Science Scope

Why is it so hard to pinpoint the cause of E. coli?

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First, they thought it was cucumbers. Then, sprouts. Why can't German health authorities figure out what is causing the deadliest outbreak of E. coli in recent history?

It's not easy to remember the ingredients of everything you've eaten in the last few weeks.

As German health authorities try to determine the source of a deadly E. coli outbreak in Germany, they are bumping up against this basic obstacle as they try to figure out what food could have been contaminated with the bacteria that has infected 2,200 people and killed 22 in the last month.

At first, they thought it might be Spanish cucumbers because 80% of the infected remembered eating cucumbers, which, in Europe, are often grown in Spain. Now, they're investigating sprouts grown in Germany (so far with negative results). If the tests continue to come back negative, they'll have to come up with a new hypothesis.

Meanwhile, farms, restaurants and food processing facilities are scrubbing away all germs -- so even if investigators find the place that was the source of the outbreak, all the tests will come back negative.

As The New York Times reports,

“Even if all the samples are negative, maybe you just missed it,” Dr. Tauxe said. “You can go to a place reeking of chlorine, and find nothing.”

The difficulty of finding the cause has to do both with the complexities of a global food supply chain as well as the challenge of establishing and maintaining a system that can determine when a number of individual cases constitutes an outbreak.

The World Health Organization's Dr. Flemming Scheutz said that the German health system, which is decentralized, did not see the full scope of the outbreak until people were hospitalized. (The U.S. has a national system for reporting such cases.)

The New York Times underscores the challenge of pinpointing the cause of an E. coli outbreak:

Indeed the largest serious outbreak of E. coli, which sickened more than 8,000 people in Japan in 1996 has been widely attributed to eating contaminated radish sprouts, but scientists were never able to prove contamination in the laboratory.

How E. coli causes illness

E. coli (full name Escherichia coli) is a bacteria naturally found in the intestines of cattle, humans, poultry and other animals.

When animals are slaughtered, the bacteria will contaminate the surface of meat. They are spread further when the meat is processed or ground. Incorrectly composted manure and tainted water can contaminate raw fruits and vegetables. People also spread the bacteria in food handling and preparation unless they regularly wash their hands.

PBS NewsHour, quoting William Marler, a foodborne illness attorney, reports that 50 bacterium of e. coli can kill you. And 100,000 of them can fit on the head of a pin.

If the bacteria enter the body and make it past acids in the stomach, they can multiply in the intestines and eat away at the intestinal wall, causing bloody diarrhea and cramping. The strain of E. coli causing the current outbreak is also causing a high rate of hemolytic uremic syndrome (HUS), a sometimes-deadly complication linked to kidney failure.

PBS NewsHour quotes Caroline Smith De Waal of the Center for Science in the Public Interest:

"The kidneys are particularly vulnerable as they try to eliminate the toxin from the blood and can become overwhelmed."

Unique characteristics of this strain

This particular outbreak of E. coli is caused by the rare strain O104. E. coli infections typically give rise to HUS in 5% to 10% of cases, but this time, the rate is an unprecedented 36%.

Other unusual characteristics of this outbreak are its disproportionate effect on women and people in the prime of their lives. E. coli usually hits children and seniors more than the rest of the population. One conjecture is that the source of the outbreak is a common ingredient in salad, which investigators believe women eat more often than men do.

For now, while investigators attempt to track down a bacteria that may be long gone, they are cautioning Germans against eating tomatoes and lettuce.

Photo: julie@organikal

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Laura Shin

Features Editor

Laura Shin has been published in The New York Times, The Wall Street Journal and The Los Angeles Times, and is currently a contributor at Forbes. Previously, she worked at Newsweek, the New York Times, Wall Street Journal and LearnVest. She holds degrees from Stanford University and Columbia University's Graduate School of Journalism. Follow her on Twitter. Disclosure