An infection of Escherichia coli, or E. coli, occurs when an individual's bloodstream is contaminated with a harmful strain of intestinal bacteria, KidsHealth states. The person may be exposed by consuming contaminated water or foods, such as undercooked ground beef and unpasteurized milk or juice.
E. coli is most often passed along during food handling processes, according to KidsHealth. For example, bacteria can spread in beef that is accidentally contaminated by cow feces, and failing to cook the meat properly prevents the germs from being killed. Vegetables, such as spinach and onions, can also be contaminated when grown in cow manure or washed in infected water. The bacteria can also be contracted by skin contact or ingested along with water in pools.
E. coli are naturally occurring bacteria present in the intestinal tracts of humans and animals, according to Mayo Clinic. Exposure to low-risk strains is often harmless to healthy adults and may cause no symptoms or mild diarrhea. High-risk strains, such as O157:H7, can trigger more severe symptoms, including abdominal pain, cramping, vomiting and bloody diarrhea. Elderly adults, young children and people with weakened immune systems are at risk of experiencing a dangerous form of kidney failure known as hemolytic uremic syndrome. Symptoms usually appear within four days of exposure, but the infection has no cure, so patients are advised to rest and increase fluid consumption while waiting for the toxins to pass out of the system.