Streptococcus is usually harmless. But if it gets into an open wound like a foot blister, as it did in this case, it can be deadly.

Foot blisters are a common side effect of hiking, running, and breaking in a new pair of sandals. But one man’s blisters nearly ended his life after they became infected with so-called flesh-eating bacteria—which spread quickly through his body and attacked his internal organs.

Miami resident Wayne Atkins, 32, developed the annoying swellings while hiking in New Hampshire’s White Mountains, according to a news report from New Hampshire TV station He didn’t pay much attention to them, though, until he’d returned to Florida and noticed that they were not healing—and that he’d begun to feel ill.

Worried, Atkins went to the hospital. There, doctors diagnosed him with necrotizing fasciitis, a condition in which bacteria eats away at the muscle and soft tissue directly underneath the skin. The culprit? Group A streptococcus, the same bug that causes strep throat.

Atkins had to be placed in a medically induced coma because his liver, kidney, and lungs were starting to shut down, his mother told WMUR. Thankfully, doctors were able to cut away the affected tissue and administer antibiotics, which helped put the brakes on the infection. He faces a long road to recovery, but “he has his life, he has his leg,” his mother said. “There are many more worse-case scenarios.”

Luckily for the rest of us, necrotizing fasciitis is rare­—and not something people should worry much about when they develop blisters or other small wounds, William Schaffner, MD, an infectious disease specialist at Vanderbilt University Medical Center tells Health. But there are some things we can learn from this frightening story, says Dr. Schaffner, who has not treated Atkins. Here’s what he thinks everyone should know about how to stay safe, and when to see a doctor.

Strep bacteria can be harmless—or extremely dangerous

The bacteria that caused Atkins’ infection, Group A streptococcus, is extremely common; it lives in noses and throats and on skin. Even though it can cause strep throat, for many people, it has no symptoms at all.

But if that same bacteria gets into an open wound—even a “remarkably trivial one” like an insect bite, a scratch, or a blister, says Dr. Schaffner—it can result in a serious infection. “It can be breathed out and get on a person’s fingers, and then if they’re touching their blister it can get beneath the surface,” he says.

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‘Flesh-eating’ isn’t entirely accurate, but it’s close

For an infection like the one Atkins developed to occur, some type of skin tear or puncture is typically involved; this type of bacteria won’t eat through healthy skin all on its own. (The same goes for similar infections that can be caught while swimming with open wounds.)

The term "flesh-eating" can also be misleading because in most cases, the damage is largely done under the surface of the skin. “It’s a nasty infection that causes destruction of the muscle tissue, but it’s not always visible right away,” says Dr. Schaffner. “It can be surprisingly subtle in its early stages.”

Pain is usually the main symptom

Necrotizing fasciitis can trigger redness and swelling, but it’s not always easy to distinguish normal wound healing from a potentially fatal infection, says Dr. Schaffner. The condition can also cause fever, but maybe only a degree or two above normal—not necessarily enough to raise red flags, especially because your temperature tends to naturally fluctuate throughout the day.

Usually, he says, the most telling symptom is pain. “And I mean serious pain, beyond what you would expect just looking at the surface, which often doesn’t look so bad,” he adds.

Patients should seek medical care if a minor wound is beginning to hurt more than it should, says Dr. Schaffner. It’s important you let your doctor know how much pain you're really in. Otherwise, an infection could be missed—or its seriousness could be underestimated—until it progresses and the prognosis is much worse.

Treatment involves surgery and medication

The first step when treating necrotizing fasciitis is for surgeons to cut away the damaged tissue, which can require several operations over several days. “Surgery sounds surprising, since we’re talking about infection,” says Dr. Schaffner, “but to truly get rid of this bacteria, the infected tissue needs to be literally removed.” If the condition isn’t caught very early, entire limbs may need to be amputated.

Patients will also require antibiotics, which kill any bugs that remain and keep them from spreading to other organs. They'll also need supportive care (like fluids, nutrition, and pain relief) at the hospital. Atkins will require skin grafts and rehabilitation sessions to help regain his strength and ability to walk.

Take steps to protect yourself

Hikers in New Hampshire shouldn’t worry about stumbling onto the same strain of strep bacteria that caused Atkins’ illness, says Dr. Schaffner. “It’s very unlikely this came from the environment,” he says. “Nine times out of 10 the person is unaware they have strep in their own body and they inoculate themselves with their own bacteria.”

Even though serious infections like this are rare, it’s still smart to wash off any breaks in the skin with a disinfectant, and to cover them with a bandage to keep out foreign material, says Dr. Schaffner. “And if there’s anything to suggest it’s not getting better the way it should, especially if there’s a lot of pain, have the site examined—and don’t hesitate to ask if the doctor thinks there might be something going on beneath the surface."