Where does E. coli come from and How does E. coli bacteria spread?

More common than C. botulinum, and perhaps as notorious, is the bacterium Escherichia coli.

There are hundreds of different serotypes of this gram-negative bacterium, any one of which can cause disease, and many of them are part of the normal bacterial fauna of the intestines.

They can get into other parts of the body and cause trouble, 75 percent of urinary tract infections, for example, are caused by E. coli that got into the wrong place. Appendicitis almost always involves infection with a strain of E. coli, among other organisms.

In 1982, researchers discovered a serotype called O157:H7 that when ingested releases a toxin that causes direct damage to the mucosal wall of the large intestine. This can result in some real unpleasantness, including severe abdominal cramps and bloody diarrhea that lasts for a week or more, and that’s in the mild cases.

About 5 percent of cases have life-threatening complications. One is called hemolytic-uremic syndrome (HUS), which consists of destruction of red blood cells (hemolytic anemia), a reduction in blood platelets (thrombocytopenia), and kidney failure, allowing waste products to accumulate in the blood instead of being excreted in the urine. Another is thrombotic thromobocytopenic purpura (TTP), which includes all of the above symptoms plus fever and neurologic problems. These complications occur most frequently in children under 5 and adults over 60.

When E. coli makes the news, it’s usually because of an outbreak caused by eating or drinking something in a public place. That’s what happened on September 3, 1999. Ten children in counties near Albany, New York, were hospitalized with bloody diarrhea, and everyone wanted to know why. Health officials quickly discovered two facts: they were all infected with E. coli O157:H7 and they had all attended the Washington County Fair, held two weeks earlier.

By September 15, more than 900 fair attendees had reported diarrhea, and stool cultures found that 116 of them were infected with E. coli O157:H7. Sixty-five people were hospitalized, and eleven children had developed HUS. Two people, a 3-year-old girl and a 79-year-old man, both of whom had HUS, died. Finally, an environmental study of the fairgrounds uncovered the truth: one area at the fair where several food vendors used water to make drinks and ice was supplied by a well. The well water was highly polluted with E. coli, and careful testing showed that the strain was O157:H7.

But the cases that don’t make the newspapers, the ones that occur in homes, are actually more numerous. The kitchen is a fine place to pick up this bacteria because the main reservoir of the germ is in food, usually in cattle. The germ lurks in undercooked hamburger meat and unpasteurized milk, and since cattle carry the germs without having any symptoms of disease, you can’t easily tell which cattle are infected.

Because the germ is shed in human stool, you can pick it up by that route, too. You wouldn’t think that ingestion of other people’s stool would be a frequent occurrence, but when someone forgets to wash his hands after using the toilet and then handles food that you eat, that’s exactly what can happen. Babies’ diapers are a good place to find E. coli, too as well as other nasty things.

In 1997, the CDC did an epidemiological study to figure out where you were most likely to get E. coli O157:H7 infection, and found that most infections could be traced to living on or visiting a farm, eating undercooked hamburger meat, or obtaining beef from private slaughtering sources rather than in a conventional store. Contrary to what you might believe from what you read in the papers and hear on TV, eating in a table-service restaurant is a greater infection risk than eating in a restaurant that is part of a major fast-food chain. Maybe this is because the fancier the restaurant, the more they touch your food with their hands, but as far as we know no one has proven this to be the case.

Between 1993 and 1997, 3,260 cases of E. coli infection were reported to the CDC, and 8 of them were fatal. As with many infectious diseases, the very young, the very old, and the immunocompromised are most at risk. Normally, healthy people don’t die from this infection, and the only treatment for most uncomplicated cases is supportive, that is, you go on a bland diet and drink plenty of fluids. Antibiotics have little effect, either on the illness itself or in limiting the serious complications. If HUS or TTP is involved, the treatment is quite complicated and includes kidney dialysis, plasmapheresis (withdrawing blood, separating the plasma, and then returning the blood cells to the patient), and other therapies.

There is another interesting characteristic of E. coli O157:H7: it is more common in some geographic areas than in others. O157:H7 infections occur in the United States as a whole at a rate of about 2.9 per 100,000 population per year. But in Georgia the rate is 0.6 per 100,000 and in Minnesota it is 5.5, almost 10 times as common. No one is certain, but differences from region to region in the number of direct farm exposures and the consumption of locally processed beef may contribute to this variation. When it comes to E. coli exposure, cities are probably safer than rural areas. There is considerable seasonal variation in the occurrence of infection as well, most infections occur during the summer.

O157:H7 is not the only serotype that produces toxin and causes serious illness. In Helena, Montana, in 1994, someone came down with an infection of a serotype called O104:H21, which had all the familiar symptoms of its more famous cousin. Eventually, ten other residents of or visitors to Helena were found to have the same germ. In this outbreak, most of the people affected had consumed milk and milk products from a certain dairy. When they tested the pipes and other equipment used to transport pasteurized milk at the dairy’s plant, they found high levels of fecal coliforms, but none of E. coli O104:H21, so the source of the outbreak remains uncertain.

Apple cider is often locally produced in small mills and sold unpasteurized. Many people believe it tastes best this way. But there can be problems with it. In 1996, there were three outbreaks of O157:H7, each associated with a different brand of unpasteurized apple cider. In the largest outbreak, 66 people got sick and one died. Using “drop apples”, that is, apples that have fallen to the ground, is common in cider making. But such apples can become contaminated with manure from infected cattle, which may be what happened in this case.

Anyone who gets bloody diarrhea should have a stool specimen cultured, it’s the only way to know if O157:H7 is the culprit. Although aggressive treatment is required for HUS and TTP, there’s very little you can do about an uncomplicated infection from O157:H7. Antibiotics are not only ineffective, but can actually lead to kidney complications. Even antidiarrheal agents such as Imodium, Pepto-Bismol, or Kaopectate should be avoided, because they make things worse. Most people simply recover within a week or 10 days. That leaves prevention as the only alternative.

Cooking food well almost always eliminates the threat of infection from E. coli, it is rendered harmless at temperatures above about 160°F. If you want to be absolutely sure your food got that hot, you have to test it with a meat thermometer. Pasteurization also makes the germ harmless, so if you never eat pink beef and drink only pasteurized beverages, you can be pretty certain E. coli won’t harm you. But if you, or those who prepare your food, don’t wash their hands before leaving the bathroom, you’re taking your chances.

Ground beef can still be contaminated after it’s cooked, and milk products can be contaminated after pasteurization. This means you shouldn’t put cooked hamburgers on the same unwashed plate that held them when they were raw. Anything that touched raw meat, counters, utensils, a meat thermometer, plates, your hands, should be washed with hot soapy water before they touch anything else.

You should also keep refrigerated meat separate from other foods.