Gina Kolata of The New York Times writes in tomorrow’s paper that the E. coli O104 that killed 40 people in Germany over the past month have a highly unusual combination of two traits and that may be what made the outbreak among the deadliest in recent history.

One trait was a toxin, called Shiga, that causes severe illness, including bloody diarrhea and, in some patients, kidney failure. The other is the ability of this strain to gather on the surface of an intestinal wall in a dense pattern that looks like a stack of bricks, possibly enhancing the bacteria’s ability to pump the toxin into the body.

With the two traits combined in one strain of E. coli bacteria, “now they are highly virulent,” said Dr. Matthew K. Waldor, an infectious-disease expert at Harvard Medical School who was not connected with the new research.

The new findings, by a team led by Helge Karch of the University of Münster, are being published Wednesday in the journal Lancet Infectious Diseases. They result from two days of fevered work to characterize the bacteria causing the illness that raced through Germany in May.

Experts in the United States praised the German scientists’ work. The work and the entire outbreak are “a real game-changer,” said Dr. Philip I. Tarr, a professor of pediatrics and expert in gut infections at Washington University School of Medicine in St. Louis. John Mekalanos of Harvard called the paper “extremely important.”

Dr. Karch, a well-known expert in E. coli, infections, got the first stool samples on May 25. Over the next few days, more and more samples flooded his lab, 50 to 100 a day. “You can’t imagine,” he said.

He isolated the strain that was causing the illness and analyzed it to determine that it was strain O104:H4. Then he began investigating the bacteria’s DNA. First he determined what kind of Shiga toxin it made. Then he did adherence tests and found that the bacteria stuck to surfaces in the bricklike pattern. It is an unmistakable phenomenon: “Once you see it you will never forget it,” Dr. Karch said.
He posted the results and provided detailed information so most labs that had a suspicious stool sample could analyze it immediately and see if the stool contained O104:H4 bacteria. Until he posted that information, most labs would be at a loss. The strain is so rare that there are no standard tests to find it.

Dr. Karch also realized that the O104:H4 strain had been seen before in bloody diarrhea and kidney failure, but only on rare occasions — first in Germany in 2001, then sporadically in a few other countries. And in each outbreak, at most a few people were ill.

Dr. Karch thinks it smoldered in human populations, causing mild illnesses in most and occasionally causing severe disease. Then, somehow, it was passed to the bean sprouts by someone who harbored the bacteria. And since sprouts are eaten raw, they were highly infectious.

He himself does not like sprouts, he says, though his wife does. Aware that sprouts have always been “a high-risk food” for bacterial illnesses, he will not touch them unless they have been cooked.