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"We hope that the number of cases will go down but we fear that it will worsen," said Oliver Grieve, spokesman for the University Medical Center Schleswig-Holstein in north Germany, where many of those afflicted are being treated.
The source of the virulent strain of the bacteria is unknown, German authorities said on Monday ahead of a crisis meeting of federal and state officials in Berlin. Most of the deaths have been in northern Germany.
The E. coli pathogen has been identified on cucumbers imported from Spain but it is unclear if they were contaminated there, during transport, or in Germany.
There are 36 cases of suspected E. coli in Sweden, all linked to travel in northern Germany, authorities said. A small number of cases have been reported in Britain, Denmark, France and the Netherlands, all linked with travel to Germany.
Rare strain causes serious complications
The German government has identified the pathogen as a relatively rare strain of Shiga toxin-producing E. coli, or STEC. The virulent bug has caused many cases of hemolytic-uremic syndrome, or HUS, a potentially life-threatening complication of E. coli infection.
The European Center for Disease Prevention and Control said in a risk assessment that the HUS/STEC outbreak is the largest ever in the world of its kind.