German authorities reported Tuesday three suspected deaths from a strain of the E. coli bacterium and warned more were likely because of a "scarily high" number of new infections.
"The number of serious cases in such a short time period is very unusual, and the age groups affected is also atypical," said the Robert Koch Institute (RKI), Germany's national disease control and prevention agency.
"The source of the outbreak has not yet been identified," RKI head Reinhard Burger said. "We have to say clearly that we have to expect more fatalities in view of the high number of cases."
The RKI said more than 80 cases of haemolytic uraemic syndrome (HUS) had been reported in the past two weeks, a life-threatening disease caused by infection with the enterohaemorrhagic E. coli (EHEC) strain.
In the northern state of Schleswig-Holstein alone, there were some 200 suspected cases of people suffering from bloody diarrhoea, while in Lower Saxony there were 96 and in Hamburg 42.
The Lower Saxony health ministry said an autopsy was being carried out on an 83-year-old woman who died Saturday after suffering for a week from bloody diarrhoea.
The woman was confirmed to have been infected with EHEC, but tests were being carried out to see if this caused her death, the ministry said in a statement.
Health authorities in the northern city of Bremen said a young woman who had been showing signs of EHEC infection died overnight Monday, although tests have yet to confirm the cause.
And in the northern state of Schleswig-Holstein, a woman aged more than 80 infected with EHEC died on Sunday following an operation. Authorities said the cause of death was as yet unknown.
RKI head Burger called the recent number of recorded cases "scarily high".
Normally in a year there are around 1,000 EHEC infections and some 60 cases of HUS, he said. There were two fatalities in 2010 and two in 2009.
Currently the majority of those affected are adults, in most cases women, whereas previous outbreaks had principally hit children, the RKI said.
In 2010, for example, there were some 65 cases of HUS, of which only six were aged 18 years or older.
Most cases so far are confined to northern Germany.
According to the World Health Organization, HUS is characterised by acute renal failure and blood problems, with a fatality rate of between three and five percent. It can also cause seizures, strokes and coma.
The RKI added that the source of the EHEC outbreak had not yet been identified and advised people to heat food and observe proper standards of hygiene.
E. coli is commonly found in the gut of humans and warm-blooded animals. Most strains of E. coli are harmless but some can cause severe foodborne disease.
It is transmitted to humans primarily through consumption of contaminated foods, such as raw or undercooked meat and unpasteurised milk.
Faecal contamination of water and other foods, as well as cross-contamination during food preparation with beef and other meat products, contaminated surfaces and kitchen utensils, will also lead to infection.
For more information on the disease, see the World Health Organisation website: www.who.int/mediacentre/factsheets/fs125/en/
Explore further: Estimates reveal low population immunity to new bird flu virus H7N9 in humans