A 71-year-old man needed his forearm amputated after eating raw seafood, according to a case report in a recent issue of the New England Journal of Medicine.

The unnamed man went to a South Korea emergency room after having a fever for two days and “excruciating pain” in his left hand. The cause? A dark purple blister covering much of his palm, with more swelling and discoloration on the back of his hand. Twelve hours before the blister developed, he had eaten raw seafood, according to the NEJM.

Image zoom Jin Park, M.D., Ph.D., & Chang-Seop Lee, M.D., Ph.D./Nejm.org

When doctors performed surgery on the blister, they found the man was infected with Vibrio vulnificus, bacteria that usually cause GI symptoms like vomiting, diarrhea, and stomach pain but is sometimes referring to as “flesh-eating.”

Despite treatment with antibiotics, the man—who had a history of type 2 diabetes, high blood pressure, and kidney disease—didn’t get better. The bacteria caused “deep necrotic ulcers,” according to the report, and 25 days after first going to the ER, he had his left forearm amputated. (Luckily, that surgery went well and he was sent home.)

The authors of the case report warn that contact with V. vulnificus is a known risk of consuming raw or undercooked seafood. In fact, in June, another 71-year-old man died from an infection with the bacteria, called vibriosis, after eating raw oysters. The Centers for Disease Control and Prevention (CDC) estimates that about 80,000 people get sick with vibriosis every year and approximately 100 of those people die; around 52,000 of the annual cases are caused by eating contaminated food.

So why is raw or undercooked fish especially dangerous? Vibrio bacteria live in salt or brackish water, and if they're contaminating the water, they can contaminate seafood, too. Raw oysters and other filter feeders are especially problematic. Some people also get vibriosis from swimming in contaminated water with an open wound, like the man who died from it in 2017 after taking a dip with a new tattoo.

Before you panic about your last tuna avocado roll, know that it’s usually only people with weakened immune symptoms due to underlying health conditions who face such dire consequences after encountering Vibrio bacteria. If you’re otherwise healthy, you’re much more likely to fight off a vibriosis infection before it becomes dangerous.