Health experts have warned there could be more E. coli cases across Europe and elsewhere after finding recent deadly outbreaks were probably linked to contaminated Egyptian fenugreek seeds.
They say the fenugreek seeds are likely to blame for a massive food poisoning outbreak in Germany beginning in May that killed 49 people and infected more than 4000, as well as a much smaller outbreak in France in June.
A single E coli case was also reported in Sweden, in a patient with no known links to Germany.
More than 800 people have developed a life-threatening kidney complication after catching the bug.
In a report issued this week by European authorities, the French E. coli strain was found to be genetically similar to the one in Germany.
Fenugreek seeds imported from Egypt are being blamed for both outbreaks, but scientists still haven't found any tainted seeds.
"There's no smoking gun," Ian Henderson, a professor of microbial biology at the University of Birmingham, said on Thursday.
"But it would be unusual to have the same rare strain found in Germany and France without some link."
Fenugreek leaves are commonly used as a herb and also in curry.
If the fenugreek seeds were contaminated at the source - during production in Egypt - they could have been freeze-dried before being sold, allowing the E. coli bacteria to live for years.
Once water is added to grow the sprouts, the entire sprout would be infected and washing wouldn't help get rid of the potentially deadly bacteria.
"Sprouts are biological time bombs," Michael Osterholm, director of the Centre for Infectious Disease Research and Policy at the University of Minnesota, said.
"If they're infected, once they're rehydrated and distributed, they could take the bacteria anywhere."
Osterholm said the seeds could also cross-contaminate other products or be sold in a seed mix.
The European Food Safety Authority recommends people stop growing their own sprouts and not eat any of the vegetables unless they're thoroughly cooked.
Raw sprouts are often used in salads, sandwiches and garnishes.
European food safety and health officials have asked Germany and France to quickly find out where seeds from the suspected contaminated Egyptian batch may have been sold.
French farmers apparently bought their seeds from a British mail-order company.
Germany's consumer protection and food safety agency refused to say on Thursday whether the organic farm in northern Germany implicated in the deadly E. coli outbreak used seeds from Egypt or whether other German farms had received Egyptian seeds.
However, the agency said it was investigating the report.
Experts said it was crucial to trace exactly where the bad seeds ended up but that doing so would be very difficult.
"They might have shipped over a couple of tons of seeds from Egypt, but it could have just been a small amount of seeds that were contaminated," explained Stephen Smith, a microbiologist at Trinity College in Dublin.
"And then some of that shipment goes to Germany, France, and maybe lots of other countries."
Smith said it was likely only a small batch of the seeds were contaminated, which might explain why the new E. coli cases are appearing sporadically.
"We will probably see more cases, but hopefully not on the scale of the German outbreak," he said.
Osterholm said medical authorities should be increasing their surveillance and testing of potential E coli patients, since cases could easily be missed.
"Once seeds are sold from Egypt, they could be distributed all over the world," he said.
"There is no place in the world that's safe from an outbreak like this."