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.

The tests that pinpointed the strain were conducted by the World Health Organisation’s reference laboratory in Denmark, ECDC told AFP.

Thursday’s communique confirmed the ECDC’s previous suspicions that one of the STEC group was responsible for the killer outbreak.

It said seven outbreak strains found in Germany and two in Denmark were of an “indistinguishable pattern.”

The agency reiterated that contaminated food “seems the most likely vehicle of infection” but stressed the source was still under investigation.

“There is currently no indication that raw milk or meat is associated with the outbreak,” the agency said, repeating what it had said in a previous statement.

In Geneva, WHO said Thursday that the strain of the lethal bacteria that has killed 18 people in Europe is “very rare” and had never been seen in an outbreak form before.

“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.

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.

“Most cases are from, or have a history of travel to the North of Germany (mainly Schleswig-Holstein, Lower Saxony, North-Rhine-Westphalia and Hamburg),” the ECDC said.

“Within the EU, Sweden, United Kingdom, the Netherlands, Denmark and Spain have reported cases of HUS, related to the ongoing outbreak.”

The ECDC statement was issued on the basis of data for 10 deaths and 499 cases of haemolytic uraemic syndrome (HUS), a condition unleashed by STEC that causes bloody diarrhoea and serious liver damage.

“Laboratory results indicate that STEC serogroup 0104:H4 (Stx2-positive, eae-negative, hly-negative, ESBL, aat, aggR, aap) is the causative agent,” it added.

HUS caused by infections by STEC 0104 types of E. coli usually occur in young children under five, the CDC observed.

But in the latest outbreak, the great majority of cases have been adults and two-thirds of them women.

Backing that finding, the Swedish Institute for Communicable Disease Control said 90 percent of the 46 cases found in Sweden so far were in people over the age of 40, and most of them involved people between 50 and 69 years of age.

No cases had been discovered in people under 20, it said.

The infection dose is “very low,” with the microbe taking between three to eight days to incubate, the ECDC said on its website.

“The typical presentation of infections with STEC is acute gastroenteritis, often accompanied with mild fever and sometimes vomiting. The typically bloody diarrhoea is in most cases mild and self-limiting and most people recover within five to seven days,” it said.

The scare has ignited suspicions of different produce, including the disproved theory Spanish cucumbers were to blame, and official warnings for consumers to avoid raw vegetables have hit European vegetable growers hard.

Amid the confusion, Russia said it would blacklist imports of fresh vegetables from EU countries and blasted food safety standards in the bloc.