0157:H7 is one of hundreds of strains of the bacteria Escherichia coli. Although most strains are harmless and live in the intestines of healthy humans and animals, this particular strain produces a powerful toxin that can cause severe illness. The combination of letters and numbers in the name of the bacteria refers to the specific markers on its surface and distinguishes it from other types of E. coli.
Persons who are infected with this bacteria often develop severe bloody diarrhea with abdominal cramps, although sometimes the infection causes non-bloody diarrhea or no symptoms. Vomiting occurs occasionally. Fever is often low-grade or absent. Symptoms generally begin about 3-4 days after exposure and can last several days.
In some persons, particularly children under five years of age and the elderly, the infection can also cause a complication called hemolytic uremic syndrome (HUS), in which the red blood cells are destroyed and the kidneys fail. About 2-7% of infections with E. coli 0157:H7 lead to this complication.
Infection with E. coli 0157:H7 can be diagnosed by a stool culture. Some laboratories do not test for E. coli 0157:H7 so physicians must specifically request a culture for this bacteria. In general, 3-5 days are necessary to perform the test after the sample has been received. Most persons recover within a few days without any specific treatment. There is no evidence that antibiotics are helpful and it is thought that treatment with some antibiotics may precipitate kidney complications. Antidiarrheal agents are not recommended. As with all types of diarrhea, it is important to avoid dehydration by drinking plenty of fluids.
HUS is a serious disease that affects the kidneys and blood clotting system. Physicians use the results of several tests and medical evaluation to determine if a person has HUS. These tests include kidney function, blood clotting factors, and blood counts. Treatments for HUS include blood transfusions and kidney dialysis.
E. coli 0157:H7 can be found in the intestines of healthy cattle. Meat can become contaminated as a normal part of the slaughtering process. Eating raw or undercooked meat contaminated with E. coli 0157:H7 can cause infection. Bacteria present on a cow's udders or on equipment can also get into raw milk. Consumption of raw (unpasteurized) milk may also result in infection.
Other known sources of E. coli 0157:H7 infection are consumption of contaminated foods such as sprouts, unpasteurized juice, dry cured salami, and contaminated water.
Bacteria in stools of infected persons can be passed from one person to another if hygiene or hand washing habits are inadequate. This type of spread is especially likely in young children who are not toilet trained. It is also likely that family members and playmates have a much higher risk of becoming infected. Careful attention to good hand washing and hygiene will help prevent others from getting infected.
E. coli 0157:H7 is usually cleared from an infected person's stool within a week after diarrhea onset. In some children this bacteria may persist in their stool for 2-4 weeks.
When meat is contaminated with E. coli 0157:H7, it usually occurs on the meat product's outside surface. When you cook a steak or roast, the outside of the meat is heated sufficiently so that pathogens on the surface are easily killed. Because ground meat is made by mixing, numerous small portions of the surface area (and potentially the bacteria) are spread throughout the product. Therefore it is important to cook ground beef throughout so that none of the bacteria survive. In addition, solid muscle meats that have been mechanically tenderized, injected or 'pinned' may have had surface bacteria pushed into internal parts of the product. Therefore, these products should also be thoroughly cooked to 160F, using a meat roasting thermometer.
E. coli 0157:H7 bacteria can survive both refrigeration and freezer storage. It is not known what level of E. coli 0157:H7 causes infection but the number is considered to be low. For this reason, proper food handling and preparation techniques are essential. Use the following methods as controls against infection:
Dairy & Food Inspection Division