The Centers for Disease Control and Prevention (CDC) estimates that 73,000 cases of Escherichia coli O157:H7 or E. coli occur every year in the United States. 2,100 people are hospitalized, and 61 people die as a direct result of E. coli infections and complications that can result from infections. Recently, the CDC estimates of E. coli infections declined 36%.

What is E. coli?

Although E. coli has been often in the news as a foodborne pathogen, the vast majority of E. coli strains are harmless, including those commonly used by scientists in genetics laboratories. E. coli is found in the family of bacteria named Enterobacteriaceae, which is informally referred to as the enteric bacteria. Other enteric bacteria are the Salmonella bacteria (also a very large family, with many different members), Klebsiella pneumoniae, and Shigella, which many researchers consider to be part of the E. coli family.

E. coli bacteria were discovered in the human colon in 1885 by German bacteriologist Theodor Escherich. Dr. Escherich also showed that certain strains of the bacteria were responsible for infant diarrhea and gastroenteritis - an important public health discovery. Although the bacteria were initially called Bacterium coli, the name was later changed to Escherichia coli to honor its discoverer.

Soon after its discovery, E. coli became a very popular lab organism because scientists could grow it quickly on both simple and complex mediums. E. coli can grow in air, using oxygen as a terminal electron acceptor (aerobically) or without air, by what is called fermentative metabolism (aerobically). The ability to grow both aerobically and anaerobically classifies the E. coli bacteria as a facultative anaerobe.

Where does E. coli O157:H7 come from?

E. coli O157:H7 bacteria is believed to mostly live in the intestines of cattle,1 but has also been found in the intestines of chickens, deer, sheep, and pigs. E. coli O157:H7 does not make the animals that carry it ill; the animals are merely the reservoir for the bacteria.

While the majority of foodborne illness outbreaks associated with E. coli O157:H7 have involved ground beef, such outbreaks have also involved unpasteurized apple and orange juice,2 unpasteurized milk, alfalfa sprouts, and water.3 An outbreak can also be caused by person-to-person transmission of the bacteria in homes and in settings like daycare centers, hospitals, and nursing homes. Proper hygiene and appropriate isolation can limit the risk of person-to-person transmission.

Meat typically becomes contaminated with E. coli O157:H7 during the slaughtering process, when the contents of the animal's intestine and feces are allowed to come into contact with the carcass. Unless the carcass is sanitized somehow, the E. coli bacteria are eventually mixed into the meat, as it is ground into hamburger. Because the bacteria is mixed into the meat during the grinding process, and not just on the surface, thorough cooking (greater than 160 degrees) is required to prevent E. coli O157:H7 poisoning when the ground beef is eaten by the consumer.

Contaminated meat looks and smells normal. Although the number of organisms required to cause an infection are not known, it is suspected to be very small.

Hemorrhagic colitis (See Hemolytic Uremic Syndrome Below) Hemorrhagic colitis, the first E. coli symptom, is characterized by the sudden onset of abdominal pain and severe cramps, followed within 24 hours by diarrhea. As the disease progresses, the diarrhea becomes watery and then may become grossly bloody - bloody to naked eye. E. coli symptoms sometimes include vomiting, but rarely fever. The incubation period for E. coli O157:H7 infection (i.e., the period from ingestion of the bacteria to the start of symptoms) is typically 3 to 9 days, although shorter and longer periods are not that unusual. An incubation period of less than 24 hours would be unusual, however.

In most infected individuals, the E. coli symptoms last about a week and resolve without any long term problems. Antibiotics do not improve the illness, and some medical researchers believe that these medications can increase the risk of complications.10 Therefore, apart from good supportive care, such as close attention to hydration and nutrition, there is no specific therapy to halt E. coli symptoms. However, the recent finding that toxin E. coli O157:H7 initially greatly speeds up blood coagulation may lead to medical therapies in the future that could forestall the most serious consequences.11 Most individuals recover within two weeks.

