Red onions grown in California have been traced as the potential source of a salmonella outbreak that has infected more than 500 people in the United States and Canada, health officials said.
Confirmed cases have surfaced in 34 states. Those most affected as of Saturday included Oregon (71); Utah (61) and California (49), the Food and Drug Administration said.
The Public Health Agency of Canada reported that the country had 114 cases of salmonella and that at least 16 people had been hospitalized. In the United States, 396 illnesses and 59 hospitalizations have been reported, the F.D.A. said.
The administration said it was able to identify Thomson International, a produce supplier in Bakersfield, Calif., as a likely source of contaminated red onions.
Thomson said on Saturday that it recalled red, yellow, white and sweet onions that were shipped since May 1 because of the risk of contamination.
Onions were distributed to wholesalers, restaurants and retail stores across the country and in Canada, Thomson said. They were also distributed in mesh sacks and cartons under the names TII Premium, El Competitor, Hartley, Onions 52, Imperial Fresh, Utah Onions and Food Lion.
Health officials recommend that consumers throw away any onions or foods made with onions supplied by Thomson, and in general throw away onions if they were unsure of where they came from.
The illness, named salmonellosis, can persist for four to seven days, the agency said. Children, older adults and people with weaker immune systems are most at risk to develop severe illness.
Symptoms include diarrhea, fever and abdominal cramps. Those who are severely ill may also experience a high fever, headaches or a rash.
Salmonella can be spread when the hands, surfaces and tools of food handlers are not clean, and when people eat raw or undercooked food, health officials said. It can also be spread to people from animals.
The Centers for Disease Control and Prevention estimates that salmonella causes about 1.35 million infections and 26,500 hospitalizations in the United States each year. Although most people can recover without treatment, more than 400 deaths in the United States each year can be tied to acute salmonellosis.
Almost 1,000 cases of salmonella in 48 states have already been linked this year to contact with backyard poultry, including chicks and ducklings, according to the C.D.C.
At least 151 people have been hospitalized so far this year and one person in Oklahoma has died. More than a quarter of those who have become ill are younger than 5 years old.
In 2019, 165 cases of salmonella in 14 states were caused by pre-cut fruit, like honeydew melon, cantaloupe, pineapple and grapes, the C.D.C. said.