected people do not wash their hands after using the toilet.
What are the symptoms of E. coli O157:H7 infection?
People infected by E. coli O157:H7 can develop a range of symptoms. Some infected people may have mild diarrhoea whereas others do not exhibit any symptoms. Most identified cases develop severe diarrhoea and abdominal cramps. Blood is often seen in the stool. Usually little or no fever is present. In severe cases, usually in infants and the elderly, kidneys fail, a condition known as haemolytic uremic syndrome (HUS).
How soon after the exposure do symptoms appear?
The symptoms usually appear about three days after exposure, with a range of one to nine days.
What is the treatment for infection with E. coli O157:H7?
Most people recover without antibiotics or other specific treatment in five to 10 days. Antibiotic treatment is also usually effective, although in rare cases may exacerbate the disease.
What complications can result from infection with E. coli O157:H7?
In some people, particularly children under five years of age, the infection can cause a complication called haemolytic uremic syndrome (HUS). This is a serious disease in which red blood cells are destroyed and the kidneys fail. Transfusions of blood or blood clotting factors as well as kidney dialysis may be necessary. A prolonged hospital stay is often required. While most people with HUS recover completely, it can be fatal.
How can infection with E. coli O157:H7 be prevented?
- Cook all mince thoroughly. Do not eat undercooked mince products.
- Make sure the cooked meat is brown throughout (not pink), and the juices run clear. Preferably check that the internal temperature is higher than 65oC.
- Drink only pasteurised milk and milk products.
- 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 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.
Has there ever been a death in New Zealand from E. coli O157:H7?
There has been one death in 1998 attributed to infection by E. coli O157:H7 but the source of the infection remains unknown.
Dairy Issues
Has E. coli O157:H7 ever been found in New Zealand milk or milk products?
E. coli O157:H7 is present in live animals in New Zealand at what seems to be much lower levels than other countries that have been surveyed. Although E. coli O157:H7 has never been surveyed or found in New Zealand milk and milk products, it has been isolated in all other countries surveyed for the bacteria. There have been cases of human infection in the past in New Zealand, however, these have never been specifically linked to dairy farms, dairy animals, milk or milk products or, indeed, any source.
We would, however expect that E. coli O157:H7 would be isolated if enough samples were taken.
Overseas studies indicate that the numbers of bacteria in the animals fluctuates continually, and the rate of shedding from animals is unpredictable. Therefore, although it can’t be detected, it does not mean that it is not there.
What are we doing about it?
The incidence of E. coli O157:H7 is a food safety issue that is managed by the effective use of pasteurisation of all New Zealand milk and milk products. E. coli O157:H7 is particularly sensitive to pasteurisation so the New Zealand dairy industry uses effective pasteurisation as a mechanism to kill E. coli O157:H7 and all other pathogenic organisms.
Can we eliminate E. coli O157:H7 from our herds?
At present, no – it is present as normal flora of the gut of all ruminants. However vaccination studies are currently underway in Canada that may, if successful, provide a control mechanism in a few years. Herd testing as an option is very expensive and like a number of other pathogens is readily killed by pasteurisation.
Why should all milk for on farm use be pasteurised?
Milk needs to be pasteurised because no matter how carefully the cows are milked, raw milk will carry bacteria derived from the cow as well as the farm environment. There has been significant progress in farm quality practices but there is no way that you can always control the types of bacteria. Raw milk must always be considered a potential risk. Pasteurisation, which is critical to the safety of our processed products, is also essential for the safe use of milk on farms.
Farms that use milk direct from the bulk milk tank for home use are strongly recommended to use a home a pasteurisation method where milk is heated momentarily to 75oC then cooled.
Meat Issues
Meat Perspective for Escerichia coli O157:H7
E. coli O157:H7 was first recognised in 1982 as a foodborne pathogen following two outbreaks of colitis attributed to undercooked hamburgers in the USA. Since then, there have been many outbreaks attributed to food borne infection in other countries, although none in New Zealand.
