At least 50 people in the southwestern U.S. have been sickened with a rare strain of Salmonella that has been associated with consumption of raw tuna sushi in several states, according to the U.S. Centers for Disease Control and Prevention (CDC). CDC said Monday that the agency is working with public health officials in nine states to investigate what it is now calling a multistate outbreak of Salmonella Paratyphi B variant L(+) tartrate(+). The three main states known to be involved in the outbreak are California (29 cases from 6 counties as of May 15), Arizona (9 cases), and New Mexico (6 cases). A CDC spokesperson told Food Safety News that patients from the other six states traveled to the southwest, where they were most likely exposed to the outbreak strain. Health officials in California, Arizona and New Mexico have said that many of the cases were connected to consumption of raw minced or ground tuna used in sushi. The CDC spokesperson said that while many of the patients reported eating sushi, “the investigation has not conclusively identified a food source.” Local and state health officials are continuing to interview patients to gather more information on the foods they ate in the week prior to their illnesses. Ten of 43 patients interviewed (23 percent) have been hospitalized. Dr. Bob England, director of the Maricopa County Department of Public Health in Phoenix, said in a statement released on Friday that there were multiple restaurants involved in the outbreak. “That is strong evidence that the contamination is occurring before it gets to the restaurant,” England said. The outbreak strain of Salmonella does not cause typhoid fever or paratyphoid fever, CDC noted. Food Safety News will continue covering this outbreak as more information comes to light.