I like sushi, the raw fish kind, but I’m picky about where I eat it, and with each outbreak I’m becoming more apprehensive about consuming it

When I do choose the raw fish-dish, I ask about whether it’s sushi grade and was previously frozen (to take care of the parasitic worms). I stay away from ground tuna or back scrape (which I learned about after a 2012 Salmonella outbreak) since lots of handling and small pieces can increase my risk of foodborne illness. 

Lydia Zuraw of NPR’s food blog, The Salt writes about a sushi-linked outbreak earlier this year, and points out that freezing isn’t good a Salmonella control measure.

The outbreak in question began in California in March. All told, it sickened 65 people in 11 states. There were 35 cases in California, with another 18 in Arizona and New Mexico. The rest of the cases were scattered across the country, including four in Minnesota.

So if pathogens like Salmonella don’t usually contaminate fish, what went wrong with the sushi tuna in this case? The FDA tells The Salt it doesn’t know for sure. Maybe someone in the processing facility didn’t wash their hands. Maybe the water or equipment used in processing was contaminated. Or maybe a bird or rodent got into the fish on the boat or during the ride to the processing facility. There are many opportunities for contamination to occur between capture and processing.

Ironically, freezing is usually considered a way to make sushi safer, because it kills any parasitic worms living in the raw fish flesh. That’s why last month, New York Citybegan requiring sushi restaurants to freeze their fish before serving it. Many of the city’s top sushi spots have been freezing their raw fish for this very reason for years.

But as this case highlights, freezing doesn’t guarantee your sushi is pathogen-free. While freezing will slow down the growth of Salmonella, cooking or pasteurizing are the only ways to kill the bacteria.