Can you eat leftover sushi?

How could old or improperly handled sushi make you sick?

Food safety experts worry most about parasites, like tapeworms, in raw fish, but fortunately those can be eliminated by freezing in specific ways. Responsible sushi purveyors serve fish that’s been frozen at a specified temperature for a designated period of time to nix parasites. (Don’t try this at home – a freeze in a home fridge could help, but is unlikely to get cold enough for long enough to do the job properly.)

But the deep cold can’t be relied on to kill a whole medley of pathogenic bacteria that could be present on sushi and could boost their numbers (and therefore their ability to make you sick) as the sushi sits out at room temperature. That includes salmonella, Listeria monocytogenes, vibrio and dangerous strains of E. coli, all of which cause highly unpleasant gastrointestinal symptoms and worse. Their presence wouldn’t impact the flavor of the sushi (though if spoilage microbes were working simultaneously, you’d notice the sushi tasting off). But a higher load of pathogens, which you’d get if you ate older sushi, particularly older sushi that had been at room temperature for a while, makes them more likely to make you sick.

According to food safety guidelines, finfish should be cooked to about 145 degrees Fahrenheit to be microbiologically safe, but that, of course, doesn’t happen during sushi prep. And even cooking the sushi isn’t enough if the food has sat out at room temperature for an extended period of time; some pathogens produce toxins that can’t be nixed by cooking. And some pathogens can contaminate a food after it’s prepared and served. This is why I wouldn’t pull my sushi-cooking trick on maki, nigiri and sashimi that had sat out all day. 

Listeria contamination would be particularly worrisome, Hellberg said, because this bacteria can grow in the fridge. Listeria is tricky because it’s somewhat widespread in the environment, including on uncooked foods, but rarely causes illness because healthy adults need to consume a large load to get sick. The trouble is that immunocompromised people can get extremely sick if they consume relatively small amounts of listeria, which is why pregnant women are told to entirely avoid foods like sushi that contain raw fish.

How often is sushi actually contaminated? 

So while it is possible for all those terrible things to be on sushi, it doesn’t mean they’re there (you’d have no way of knowing by simply looking at or eating the sushi). And while strict protocols aren’t foolproof, careful handling makes it harder for raw fish to be contaminated. A couple years ago, Hellberg and her fellow researchers examined sushi, poke and ceviche purchased at a variety of restaurants and grocery stores in Orange County, California. They tested their samples within four hours of purchasing them and didn’t find any salmonella or Listeria monocytogenes. So, phew!

They did find E. Coli, though Hellberg said it was within acceptable limits (while some kinds of E. Coli can cause illness, others are harmless and can even be beneficial; Hellberg’s group tested for generic E. Coli and did not evaluate what kind of E. Coli they found). The researchers also found spoilage organisms that wouldn’t make you sick, but would make the food go bad faster. 

“Our study found several spoilage organisms in raw [ready-to-eat] seafood, including Pseudomonas aeruginosa, Morganella morganii, and coliforms,” Hellberg wrote to me. “These organisms can affect taste, smell, and texture, signaling that the seafood is no longer good to eat.”

Hellberg’s study is encouraging evidence that sushi purveyors are doing a good job keeping the baddies out of sushi, but it’s still one study in one market and caution is always warranted.

How often do people actually get sick from eating sushi?

“Reported outbreaks linked to sushi are relatively rare, especially considering its popularity,” Hellberg wrote. “This is likely due to a combination of factors, including strict sourcing and handling protocols in reputable establishments, freezing requirements for raw fish intended for sushi (these kill eukaryotic parasites but don’t necessarily kill bacterial or viral pathogens), and underreporting of mild or isolated cases.”

This Centers for Disease Control and Prevention database lists 45 outbreaks linked to sushi between 2015 and 2015. By contrast, for chicken that number is 366. Of course, people probably eat sushi less than chicken, and, as Hellberg notes, mild or isolated cases don’t get counted as outbreaks. And mild or isolated cases are the most likely outcome if an individual is sickened by sushi they mishandled at home. 

Overall, if you have some leftover sushi that feels iffy to you, here’s Hellberg’s take:

“Consumers should treat sushi with extra caution compared to other leftovers. When in doubt, it’s safer to discard sushi that’s been sitting out or stored too long. Also, consumers should purchase sushi from reputable sources that follow proper food safety protocols.”