Killer germ: First outbreak of 'rare' microbe: - WHO

A lethal bacteria that has killed 18 people in Europe is "very rare" and had never been seen in an outbreak form before, the World Health Organisation (WHO) said on Thursday.

"This strain isolated from cases in the infection outbreak in Germany has never been seen in an outbreak before," Gregory Hartl, the WHO spokesman, said.

"It has been seen in sporadic cases and is very rare," he added.

The European Union's watchdog for disease prevention said Thursday that lab tests had identified the strain of a lethal E. coli germ that had caused an amplifying food scare.

In a statement, the European Centre for Disease Prevention and Control (ECDC) said the "causative agent" was a member of a group of bacterial strains called Shiga toxin-producing Escherichia coli, or STEC.

Eighteen people have been killed in Europe -- 17 of them in Germany and one in Sweden -- and more than 2,000 have fallen sick from the bug since Germany first sounded the alarm on May 22, according to a toll compiled by AFP on Thursday from national health authorities.

Roughly two thirds of confirmed cases have been found in women and the bacteria has not yet been detected in anyone under younger than 20 years.

Health officials have so far failed to pinpoint the origin of the outbreak.

Initial speculation that cucumbers from Spain were the culprit has been discarded and Spain on Thursday demanded a payback for its farmers.

Farmers across Europe face have been dealt a death blow amid official warnings that to avoid raw vegetables.

Britain reported seven cases of the mysterious lethal bacteria on Thursday, including three people who had recently travelled to Germany and four German nationals.

Russia meanwhile blacklisted vegetable imports from Europe in a moved slammed as "disproportionate" by the European Commission.