The Public Health Agency of Canada has issued a warning -- but no recall -- about eating romaine lettuce after a deadly outbreak of E. coli O157 bacteria.

At least one person has died and dozens more have fallen seriously ill in an outbreak that has been traced to romaine lettuce, however the federal agency hasn't been able to yet figure out which farm or produce distributor is the source of the contamination.

Because a specific source can't be determined, the agency will not issue a recall. Instead it is urging people to avoid eating romaine lettuce.

The most recent update was delivered on Thursday, when Public Health said there were 40 cases of people falling ill in Ontario, Quebec, New Brunswick, Nova Scotia, and Newfoundland and Labrador.

Sixteen people were hospitalized and one person died.

Dr. Annick Gauthier, a family medicine resident in Montreal who did her Ph. D. research on E. coli bacteria, said those with weak immune systems are most at risk.

"With romaine lettuce and actually with any food, anyone can be infected, but the people that are going to be the most sick are the very young and the very old and that's what we see in all these types of outbreaks," said Dr. Gauthier.

In this outbreak the youngest victim is four years old, and the oldest is 85.

Dangerous time for health warning

Sylvain Charlebois, a researcher in food distribution and policy at Dalhousie University, says these kinds of outbreaks are particularly dangerous during the holiday season, when people have busy schedules and generally do not watch what they eat.

He said it's unusual for an outbreak to last more than a week without a recall, suggesting better traceability systems for produce are needed to pinpoint the cause especially because produce can change hands up to 10 times before it reaches a store.

"So when you have a situation like this, if you are using new technology, you can trace problems very quickly," he said. "But now we have a case where traceability is probably an issue. ... I would say the weakest aspect of our food safety system is traceability."

E. coli O157 symptoms

The O157 strain of E. coli that makes people sick is found in healthy cows and their manure, then gets transferred to what people eat.

"The main places that we get E. coli contamination are water runoff onto things like lettuce, in the news now, but also from contaminated meat," said Dr. Gauthier.

Meat will usually be contaminated when cattle is butchered, with the intestines being perforated, or butchered meat comes into contact with feces.

While most strains of E. coli don't cause disease in humans, the strains that make people sick have similar symptoms.

Anywhere from one to ten days after contact with the bacteria, a person can develop:

  • nausea
  • vomiting
  • headache
  • fever
  • severe stomach cramps
  • watery or bloody diarrhea

Most people recover on their own, but some people develop a more serious illness that requires hospital care and could lead to seizures, strokes, kidney failure, and death.

How to prevent infection

Romaine lettuce has a shelf life of up to five weeks, so it is possible that contaminated produce has been in people's homes for some time -- or is still being sold in stores.

"Based on the investigation findings to date, exposure to romaine lettuce has been identified as the source of the outbreak, but the cause of contamination has not been identified," the agency said. "The outbreak appears to be ongoing, as illnesses linked to romaine lettuce continue to be reported to the Public Health Agency of Canada. These illnesses indicate that contaminated romaine lettuce may still be on the market."

Because no recall was issued grocery stores throughout eastern Canada continue to sell romaine.

Food contaminated with E. coli bacteria will not look or smell spoiled.

"People can protect themselves through really common sense things. Washing their hands before and after, as well as making sure they're rinsing off their vegetables as well as cooking their meat appropriately," said Dr. Gauthier.

Lettuce should not be soaked in a sink because that could cause contamination from other bacteria.

People should wash and dry all utensils, counter tops, cutting boards and storage containers to avoid cross-contamination.

With a file from The Canadian Press