Health authorities in Germany have achieved a breakthrough in their search for the origin of the deadly E coli epidemic that killed 31 people to contaminated bean sprouts.

Laboratory tests of bean sprouts left over by two women in a family near Bonn, who fell ill after consuming the vegetable, showed that it was tainted with the highly virulent strain, which causes the life-threatening haemolytic uramic syndrome (HUS).

The package of bean sprouts taken from the waste bin of the family was traced to the farm in Uelzen, in the state of Lower Saxony, which has been already under investigation for more than a week as a potential source of the outbreak.

Johannes Rummel, the NRW Minister for consumer affairs, said for the first time since the outbreak of the deadly infection over a month ago, investigators succeeded in establishing scientifically a link between the farm and bean sprouts contaminated with the bacteria.

When the mother and daughter in a family developed symptoms of E coli infection after eating bean sprouts in mid-May, the father took the left-over package of the vegetable from the waste bin and handed over to the health authorities.

Laboratory tests confirmed that it was contaminated with the lethal bacteria, which has so far claimed 31 lives and infected more than 2,000 people, 722 of them with HUS.

The two women are in a very acute condition and therefore they cannot be questioned about where they bought the bean sprouts package, Rummel said.

The father, who did not eat the vegetable, has so far developed no symptoms of E coli infection, he said.

The discovery of the E coli-tainted bean sprouts “confirms out current warnings” against consuming the vegetable, the Minister said.

The farm in Uelzen came under the suspicion of health officials after they discovered that its supply routes were linked to all main centres of E coli outbreak in northern Germany, the epicentre of the epidemic.

However, tests of nearly a hundred bean sprouts samples taken from the farm so far have been negative, according to the health Ministry in Lower Saxony.

Earlier, the Robert Koch Institute, Germanys national disease prevention and control centre, announced that investigators have narrowed down their search for the source of the killer bacteria to bean sprouts, even though they did not have any scientific evidence.

The Robert Koch Institute and the Federal Institute for Risk Assessment lifted their warnings against cucumbers, tomatoes and lettuce as potential carriers of the bacteria and said those vegetables can be consumed without any apprehension.

Even though the farm in Uelzen was suspected of being a source of the worst E coli outbreak in Germany for more than 60 years, this was the first time a link between bean sprouts tainted with the bacteria and the farm was scientifically proved.