Escherichia coli (in short E. coli) are a large and diverse group of bacteria commonly found in the environment but also in the gut of humans and animals. Although most strains of E. coli are harmless, others can cause illnesses like diarrhea, urinary tract infections, pneumonia, or worse. Some E. coli strains produce Shiga toxins. The toxins are named after Kiyoshi Shiga, who first described the bacterial origin of dysentery caused by Shigella dysenteriae. The most common sources for Shiga toxin are the bacteria S. dysenteriae and the Shigatoxigenic group of E. coli. Shiga toxin-producing E. coli or STEC can cause particularly serious disease or even death. The most commonly identified STEC belong to the serogroup O157:H7, but there are many other strains, sometimes called “non-O157 STEC”, like E. coli serogroups O26, O103, O104, O111 and other enterohemorrhagic E. coli (EHEC).
Symptoms of STEC infections?
People of any age can become infected. The symptoms of STEC infections vary for each person but often include severe stomach cramps, diarrhea (often bloody), and vomiting. If there is fever, it usually is not very high (less than 38.5˚C). Most people get better within 5–7 days. Some infections are very mild, but others are severe or even life-threatening. Around 5–10% of those who are diagnosed with STEC infection develop a potentially life-threatening complication known as hemolytic uremic syndrome (HUS). Very young children and the elderly are more likely to develop severe illness than others, but even healthy older children and young adults can become seriously ill.
Clues that a person is developing HUS include decreased frequency of urination, feeling very tired, and losing pink color in cheeks and inside the lower eyelids. Persons with HUS should be hospitalised because their kidneys may stop working and they may develop other serious problems. Most persons with HUS recover within a few weeks, but some suffer permanent damage or die.
The incubation period after ingesting the E. coli is usually 3-4 days after the exposure, but may be as short as 1 day or as long as 10 days. The symptoms often begin slowly with mild stomach pain or non-bloody diarrhea that worsens over several days. HUS, if it occurs, develops an average 7 days after the first symptoms, when the diarrhea is improving.
Where do STEC come from?
STEC live in the guts of ruminant animals, including cattle, goats, sheep, and deer. The major source for human illnesses is cattle or indirectly through cattle faeces contaminating growing plants and the environment. STEC that cause human illness generally do not make animals sick. Other kinds of animals, including pigs and birds, sometimes pick up STEC from the environment and may spread it. Exposures that result in illness include consumption of contaminated food like ground beef, unpasteurised (raw) milk, vegetables, water that has not been disinfected, contact with cattle, or contact with the faeces of infected people. Sometimes the contact is pretty obvious (working with cows at a dairy or changing diapers, for example), but sometimes it is not (like eating an undercooked hamburger or a contaminated piece of lettuce). People have been infected by swallowing lake water while swimming, touching the environment in petting zoos and other animal exhibits, and by eating food prepared by people who did not wash their hands well after using the toilet.
STEC typically disappear from the faeces by the time the illness is resolved, but may be shed for several weeks, even after symptoms go away. Young children tend to carry STEC longer than adults. A few people keep shedding these bacteria for several months. Good hand-washing is always a smart idea to protect yourself and others.
How can STEC infections be prevented?
- Wash your hands thoroughly after using the toilet or changing diapers and before preparing or eating food. Wash your hands after contact with animals or their environments (at farms, petting zoos and fairs).
- Cook meats thoroughly. Ground beef should be cooked to a temperature of at least 70˚C. It’s best to use a thermometer, as colour is not a very reliable indicator of “doneness.”
- Avoid raw milk, unpasteurised dairy products, and unpasteurised juices (like fresh apple cider).
- Prevent cross contamination in food preparation areas by thoroughly washing hands, counters, cutting boards, and utensils after they touch raw meat.