A multi-state outbreak of infections caused by E. coli bacteria has occurred — and while Canadian health officials believe romaine lettuce is the source, American officials aren’t sure yet.

The Centers for Disease Control and Prevention confirmed in late December that it’s investigating (along with the Food and Drug Administration and state governments) an E. coli outbreak that infected at least 17 people — sending five people to the hospital and killing at least one, according to the CDC. The outbreak hit 13 states between mid-November and early December; no new cases have been reported since then.

Since then, the CDC has said that the likely source of the outbreak “appears to be leafy greens,” but warned that officials have not settled on a specific type that is to blame. The CDC has said it is still investigating, and noted that genome sequencing on samples of the bacteria indicated the U.S. and Canadian outbreaks might be linked.

Across the border, Canadian public health officials are investigating their own E. coli outbreak, which sickened at least 41 people and caused one death. American public health officials suggested the two outbreaks could be caused by the same strain of bacteria. “Preliminary results show that the type of E. coli making people sick in both countries is closely related genetically, meaning the ill people are more likely to share a common source of infection,” a spokesperson for the CDC said in an email.

In Canada, authorities issued a public health notice saying that initial findings indicate that contaminated romaine lettuce was the source of the outbreak. The nation’s Public Health Agency went so far as to recommend residents of five provinces “consider consuming other types of lettuce, instead of romaine lettuce, until more is known about the outbreak and the cause of contamination.”

But here in the U.S., officials at the CDC or the FDA have taken a different approach and decided not to issue such a warning. “Because CDC has not identified a specific type of leafy greens linked to the U.S. infections, and because of the short shelf life of leafy greens, CDC is not recommending that U.S. residents avoid any particular food at this time,” the agency said.

This inaction from the CDC and the FDA has prompted sharp criticism in recent weeks from consumer advocates. “The FDA should follow the lead of the Canadian government and immediately warn the public about this risk,“ Jean Halloran, director of Food Policy Initiatives at Consumers Union, told Consumer Reports. “The available data strongly suggest that romaine lettuce is the source of the U.S. outbreak … If so, and people aren’t warned, more may get sick.”

Don’t miss:‘Raw water’ competes with bottled water and soda — why you should avoid all threeCan boxed water compete against bottled water? Water companies are turning to environmentally-friendly packaging - and sales have doubled in the last two years.

Why there is still cause for concern

When bacterial contamination stems from something highly perishable like romaine lettuce, outbreaks are usually more short-lived, said Bill Marler, an attorney who represents victims in cases involving food safety. “The illnesses extend over a month, and that’s unusual,” he said. “Normally when you see an outbreak with a perishable product, you’ll see an outbreak over a week.”

Plus, Marler said that the relatively small number of people made ill could actually indicate a larger outbreak, since many people may not be made ill enough by the bacteria to result in visiting a doctor.

This all points to two possibilities: Romaine lettuce may not be the source of the outbreak. Or, perhaps more concerning, it could be an indication of manufacturing-related issues, Marler said. “Either that, or the food that caused the outbreak was produced on a farm that had a contamination, Marler said.

The long duration of the outbreak in Canada has also prompted officials there to investigate other potential sources.

Why people should avoid romaine lettuce (and other foods) anyway

Nevertheless, the hesitancy on the part of U.S. public health officials stumped Marler. “There’s always a balance with these health officials between outing a company or product and giving the public information to protect themselves, but it’s perplexing to me that this has been going on for a long period of time without naming a product,” he said.

Consequently, Marler suggested that people toss the romaine lettuce sitting in their fridges for the time being. Consumer Reports similarly advised that people avoid romaine lettuce until public health officials provide more information. Both Marler and Consumer Reports argued that the abundance of caution was warranted because romaine lettuce is nearly always consumed raw and washing alone isn’t guaranteed to rid the produce of the bacteria.

Also see:Americans are eating more red meat — why that’s good news

A group of produce industry associations pushed back against such calls given the lack of CDC confirmation regarding the cause of the outbreak and how perishable lettuce is. “No public agency has contacted any Romaine lettuce grower, shipper or processor and requested that they either stop shipping or recall product already in the marketplace,” they said.

But health-conscious consumers may want to be careful, and not only around romaine lettuce — other foods are susceptible to contamination from E. coli and other bacteria. For instance, Marler said he never eats pre-washed bagged salad mixes or pre-cut fruits because the more that raw produce is handled the greater the likelihood of bacterial contamination. Instead he purchases ingredients separately, washes and prepares them.

Generally speaking, leafy greens and herbs are at a higher risk of contamination, particularly in the summer months, according to a 2016 study by the Canadian Food Inspection Agency. However, even among these foods, incidents of food-borne illness are considered rare.

Marler further suggested consumers avoid everything from sprouts (a notable E. coli outbreak stemming from sprouts sickened roughly 3,000 people in Germany in 2011), raw juices and milk. And consumers should certainly steer clear of under-cooked meat, unpasteurized raw eggs and raw shellfish. And pregnant women and people with compromised immune systems may want to put the fork down where cantaloupe is concerned, since it is a common source of listeria — a 2011 listeria outbreak tied to the melon was responsible for more than 30 deaths.