The state Department of Health and the U.S. Food and Drug Administration are investigating a series of illnesses caused by salmonella in Hawai'i, Colorado and California that may be linked to imported frozen 'ahi that was consumed raw.

Hawai'i typically has more than 300 cases of salmonella poisoning a year, which causes a severe diarrheal gastrointestinal illness. The 32 recent cases that prompted the investigation were reported between Oct. 27 and Dec. 29, and stood out because they were caused by a strain of salmonella not normally seen in Hawai'i, state health officials said.

Outbreaks of that strain — Salmonella paratyphi B — have been associated with smoked white fish, unpasteurized milk and goat cheese and alfalfa spouts, and normally only about 10 cases are reported here a year, said Health Department spokeswoman Janice Okubo. That particular type of salmonella also is associated with ornamental fish, turtles and reptiles.

All of the cases in the Hawai'i cluster were on O'ahu, and five of the 32 people here who became ill were hospitalized, according to a Health Department medical alert on the subject. An additional Hawai'i case that may be caused by the same type of salmonella was reported this year, but has not yet been confirmed.

Okubo said the Health Department will not identify any retail outlets the tainted fish could have come from because "there needs to be more product tracing in order for someone to determine the source."

"To implicate a store that maybe is not purchasing from that distributor anymore wouldn't be an accurate piece of information for somebody today," Okubo said.

Dr. Paul Effler, state epidemiologist for the Health Department, said interviews of the Hawai'i people who became sick "almost universally" implicated 'ahi poke, and health officials also were informed of two similar cases in Colorado and one in California.

Checks of the DNA fingerprint of the bacteria matched the major strain in Hawai'i. That suggested the fish was likely imported and distributed across a number of states, which prompted the Health Department to bring in the FDA on Jan. 11, Effler said.

The FDA is still trying to identify the distributors of each of the establishments that may have been the source of contaminated fish, which has been complicated because the volume of fish is high, Effler said.

Effler said that while there have been more Salmonella paratyphi B cases than normal, it appears to be "low-level" contamination, meaning relatively little of the large overall supply of 'ahi is tainted.

Despite the large amount of fish consumed over the New Year's holiday, Effler said, there hasn't been a surge in cases, suggesting the contamination is limited.

"We want to find the source and make sure we can prevent any illnesses; that is our goal," he said. "At the same time, the fact that the cases are sort of sputtering along and appear to be associated with a vehicle in Hawai'i that is widely consumed, it would suggest the risk is not zero, but it is probably fairly low."

Reach Kevin Dayton at kdayton@honoluluadvertiser.com.