Leafy romaine.

Update: On June 28, 2018, the Centers for Disease Control and Prevention declared this E. coli outbreak officially over.

Romaine has become the "it" lettuce.

It's found, of course, in a wide variety of salads and lettuce mixes and turns up in sandwiches, wraps, burritos—anywhere a little crunch is called for.

“Romaine has become America’s go-to salad green,” says Kara Nielsen, culinary trends analyst at the food and beverage consultant firm CCD Innovation. “It’s everywhere.”

More on Leafy Greens

But the popularity of romaine also means that any food safety concerns associated with it have far-reaching consequences. And that's playing out now.

The current E. coli outbreak linked to romaine is caused by a virulent strain of bacteria called 0157:H7, and it has sickened 149 people so far, 64 of whom had to go to a hospital. At least one person has died. Government officials restricted their warning to romaine grown in the Yuma, Ariz., region, where much of nation's winter and early spring romaine is grown. But Consumer Reports advises consumers to avoid all romaine given how difficult it is for them to tell where their romaine is from. (Learn more here.)

It's the second outbreak since late 2017, when at least 66 people across the U.S. and Canada became ill, 22 were hospitalized, and two died. Investigators say the two outbreaks are unrelated, but Canadian health authorities linked the earlier outbreak to romaine. (U.S. authorities have been less conclusive.)

There's nothing at this point that would indicate romaine is more susceptible to foodborne illness than other leafy greens, says James E. Rogers, Ph.D., director of food safety research and testing at Consumer Reports. Indeed, between 1998 and 2016 there were 45 outbreaks associated with E. coli in leafy vegetables reported in the U.S., and the majority of those vegetables were not romaine lettuce, the CDC says.

“We may be seeing more E. coli outbreaks with romaine now simply because we’re growing more of it,” says Rogers.

But romaine's ubiquity has even made the investigation into the outbreaks more difficult.

“It’s so common, many people may not notice—or remember—when they’ve eaten a little romaine,” says Matthew Wise, lead investigator for the Centers for Disease Control and Prevention.

How did romaine get to be so ever-present in American cuisine, and how can you avoid it until this latest outbreak is declared over?

Romaine’s Rising Star

Iceberg once was the king of the salad aisle. But then health-conscious Americans began seeking leafy greens with more nutritional oomph, and sales of the nutritionally poor iceberg began to decline, according to Nielsen.

Romaine was the perfect iceberg stand-in. 

Like iceberg, romaine is crunchy and sturdy, able to stand up to being wrapped up in a tortilla, for instance. These qualities prove especially important in an age when elaborately constructed salads have become de rigueur.

“We need a lettuce that can hold up under cheese and chicken and everything else" Nielsen says. "Romaine is a strong-enough carrier for all your goodies.”

Another sought-after element that romaine shares with iceberg is its relatively mild flavor.

"Compared to greens with a more distinctive taste like, say, kale—nothing against kale; I love kale!—I think romaine has a very versatile flavor profile," says Scott Horsfall, CEO of the industry group California Leafy Greens Marketing Agreement, whose member growers ship 30 million servings of romaine every day.

Also, like spinach or endive, romaine lettuce can be served hot or cold; grilled romaine is a popular preparation at many restaurants.

In addition, romaine has roughly twice as much dietary fiber, potassium, calcium, and iron as iceberg.  

Romaine lettuce now is the most purchased lettuce in America, with 43.2 percent of total sales last year, according to the Consumer Perishables Databook 2017. Iceberg is holding on in the second spot, with 37.3 percent of lettuce sales. Other leafy greens make up a tiny fraction of these sales.

“Romaine used to only show up on menus in Caesar salads,” Nielsen says. “But in roughly the mid-aughts it started becoming the everyday salad base.”

Steering Clear

All of this makes romaine a little difficult to avoid. And E. coli-tainted leaves may still be on shelves through mid-May. The CDC continues to advise consumers to avoid any romaine grown in the Yuma region or when the origin is unclear.

Here's what you can do for now:

• Inspect salad mixes carefully. If a bagged salad—say, a spring mix—doesn’t list all of the greens it contains, avoid it. And if the lettuces are listed, read carefully; romaine is often listed near the bottom.
• Don’t trust your eyes. Chopped romaine can resemble many other greens, so don’t assume you’ll be able to recognize it by sight. If you aren’t sure what lettuce you’re looking at, it’s safer to not eat it.
• Always ask. When you’re ordering a sandwich, wrap, or anything else that may contain lettuce, ask what kind is being used. If the preparer doesn’t know, skip it.
• Substitute other lettuces. Ellen Klosz, a Consumer Reports nutritionist, says red or green leaf lettuce is a decent replacement for romaine in most salads. On a sandwich or wrap, microgreens or arugula can add a burst of flavor. And if you’re craving your Caesar fix, crisp Bibb lettuce is a good stand-in.
• Eat more cooked greens. Not only can sautéing or steaming greens assist in nutrient absorption, the heat can also kill foodborne bacteria. Rogers says you need to raise the greens’ temperature to 165° F to achieve the latter. Romaine is typically served raw or grilled, though. “To get romaine hot enough on the grill to kill bacteria, you’d basically have to burn it to a crisp,” he says. “It’s not worth the risk right now.”

If you have consumed romaine recently, watch for symptoms of infection with E. coli O157:H7. They include severe stomach cramps, diarrhea (often bloody), and vomiting. Some people may have a slight fever. The CDC recommends seeing a doctor if you have a high fever, bloody diarrhea, or severe vomiting, or if diarrhea lasts longer than three days.