With summer's steamy weather, people are flocking to swim in the ocean or soak up the sun, and the more adventurous are perhaps eating oysters on the half shell.

But those summertime activities can have some nasty side effects — including an infection caused by marine bacteria called Vibrio vulnificus. Last week, a Louisiana man died from an infection from the bacteria that he acquired over the July 4th weekend, according to news reports.

The ocean microbe, which is related to the bacteria that cause cholera, is often picked up from eating raw oysters. But V. vulnificus can also enter the body through an open wound, and cause nasty, skin-eating infections, said Kimberly Reece, a molecular geneticist and marine scientist at the Virginia Institute of Marine Science in Gloucester Point, Virginia, who studies the bacteria.

"It's in the environment all the time," Reece said.

But although the bacteria are almost always lurking in the water, they are usually not dangerous for healthy people, Reece said. And there are several steps people can take to prevent serious infection, Reece added. [6 Superbugs to Watch Out For]

Mostly harmless

V. vulnificus tend to multiply in warmer salt water, which means bacterial concentrations can rise dramatically in the summer months. Infections are also more common among people who enter the balmier waters of the Gulf of Mexico and the Atlantic compared with those who wade into the more frigid Pacific Ocean, Reece said.

Most of the time, the bacteria are harmless. But the microbes accumulate in the bodies of oysters and other shellfish. People who eat raw or undercooked oysters run the highest risk of contracting V. vulnificus from food, Reece said.

People can also be infected with the bug if they have an open wound and go swimming in waters with high levels of the bacteria.

Most people face a minimal threat from the bug.

"The only people who usually become very ill with Vibrio vulnificus are people who are diabetic or their immune systems are compromised," Reece told Live Science, adding that not every person who has a weakened immune system knows it.

For those who have ingested the bacteria, typical symptoms include diarrhea, vomiting and severe dehydration. Those who acquire the flesh-eating infection may have what look like raw, open wounds spreading across their skin.

Sometimes, however, people who acquire the infection by either route develop septicemia, or a systemic blood infection, which can kill them, Reece said.

Taking precautions

There are strict regulations for how to handle oysters in the summer months, and oyster farmers will often flash-freeze or dry shellfish immediately after harvesting them to prevent Vibrio vulnificus proliferation, Reece said.

But the surest way to avoid the bug is to not eat raw or undercooked shellfish, especially during the summer months when the bacteria thrive. People should also make sure they are buying their shellfish from reputable harvesters who use safe handling techniques, she added.

People can also avoid the infection by staying out of the water if they have an open cut or sore.

Anyone who develops a nasty-looking sore, or an upset stomach after being exposed to the risk factors, should go to a doctor immediately, according to Reece. V. vulnificus infections can be treated with antibiotics, but treatment is more effective if it's done soon after the infection takes hold.

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