Deadly E. Coli Outbreak Is New Strain: WHO Mutant form has never been seen before By Evann Gastaldo, Newser Staff Posted Jun 2, 2011 7:17 AM CDT 1 comment Comments Researchers take samples from a cucumber for a molecular biological test in Brno, Czech Republic, Wednesday, June 1, 2011. (AP Photo/Petr David Josek) (Newser) – The deadly outbreak of E. coli that has killed 18 in Europe so far is a new, never-before-seen strain of the bacteria, the World Health Organization said today. It looks to be a mutant strain formed by two different types of E. coli bacteria, which could be why the outbreak is so dangerous—possibly the deadliest in recent world history—and so large, sickening more than 1,500 people so far and leading to rare kidney complications in hundreds. The new strain has "various characteristics that make it more virulent and toxin-producing," a WHO expert tells the AP. There could be an "animal source," the expert says, meaning that bacteria from human and animal strains could have traded genes. The resulting new form of E. coli appears to be more dangerous than other types, and also behaves in odd ways—such as mainly striking adults, rather than children and the elderly as is typically seen. Women, in particular, have been hit hardest by this new strain. However, the expert notes that it is difficult to know the entire scope of the problem since people with milder cases probably aren't getting medical attention. Click for more on the outbreak.