An outbreak of salmonella that has sickened 31 people in six counties across Southern California has been linked to the consumption of raw tuna, public health officials said Thursday.

The California cluster was part of a nine-state Salmonella Paratyphi B outbreak, according to a news release from the California Department of Public Health.

Most of the 53 patients nationwide reported eating sushi containing raw tuna before becoming ill, the release stated.

To date, 10 patients have been hospitalized. No deaths were reported.

The California-based cases were spread over six counties, including nine in Los Angeles, six in Orange, four in Riverside, seven in San Diego, one in Santa Barbara and four in Ventura, according to the department.

The illnesses were reported between March 5, 2015, and May 13, 2015. The ages of the patients ranged from less than 1 to 83 years old.

The exact source of the outbreak was unknown, the CDPH stated.

Salmonella symptoms can include diarrhea, fever and abdominal cramps 12 to 72 hours after infection, the department said. Most patients recover without any treatment, but some patients may need to be hospitalized because of the severity of the diarrhea. The disease can cause death if not treated promptly, the release stated.

Details about salmonella are at CDPH’s website. Information about the U.S. Food and Drug Administration investigation is at the FDA website.