LOS ANGELES, May 21 (Reuters) - An outbreak of salmonella believed to be linked to raw tuna in sushi has sickened at least 53 people in the United States, mostly in California, officials said on Thursday.

The U.S. Food and Drug Administration said in a statement an investigation has not identified which supplier of raw tuna might have been responsible for the outbreak, which so far has led 10 people to be hospitalized but has not caused any deaths.

There are no specific steps for consumers to take to protect themselves at this time, the agency said on its website. But it said that in general certain susceptible groups, such as pregnant women and young children, should not eat raw or partially cooked fish.

In California, 31 people have become ill from the outbreak in six counties, including Los Angeles and San Diego counties, according to the California Department of Public Health. The other eight states where people were sickened include Arizona which had 10 cases and New Mexico which had six.

“As the investigation continues, this is a good reminder to Californians that there are sometimes risks when eating raw or undercooked meats, fish or poultry,” California Department of Public Health director Dr. Karen Smith said in a statement.

Illnesses tied to the outbreak occurred between March 5 and May 3, according to the U.S. Centers for Disease Control and Prevention (CDC).

Nearly all the sick people who were questioned by health workers reported consuming sushi with raw tuna before they became ill, and most of those specifically said they ate “spicy” tuna, according to the CDC.

Symptoms of the illness include diarrhea, fever and abdominal cramps. Most patients recover without any treatment, according to the California Department of Public Health. (Reporting by Alex Dobuzinskis; Editing by Sandra Maler)