The E. coli that killed dozens and infected thousands of people in Germany last month has a "highly unusual" combination of traits that made it particularly deadly, reports The New York Times' Gina Kolata. Researchers say that one trait was the toxin Shiga — which causes severe illness and kidney failure in some patients — and the other is the bacteria's ability to stack itself in a brick-like pattern on the intestinal wall, possibly to more efficiently pump toxins into the body, Kolata says. "The thought is that the bacteria started out being able to aggregate with the brick pattern and then were infected with a bacterial virus that gave them the Shiga toxin," she adds. According to a new paper published in Lancet Infectious Diseases by researchers at the University of Münster, the two traits combined made the bacteria more virulent than most other strains. The strain is so rate that patients had no immunity against it, the researchers tell Kolata.