German E. coli outbreak - Deadly E. coli is New Strain of Bacteria, Source Still Unknown

The lethal E. coli bacteria that has left 18 dead and more than 1,500 sick in Europe is a new strain that experts have never seen before, the World Health Organization announced Thursday.

Early investigations suggest that the strain is an altered type of two E. coli bacteria with deadly genes that, experts said, could explain the widespread and dangerous nature of the illness.

"This is a unique strain that has never been isolated from patients before," Hilde Kruse, a food safety expert at the WHO, told The Associated Press. "[It has] various characteristics that make it more virulent and toxin-producing."

The source of the bacteria remains unknown, continuing to baffle experts.

The strain has hit eight countries in Europe, but has been concentrated in Germany.