WASHINGTON -- Federal health officials are investigating a growing outbreak of salmonella that has sickened 90 people in 19 states and the District of Columbia, according to a Food and Drug Administration memo.

The outbreak is “rapid and expanding in number of cases,” with seven hospitalizations reported, according to a memo distributed to FDA staff Tuesday morning. No deaths have been reported to date.

The salmonella may be linked to sushi and investigators are focusing on spicy tuna rolls as “highly suspect.”

Reports of the foodborne illness have mainly come from the eastern seaboard and Gulf Coast, though cases have been reported as far west as Missouri and Texas. Investigators are focusing on six clusters of restaurants in Texas, Wisconsin, Maryland, Rhode Island and Connecticut.

FDA spokesman Curtis Allen would not confirm or elaborate on the information, saying the memo “contains numbers of cases and hospitalizations that cannot be confirmed at this time.”

“It is too early to speculate on the cause of the outbreak,” Allen said.

The FDA is working with the Centers for Disease Control and Prevention and state officials to identify the source of the outbreak. Investigators conduct interviews with sick patients about what they’ve eaten and analyze menus and food ingredients to trace the path of the bacteria.

The memo notes there is likely a 30-day lag time between when people become sick and when cases are reported to health officials.

Previous outbreaks of salmonella bareilly have been linked to bean sprouts, which are grown in warm, damp conditions.

The most common symptoms of salmonella are diarrhea, abdominal cramps and fever within eight to 72 hours of eating the contaminated food. The illness can be life-threatening in people with weakened immune systems.