Where Does It Come From?
At least 44% of all cattle herds may carry the bacterium and as there are no tests to determine which are carriers we must assume that all have E.coli O157. Microbiologists have pinpointed the following food sources: ground beef, ground lamb, unpasteurised milk and products made from unpasteurised milk such as some cheeses. Although banned in Scotland since 1983 unpasteurised milk is still legally sold in England and Wales despite being known to present hazards to the young, the elderly, the immuno compromised and pregnant women. These products are not always labelled as unpasteurised or raw. Pasteurised milk that has failed to reach the correct temperature has also been found to be a source of infection to humans.
Ground (minced) beef is more likely to contain E.coli O157 than a single joint of meat because any contamination on a joint will be on the outside only and thorough cooking should destroy any bacteria. However, when grounding beef the meat from several animals can be used and if only one animal were infected this would result in the whole batch being affected. Also, as the meat is ground, the bacteria are passed from the outside and spread throughout.
The Government recommend that when cooking burgers the internal temperature should reach 70°c and remain at that temperature for at least 2 minutes. Research carried out at Reading University between 1995 and 1998 for the Department of Health indicated that certain of these products could not be cooked to reach an internal temperature of 70ºC before the outside was burnt, which in simple terms means that the product looked as though it was cooked thoroughly but it was not and therefore would not have killed the bacteria where it existed.
There have also been cases caused by eating fruit and vegetables, which have not been thoroughly washed and perhaps contaminated by manure from infected cattle. Soft vegetables (e.g. lettuce) are extremely hard to clean where this bacterium exists.
E.coli O157 can also find its way into water (streams and drinking wells) as a result of run-off from fields containing cattle. When drinking water from an unknown source it is recommended it be boiled before use.
An outbreak of E.coli O157 in 2000 at a Scout camp in Scotland highlighted the dangers of contamination from being in an area previously used by animals when 20 children were affected and one was hospitalised with HUS. In this case sheep had been grazing right up until the camp.
Recreational bathing has also been documented as a source of infection. Unchlorinated pools used by an E.coli O157 sufferer can become contaminated and beaches infected where there has been run-off from animal manure or where sewerage has not been treated properly.
Community farms have also been identified as potential areas of contamination. Following a recent compensation payout of over £2.5 million by the London Borough of Barnet and the "Open Farm" to a child left severely brain damaged following E.coli O157 infection, many authorities are now recommending children under five years of age should not visit. All such farms should have warning signs and hand washing facilities. Eating areas should be separated from all farm animals. At present the Department of Health, the Health & Safety Executive and the National Farmers Union all recommend that children should be prevented from touching calves (as they are particularly likely to be carriers of E.coli O157).