E. coli and E. coli 0157

Posted by Judy Arbique Sep 20, 2006

Before I give an update on the E. coli 0157 spinach outbreak in the U.S., I thought it might be useful to have a general discussion on Escherichia coli (E. coli). The media often refers to foodborne disease caused by E. coli 0157 simply as E. coli outbreaks. which is misleading because people then associate E. coli with illness, infection and disease.

In fact, most E. coli are non-pathogenic (non-disease-producing) and are referred to as commensal - the dictionary definition of commensal is "one who eats at the same table".

E. coli is one of the many bacteria that form part of the normal veneer of bacteria that inhabit the human bowel - to each his own! These commensal bacteria are helpful, not only in digesting and breaking down food, but also in protecting against harmful organisms which may be introduced to the gastrointestinal tract through food and water. A healthy bacterial bowel population provides competition for pathogenic organisms that might be ingested, and protects against colonization by them.

That isn't to say that bacteria in this group do not ever cause infection - some commensal bacteria can cause infection if host defenses are compromised. E. coli is sometimes a cause of surgical/wound infections and septicemia, post-surgery, and is the most common cause of urinary tract infection in women. Irritations to the urethra may allow E. coli, which commonly contaminate the perineum (region between the anus and genital organs), to attach to cells in the urethra and bladder and cause infection - anyone who has had a urinary tract infection will certainly remember how painful this can be.

Some types of E. coli have virulence factors (the ability of an organism to cause disease). There are a number of virulence factors that differentiate 'garden-variety' commensal E. coli from pathogenic stains associated with gastroenteritis from food or water. E. coli 0157 is a virulent strain of E. coli that is pathogenic to humans. E. coli 0157 is common in cattle, sheep and other farm animals and is not associated with disease. However, the same cannot be said for humans where the infectious dose for some strains of E. coli 0157 can be as low as 10-100 organisms. If animal feces, or material contaminated with animal feces, gains access to crops or water supplies that do not have adequate treatment, illness in humans is expected.

Waterborne outbreaks are uncommon in North America; however, they do occur. The most recent North American waterborne E. coli 0157 outbreak happened in the town of Walkerton, Ontario in May 2000. At that time Walkerton had a population of 5000, and 1286 people became infected - 65 of whom were hospitalized and 6 who died. The outbreak was associated with manure run-off into the water system, and subsequent inadequate treatment of the water, which if I remember correctly was related to a malfunction in the treatment plant. A previous waterborne outbreak associated with contaminated well-water, occurred in August 1999 at the Washington County Fair in New York State when at least 1000 people became ill - 2 of whom died.

E. coli 0157 foodborne disease is much more common than waterborne disease in North America. Because the organism may be found normally in the bowels of farm animals, they can contaminate the carcass and meat during slaughter and processing, leading to gastrointestinal infection when the meat is not thoroughly cooked - beware of the rare hamburger!

Additionally, crops, such as spinach, can become contaminated from manure run-off in the soil. The bacteria, once deposited on the leaves of produce, are difficult to remove by washing, which is the case with the current E. coli 0157 outbreak in the U.S. involving fresh bagged spinach. As of September 19, 2006, the total number of reported cases was 131 and 2 new States - Illinois (1) and Nebraska (6) have been added to the list of those involved CDC Update.