Raw tuna in sushi could be to blame for a Salmonella outbreak that has already sickened 25 people from California and elsewhere.
The particular strain had not been seen in humans or animals until last month, which makes the outbreak particularly challenging, according to the Ventura County Public Health Department.
"We are not flying with the experience that we would normally have with this organism," county Health Officer Robert Levin said.
More than 80% of the affected patients reported eating raw tuna as well as sushi, the health department said.
Health officials are still investigating the cause of the outbreak, Levin said, but "right now eating raw fish … probably tuna, can put you at risk."
Eighteen cases have been confirmed in California, including seven in Los Angeles County, four in Orange and Ventura counties, two in Riverside County and one in Santa Barbara County.
The other seven victims live outside California but have visited the state.
One-fifth of the victims had to be hospitalized, health officials said. The illness is treatable with antibiotics but can be deadly.
The California Department of Public Health determined that the strain in question is closely related to another strain responsible for a 2010 outbreak, county officials said.
That outbreak, in California and Hawaii, was linked to raw tuna imported from Indonesia. The two strains, however, appear to be genetically different.
People who have experienced fever, abdominal pains, nausea and diarrhea in the last week and have eaten raw fish should seek the care of a physician, Levin said.
Salmonella has been found in uncooked meat, eggs, chicken unpasteurized milk, cheese, fruits, vegetables and nuts. It is transmitted by pets or through improper food handling.