For Kids With a Type of E. Coli -- Just Say 'No' to Antibiotics

Children infected with E. coli O157:H7 -- a bug that can cause severe diarrhea, vomiting, and even death -- should not take antibiotics. According to a new study, the drugs given to fight the infection could actually bring on a potentially fatal complication involving the kidneys.

E. coli can be contracted "from all kinds of things including water, cider, and many different foods," says David Lewis, MD, who reviewed the study for WebMD. The disease can also be spread from person to person, he says. For example, inadequate hand washing after changing the diaper of a sick child can easily result in the bug's rapid spread through a day care center. Lewis is with the Lucile Packard Children's Hospital in Palo Alto, Calif., and Stanford University Medical Center.

According to researcher Craig S. Wong, MD, and colleagues at the University of Washington School of Medicine in Seattle, approximately 15% of those who contract the bug each year will develop hemolytic uremic syndrome, or HUS. It's a serious condition that can result in the need for blood transfusions or even kidney dialysis, in which a machine must do the work of the kidneys. If not fatal, HUS can still cause lingering medical problems.

Wong's team investigated various factors that could potentially increase a child's risk for developing HUS. They studied more than 70 young children sick with laboratory-confirmed E. coli O157:H7 infections. Of the 10 children who developed the complication, five had been given antibiotics.

When a child eats an undercooked hamburger or swallows pool water contaminated with E. coli, it's not really the bacteria that makes them sick. What's responsible for the bloody diarrhea, vomiting, and fever is actually a toxic waste product that the bacteria produce. But, says Lewis, contrary to what you'd expect, and as this study shows, killing the bugs with antibiotics is not the answer. Although it's not yet understood for sure, the antibiotic could cause the bugs to pump out more toxins or to burst open and spill all their toxins at once as they die.

Lewis tells WebMD that the debate over whether to give antibiotics to children with this type of E. coli infection has been raging for quite some time. "This study strongly suggests that it's a very bad idea," he says. "It probably won't help and it might be harmful." If your child suddenly develops bloody diarrhea, he says, "it's important to contact a physician immediately." Until a sample can be taken and tested for the presence of E. coli, "parents should basically sit tight."

Despite the natural impulse to do whatever they can to help their child feel better, Lewis urges parents to avoid a potentially fatal error. The majority of E. coli cases clear up without complication and without antibiotics, he says, and "one thing is for sure: parents should not give leftover antibiotics to a child with bloody diarrhea."

According to the CDC, an estimated 73,000 cases of E. coli infection, resulting in an average 61 deaths, occur in the U.S. each year. Lewis tells WebMD that the long-term focus of research is, and should be, on preventing the disease, starting with the elimination of the bacteria from our food and water supply. "At this point," he says, "we really can't do anything but treat the symptoms." If a child becomes infected, all doctors can do is watch to see if complications arise and then "support the child through it. For now, we really don't have anything definitive once it develops," so the best bet is prevention.

What are the more severe symptoms and long-term risks of E. coli O157:H7 infection?

Hemolytic Uremic Syndrome

Hemolytic Uremic Syndrome (HUS) is a severe, life-threatening complication of an E. coli O157:H7 bacterial infection. Although most people recover from the symptoms of E. coli O157:H7 infection, about 5-10% of infected individuals go on to develop (HUS). Hemolytic Uremic Syndrome was first described in 1955, and is now recognized as the most common cause of kidney failure in childhood. E. coli O157:H7 is responsible for over 90% of the cases of HUS that develop in North America. In fact, some researchers now believe that E. coli O157:H7 is the only cause of HUS in children. HUS is an extremely complex process that researchers are still trying to fully explain. The essence of the syndrome is described by its three central features: destruction of red blood cells (hemolytic anemia), destruction of platelets (those blood cells responsible for clotting, resulting in low platelet counts, or thrombocytopenia), and acute renal failure.

Thrombotic Thrombocytopenic Purpura