Maine health officials are recording a rising number of illnesses caused by bacteria linked to raw seafood.

Since July 1, four Maine residents and six visitors to the state have been infected with Vibrio, a bug found in raw oysters, clams and other seafood.

While 10 cases of the illness isn’t high, this year’s count is more than double the four cases Maine recorded in each of the last two summers, according to Dr. Stephen Sears, state epidemiologist. Health officials also are investigating a potential 11th case, he said.

The bacteria, which belongs to the same family of germs that causes cholera, occurs naturally in coastal ocean waters. Vibrio thrives in warmer temperatures, and can cause infection when an open wound is exposed to mild seawater.

That’s how most of those sickened in previous years were infected with the bacteria in Maine, Sears said. But this summer, raw or undercooked seafood appears to be the culprit.

Multiple state agencies investigated the illnesses, but so far the cases have been deemed sporadic. The reports of Vibrio turned up in southern and central Maine, and didn’t originate in any particular region of the coast, Sears said.

“We did not find any common denominator,” he said. “We did not find a common distributor or a common restaurant.”

Vibrio can cause vomiting, diarrhea, fever, stomach cramping and skin lesions. While it’s not life threatening to most healthy people, it can lead to shock and potentially death among those with certain medical conditions, such as cancer, diabetes and liver disease. Vibrio is fatal in about half of the people who are at high risk for the illness, according to the U.S. Food and Drug Administration.

Vibrio killed 11 people in 2009 who ate tainted East Coast and Gulf Coast oysters and clams that were served raw or undercooked.

“We tend to see it as a significant illness in people who have an underlying disease or who are also older,” Sears said.

The median age of those infected in Maine this summer is 70, he said.

Symptoms typically appear within 24 hours after eating contaminated seafood. The illness often clears up on its own after about three days.

“It’s pretty intense and it comes on pretty quickly,” Sears said.

Health officials don’t know what’s behind the uptick in Vibrio this summer, but Sears said his best guess is that warmer ocean temperatures have contributed to the bacteria’s growth.

Some cases of the illness in Maine have likely flown under health officials’ radar. People who recover on their own may never visit their doctor or a hospital, and many labs in the state don’t routinely test for Vibrio, Sears said.

He urged seafood eaters to make sure their meals come from a reputable distributor.

To further reduce the risk of a Vibrio infection, avoid exposing open wounds to warm water, thoroughly cook fish and shellfish, use separate cutting boards for seafood, and refrigerate seafood at the appropriate temperature (40 degrees Fahrenheit for refrigerators and 0 degrees Fahrenheit for freezers).

Jackie Farwell

I'm the health editor for the Bangor Daily News, a Bangor native, a UMaine grad, and a weekend crossword warrior. I never get sick of writing about Maine people, geeking out over health care data, and...