How to Outsmart Dangerous E. Coli Strain

Article excerpt

Scientists have recently identified a rare but dangerous type of the Escherichia coli bacterium. Most E. coli are harmless inhabitants of the intestinal tract, but this variant, called E. coli O157:H7, produces toxins in the human gut that are capable of deadly damage.

On Jan. 13, 1993, a physician in Washington state reported a cluster of children with hemolytic uremic syndrome (HUS), the major cause of acute kidney failure in children in this country. There was also an increase in emergency room visits for bloody diarrhea in people of all ages.

Laboratory tests from the stools of infected patients showed E. coli O157:H7. Most infected people had eaten hamburgers from local restaurants of Jack-in-the-Box, a nationwide fast food chain.

Health officials investigated the illness reports and traced the meat in the hamburger patties to one processing plant but were not able to determine the source of the meat. Investigators also discovered that the patties had been undercooked at the restaurant. Thorough cooking would have killed the bacteria, but live, they were free to do their damage.

Reports of illness continued to mount and by the end of February, three children in Washington state and one other in California had died of HUS complications. More than 500 people from Washington, Idaho, California, and Nevada had laboratory-confirmed E. coli O157:H7 infections. Of those, more than 50 people had been infected by person-to-person contact with someone who had eaten the contaminated hamburgers.

As news of the outbreak spread, reports of previous food-borne illnesses involving E. coli O157:H7 were collected and reviewed. One outbreak in 1991, caused by contaminated fresh-pressed, unpreserved apple cider from a southeastern Massachusetts mill, had resulted in the hospitalization of four children with HUS. Another 17 children required medical treatment (see "How Did It Get in Apple Cider?").

Before the Massachusetts mill incident, it was not common knowledge that this strain of E. coli could survive the acid environment of apple cider. Scientists from the national Centers for Disease Control and Prevention and from the University of Georgia continued to study the cider mill outbreak, and published a number of reports in professional journals.

Then, last July and August, several months after the ground beef outbreak in the northwestern states, people who had eaten at two Oregon restaurants of another nationwide chain became ill with confirmed E. coli O157:H7 infections. At press time, public health officials, including Food and Drug Administration scientists, were trying to identify the food source of the contamination.

Bug Not Always Bad

Not all E. coli are harmful. E. coli is one of several bacterial types that are normal to the human gut and pass through the intestinal tract with feces. It has been known for many years that in healthy people, this group of bacteria and other normal microbial flora reduce the chance of pathogens--harmful bacteria that enter the body through food and water--from colonizing in the intestines and possibly causing illness.

E. coli is also helpful outside the body. In food laboratories, scientists use E. coli as an indicator of contamination, explains microbiologist Peter Feng, Ph.D., of FDA's Center for Food Safety and Applied Nutrition (CFSAN). If E. coli can be isolated from the suspect food, it implies that the food is contaminated by fecal matter, he says.

Research scientists also put the bug to good use in DNA studies (see "When E. coli Is Helpful").

"It's because of the knowledge that E. coli is a normal intestinal inhabitant that studies of potentially harmful strains were delayed," says CFSAN microbiologist Joseph Madden, Ph.D. "We now know of at least six types of E. coli, including O157:H7, that are particularly virulent and can cause serious illness."

CDC first isolated E. …