ATLANTA — The Food and Drug Administration (F.D.A.) and the Centers for Disease Control and Prevention (C.D.C.) linked an outbreak of E. coli to romaine lettuce grown in the Salinas region of California.

There was not enough traceback information to identify the source of the contamination and request a recall from specific growers, the agencies said on Nov. 22. They advised restaurants, retailers, suppliers and distributors to voluntarily withdraw product grown in the region and withhold distribution of Salinas romaine for the remainder of the growing season.

Michael W. Droke, partner at the international food and agriculture law firm Dorsey & Whitney L.L.P., said the warning will likely affect other products.

“A warning like this, especially during the holiday week, will impact not only romaine, but other leafy green vegetables such as spinach,” he said. “Retailers will be pulling romaine and possibly all other lettuce and leafy greens from their shelves.”

As of Nov. 21, 40 people infected with E. coli 0157:H7 in 16 states have been reported, according to the C.D.C. Patients said the illness started between Sept. 24 and Nov. 10.

The Maryland Department of Health identified the outbreak strain in a package of Ready Pac Bistro Chicken Caesar Salad collected from a patient’s home. Analysis of the salad linked the strain to three Maryland cases and the multi-state outbreak.

The F.D.A. and state partners are conducting a traceback investigation to determine the source and extent of the contamination. Preliminary information indicated ill people in Maryland were exposed to romaine harvested in Salinas. The region, which includes Santa Cruz, Santa Clara, San Benito and Monterey counties, produces 61% of the nation’s leaf lettuce, according to the Monterey County Farm Bureau.

Analysis of the E. coli strains from patients in the current outbreak resemble the strain associated with previous outbreaks in 2017 and 2018, the F.D.A. said. The 2017 outbreak was associated with leafy greens in Canada and the U.S. More than two dozen people across 15 states were infected with the strain, which eventually led to one reported death in California. Officials were unable to locate its source. 

Last year’s outbreak originated from tainted romaine grown in Santa Barbara county. Sixty-two people in 16 states were affected.

The news of the outbreak was met with frustration by Californian lettuce farmers. Last year’s outbreak, caused by lettuce grown outside of Salinas, resulted in the region losing more than $160 million. 

“No one is more frustrated than the producers of leafy greens that outbreaks continue to be associated with our products,” said Scott Horsfall, chief executive officer of the California Leafy Greens Marketing Agreement (L.G.M.A.), a food safety program created in 2007 to prevent foodborne illnesses in lettuce and leafy greens.

Producers have been voluntarily labeling romaine lettuce with information on harvest date and growing regions since last year. The L.G.M.A. said it hopes these efforts will reduce the impact of the outbreak.