Just because they're frozen doesn't mean they can't harbor foodborne illnesses.
When you think of food-borne illnesses, foods like undercooked meat and leafy greens probably come to mind. What you likely do not think about is frozen fruit, but the Food and Drug Administration wants that to change. Even though it's often eaten raw and may seem totally benign, frozen fruit can still pose a health risk.
The FDA is currently undergoing a 'surveillance sampling' of frozen fruit brands, looking for hepatitis A and norovirus, two of the most common food-borne illnesses. When it detected hepatitis A in packages of frozen blackberries and blended berries sold by Kroger and Costco earlier this summer, it issued two recalls, despite there not being any outbreaks detected.While it says it doesn't want the public's perception of frozen berries to change – eating fruit is good! – it wants people to be aware that outbreaks can and do occur. The Washington Post reported,
"Frozen berries caused three hepatitis A outbreaks and one norovirus outbreak in the United States from 1997 to 2016. Nearly 550 people were sickened and 53 had to be hospitalized. There were no reported deaths."
The problem is more serious in Europe, where frozen berries caused a hepatitis A outbreak between 2013 and 2014 that sickened over 1,500 people.
Freezing does not kill these viruses; in fact, that's the way scientists keep them alive for lab work. The only way to be absolutely sure is to cook frozen berries, bring them to a boil, then cool and refreeze. This is what microbiologist Benjamin Chapman does, just to be safe when making his daily smoothie.
The same concerns apply to frozen vegetables, but it's even more serious because the producers tend to assume the food will be cooked before eating, which makes health and safety procedures more lax. From the Washington Post: "The food processing industry doesn’t treat frozen vegetables as ready-to-eat foods. As Chapman said, 'They are expecting us, the consumers, to cook them.'"
While the news is alarming, I can't see myself going to the lengths that Chapman does to make his smoothies, but then I'm also careful about where I source my fruit. I try to pick as much as I can from a local pick-your-own fruit farm and then freeze it on baking trays before transferring to a container for use all year round. When I ran out last winter, I bought a bag of strawberries that, much to my horror, had come from Chile. When fruit is traveling that far, it's not hard to imagine it picking up some nasty stuff along the way.
The point is, be aware of the risks. Keep your freezer shut to prevent the introduction of warm air. When cooking frozen fruit, check with a thermometer to ensure it reaches 212 degrees F, and make a point of doing this when preparing food for babies or children, pregnant women, or the elderly. Shorten the route from farm to table to reduce risk of contamination; buy fruit from local farmers and markets and eat what's in season.