German hospitals are struggling to cope with the flood of E.coli victims, health minister Daniel Bahr said on Sunday, as scientists remain puzzled by the deadly bug.

E. coli has already killed 19 and infected 1,700 people across Europe.

Hospitals in the northern port of Hamburg, epicentre of the outbreak that began three weeks ago, have been moving out patients with less serious illnesses to handle the surge of people stricken by a rare, highly toxic strain of the bacteria.

'We're facing a tense situation with patient care,' Bahr told the Bild am Sonntag newspaper on Sunday. He added hospitals outside Hamburg could be used to make up for 'insufficient capacity' in Germany's second largest city.

Authorities in Germany are racing to track down the source of the pathogen, which has infected people in 12 countries - all of whom had been travelling in northern Germany.

Officials believe people were made ill by eating lettuce, tomatoes, cucumbers or other raw salad vegetables in Germany.

Scientists suspect the source of the contamination may have been poor hygiene at a farm, in transit, or in a shop or food outlet.

Many of those infected have developed haemolytic uraemic syndrome (HUS), a potentially deadly complication attacking the kidneys.

The rare strain of E.coli has the ability to stick to intestinal walls where it pumps out toxins, sometimes causing severe bloody diarrhoea and kidney problems.

Some patients have needed intensive care, including dialysis. It has hit women more than men, and most of those who have died were elderly.

A spokesman for the Regio Clinics, the largest private hospital in the state of Schleswig-Holstein that surrounds Hamburg, said the crisis was straining resources.

'All the hospitals in the region are pushing their limits,' said the spokesman. 'We can handle it but some of our patients have to be sent to other hospitals, especially those with HUS or needing dialysis.'

He added: 'Operations for non-life-threatening illnesses are being rescheduled. It looks like the situation may be improving though, as we now have only 60 patients who need to be isolated, compared with 109 on Friday.'

People were steering clear of salads. 'I'm a vegetarian, so it hits me especially hard,' said taxi driver Wolfgang Roenisch. 'I've stopped eating cucumbers, tomatoes and salad.'

But Amin Najibi, owner of a small restaurant, said there were still fearless salad-eaters: 'We're still serving salad though demand has fallen a bit. I think people are eating normally.'

Scientists are pursuing a number of theories as to where the deadly strain of E.coli originated. Experts told Welt am Sonntag newspaper it could have spread from a biogas plant. During the biogas fermentation process new bacteria often develop. 'They cross and fuse together,' Bern Schottdorf said.

'What then happens has so far not been researched.' On Saturday a microbiologist said officials had identified a restaurant in the northern port city of Luebeck as a possible place where the bug had been passed to humans. At least 17 people infected with E.coli had eaten there.-Reuters