The E. coli bacteria that killed dozens of 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, scientists there are reporting. 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