Fighting back against food poisoning E. coli: Outbreaks of the kind that have taken place in America and Japan can be prevented.

August 04, 1996|By James B. Kaper and James P. Nataro

SO FAR, the outbreak of food poisoning in Japan has struck more than 10,000 people, killing seven and hospitalizing some 600 others. In 1993, more than 700 Americans became ill after consuming under-cooked meat from a hamburger chain.

The culprit in both outbreaks was a bacterial species of Escherichia coli, or E. coli. And similar outbreaks are preventable if consumers are cautious about food preparation. E. coli strains are almost universally present in human intestines and most are harmless micro-organisms that serve important functions in nutrition and normal gastrointestinal health.

Some E. coli bacteria, however, have acquired genes that allow them to capitalize on their intestinal niche, wreaking havoc on their hosts.

One type of E. coli, "enterotoxigenic E. coli" (ETEC), strikes travelers visiting developing countries, and is known by such colorful names as Montezuma's Revenge, Delhi Belly and Dhaka Drip.

Such infections can cause three to five days of watery diarrhea, which may be quite severe and debilitating. Fortunately, this illness generally clears up on its own, leaving little more than a vacationer's anecdote.

But the type of E. coli that has put this species on the front page is termed enterohemorrhagic E. coli (EHEC), and the most notorious EHEC strain is E. coli O157:H7.

This strain was first isolated in 1982 by U.S. researchers after an outbreak, and has been labeled an emerging pathogen along with Cryptosporidium, Hantavirus, and HIV.

In contrast to the watery traveler's diarrhea, E. coli O157:H7 can cause bloody diarrhea, intestinal inflammation, intestinal necrosis and a severe kidney affliction called hemolytic uremic syndrome (HUS) that can result in kidney failure and death. It affects mostly children and the elderly.

These severe complications are caused by a potent toxin called Shiga toxin, which is released by the E. coli O157:H7 and is absorbed into the bloodstream and ultimately the kidneys.

Death sometimes occurs during an acute phase of the illness from central nervous system or gastrointestinal problems. Ten percent of HUS cases result in kidney failure that ends in death. Some patients are left with permanent renal failure, which may require a kidney transplant. But in most cases, kidney damage takes care of itself spontaneously, requiring only temporary use of a dialysis system.

There is no cure for HUS; antibiotics do not stop the organism in humans. Indeed, recent research suggests that some antibiotics may make the disease worse because they cause the dying bacteria to release even more toxin.

An experimental therapy now being evaluated in Canada uses a chemical to soak up the toxin in the bloodstream, but these trials are preliminary.

Overall, the death rate from EHEC infection is probably less than 1 percent, but in outbreaks involving hundreds and thousands of individuals, the number of deaths and permanently impaired survivors can become horrifying.

How does one become infected with E. coli O157:H7?

This deadly bacterium can be found in the intestines of about 1 percent of healthy cattle. If feces harboring the organism contaminate the meat, the stage is set for infection.

Modern food processing technology can encourage the spread of this organism because meat from hundreds of farms is combined in a single processing plant. Hamburger from a single plant is then distributed to hundreds of stores and restaurants.

Even if the E. coli O157:H7 were present in only one cow on a family farm, the processing system provides tremendous opportunity for distribution of the organism to several states.

Hamburger is not the only source of infection: Other outbreaks have been traced to roast beef, raw milk, salami, vegetables and apple cider. Infection has also been transmitted via an unchlorinated municipal water supply, from swimming in a contaminated lake and directly from person to person.

E. coli O157:H7 is notable for the very low dose needed; as few as 10 to 100 organisms can cause disease. In contrast, several million enterotoxigenic E. coli are needed to cause traveler's diarrhea. This low infectious dose makes it particularly easy for transmission in day-care settings, where even an apparently healthy child can still excrete E. coli O157:H7.

The source of the outbreak in Japan is unknown, but officials there have reason to believe that many smaller outbreaks involving different routes of transmission contributed to the nationwide outbreak.

In response to the 1993 outbreak in the United States, the federal government has recently taken steps to improve meat inspection. Amazingly, in this era of gene therapy and numerous medical wonders, meat inspection has changed little since the beginning of the century. Under the fancy name "organoleptic" the method really consisted of seeing, touching, and smelling the meat.

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