The death toll has risen to 35 in Germany's E. coli epidemic and health officials say about 100 patients have severe kidney damage.
The source of infection has been identified as bean sprouts from an organic farm in northern Germany.
At least 3,255 people have fallen ill, mostly in Germany, of whom at least 812 have a complication that can be fatal.
About 100 patients with damaged kidneys will need transplants or life-long dialysis, one health expert said.
Karl Lauterbach, an epidemiologist who is also an opposition Social Democrat (SPD) politician, warned that E. coli infections were growing worldwide.
Since the start of the outbreak in May, all but one of the deaths have been in Germany.
Investigators say they believe organic bean sprouts from a farm in Bienenbuettel, Lower Saxony, were responsible. The farm's produce has been withdrawn from sale.
Several workers from the farm have fallen ill with the virulent new E. coli strain.
Germany's national disease agency, the Robert Koch Institute (RKI), said the death toll rose to 35 at the weekend, but the rate of new infections was declining.
Yet it is still not clear how the bean sprouts became contaminated with the bug, which normally lives in the guts of cattle and sheep.
Health experts quoted by the Associated Press news agency said the toxin produced by the new E. coli bug in Germany was especially potent.
The German strain causes not only bloody diarrhoea but also neurological disorders, including paralysis in some cases. The potentially fatal complication is called haemolytic uraemic syndrome (HUS).
Tests show that the strain has genes that make it resistant to many antibiotics.
Germany plans to tighten its checks on fresh vegetables and there are calls to speed up lab reporting procedures.
Consumer Affairs Minister Ilse Aigner said she had asked regional authorities across Germany to prioritise checks on growers and importers of bean sprouts, including handlers of imported seeds.
Germany has lifted its warning against eating raw cucumbers, tomatoes and lettuce, but kept it in place for the sprouts.
The European Commission has offered 210m euros (£186m; $303m) to European farmers who have seen a dramatic loss of income since the outbreak started in early May.
Initially Germany mistakenly blamed Spanish cucumbers - a move which brought some Spanish vegetable exporters to a standstill.