The source of food borne infections, apart from the well-documented ground beef, has included ham and turkey sandwiches, raw milk, apple cider, radish sprouts, mayonnaise and potatoes. Drinking water, live animals and farms, as well as infected humans have also been implicated in human infection and are regarded as important in the epidemiology of human infection.
E. coli O157:H7 is present in New Zealand and has been isolated from sporadic human cases, the first in October 1993. There have been 219 isolations of E. coli O157 (H7+ & H7-) in humans between October 1993 and March 2001. There has been one death in 1998 attributed to infection by E. coli O157:H7.
The source of infection for all these cases, however, remains unknown. None were specifically identified as foodborne in origin. Ministry of Health investigations of clusters of sporadic cases in the South Auckland/Waikato/Bay of Plenty areas suggested that contact with farm animals and the consumption of untreated water or unpasteurized milk may have been risk factors.
Food that is produced under the existing regulatory regimes, and is available to the general public, has not been implicated in the clusters.
Has E. coli O157:H7 ever been found in New Zealand meat or meat products?
E. coli O157:H7 is present in live animals in New Zealand although at what seems to be a much lower prevalence than other countries that have carried out surveys.
The presence of E. coli O157:H7 in cattle in New Zealand was demonstrated in a study conducted by the Meat Industry Research Institute of New Zealand (MIRINZ). E. coli O157:H7 was detected in the faeces of two of 371 cows from 55 dairy farms tested on arrival at a single slaughterhouse in the Waikato area. A further 160 cattle from the farm of one of the positive animals tested negative for E. coli O157:H7.
MAF Food have carried out three targeted and statistically based microbiological surveys specifically looking for E. coli O157:H7 on carcasses. E. coli O157:H7 was not detected on:
- 600 cattle carcasses from the Waikato/Bay of Plenty area.
- 2400 cattle carcasses across New Zealand over a full processing season
- 500 ovine carcasses across New Zealand over a full processing season
The extremely low prevalence of E. coli O157:H7 on New Zealand beef meat has similarly been demonstrated in the industries ongoing, daily test programme implemented in 1997. E. coli O157:H7 has been detected to date in just two of 110397 cartons of bulk meat tested (one detection remains unconfirmed).
Finally, the University of Otago did not detect E. coli O157:H7, indeed did not detect any enterohaemorrhagic E. coli, in a comprehensive survey of retail meats in Dunedin.
What are we doing about it?
While the regulatory programmes in place in New Zealand to prevent foodborne transmission of E. coli O157:H7 do not guarantee absence of the pathogen in food, evidence suggests that the extensive "preventative" food hygiene programmes covering primary production minimises microbial contamination of food and, hence, the risk to human health. To date, infection in humans appears to be related to sources other than food produced in compliance with the current regulatory regimes.
MAF Food and the New Zealand meat industry continue to monitor New Zealand and overseas research initiatives in order to gain a better understanding of (a) factors that affect shedding of the organism by animals, and hence transmissibility to the food supply, and (b) the effect of methods of preservation (e.g. freezing, chilling, vacuum-packaging) on survivability of E. coli O157:H7.
How can consumers protect themselves?
Consumers can protect themselves from E. coli O157:H7 infection by following two basic food safety rules.
- Bacteria on non-tenderised steaks are generally restricted to the outside surfaces of the meat, and are therefore killed by searing the outside surfaces. In contrast, bacteria are distributed throughout ground/minced beef products, reformed roasts and steaks that have been mechanically tenderised. Consequently, these food items should be adequately cooked throughout. Ideally, the temperature at the core should have exceeded 65°C during cooking. At the very least, the meat at the core of the product should be brown (not pink) with clear juices.
- Because raw foods (including meat) can contain pathogenic bacteria, consumers should make all efforts to avoid cross-contaminating items of food that will not be cooked (e.g. salads) and meat that has already been cooked. Raw food should be well separated from ready-to-eat food. Hands, knives and preparation surfaces (e.g. cutting boards) should be washed with hot water and detergent after contacting any raw foods.
New Zealand Food Safety Authority
68-86 Jervois Quay
PO Box 2835
Wellington
NEW ZEALAND
Phone: +64 4 894 2500
Fax: +64 4 894 2501
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