The World Health Organization is warning people not to take antibiotics if they get sick in the E. coli outbreak that began in Germany last month.
Anti-diarrhea medication isn't recommended either, as it stops the bacteria from quickly leaving the body, the United Nations health agency said.
WHO epidemiologist Andrea Ellis said use of either treatment "can actually make the situation worse." That's because killing toxin-producing bacteria, such as the ones responsible for this outbreak, can actually cause them to release more toxins.
But Ellis told reporters in Geneva on Friday that doctors treating infected patients can prescribe antibiotics in specific cases.
The outbreak caused by a very rare strain of E. coli bacteria is still resulting in new illnesses as the search for the source continues.
German health officials recorded 199 new cases in the past two days. That brought the total of those infected in the last month to more than 1,700 in Germany alone.
The WHO said that as of May 31, nine other European nations have reported a total of 80 people sick, most of whom had recently visited northern Germany.
"All these cases except two are in people who reside in or had recently visited northern Germany during the incubation period for the infection -- typically 3 to 4 days post-exposure -- or in one case, had contact with a visitor from northern Germany," the WHO said in a statement.
In all, 18 people have died, making it the deadliest ever E. coli outbreak. It's also the third-largest, well behind the 1996 Japanese outbreak that sickened more than 9,000.
Among the ill are 520 who are suffering from a life-threatening complication called HUS (hemolytic uremic syndrome), which can cause kidney failure or death.
The German government decided on Friday to set up a national task force to hunt down the source of the outbreak, which remains a mystery.
While suspicion has fallen on raw tomatoes, cucumbers and lettuce as the source of the germ, researchers have been unable to pinpoint the cause.
The investigation so far has found that people who have fallen ill have reported they had a tendency to eat more raw tomatoes, cucumbers and lettuce. But it was not clear if any of these foods are actually the source.
The World Health Organization has said the strain involved in this outbreak was a rare one. It's been seen in humans before, but never in this kind of outbreak.
With reports from the Associated Press
