Salmonella outbreak linked to raw fish consumption

NEW YORK (Reuters Health) - Eating contaminated raw tuna can be a cause of Salmonella infection, a researcher from Hawaii warned on Tuesday.

In November 2007, the Hawaii Department of Health (HDOH) was alerted to 16 cases of Salmonella infection. An epidemiologic investigation at the time failed to uncover the source of the outbreak.

In hopes of identifying the source, the HDOH conducted a case-control study involving 35 "case" patients that arose from October 2007 to February 2008 and 100 age-matched controls who lived within a 0.5 mile radius of a matched case patient.

The only significant correlate of Salmonella infection was raw fish consumption in the 7 days before illness onset. Eighty-six percent of case patients had consumed raw fish compared with just 28 percent of controls.

In most cases, ahi "poke," which is often made from imported frozen tuna, was the fish consumed. The investigators could identify no single store, store chain, or supplier that accounted for all of the exposures.

"There have been very few, if any, studies or investigations, of which we are aware, examining salmonellosis following raw fish consumption, although there are reports of finding Salmonella strains in samples of fish product meant for export and ultimately human consumption," Dr. Sarah Park, who is with the HDOH in Honolulu, told Reuters Health.

"We had initially thought that, as with most salmonellosis outbreaks, the source would likely be poultry or some other commonly recognized source. Finding that raw fish consumption was the culprit was surprising," said Park.

She emphasized that, "compared with the thousands of tons of fish imported into Hawaii and consumed every month, this was a small outbreak. However, as always, everyone should be aware that consumption of any raw meat product carries some risk, and should they develop a gastrointestinal illness, they should make sure their clinician is aware of their potential exposures."

Raw tuna-associated cases of Salmonella infection are not confined to Hawaii. As recently as April 2008, nine electrophoresis-matched cases of Salmonella infection were reported in mainland US, eight of which involved consumption of raw tuna prior to disease onset.