This summer, as the mercury rises and sweaty residents flock to area beaches, health department officials find themselves in a sticky spot.

Do they warn residents of the rare but potentially fatal risk of contracting Vibrio, a bacterium that lives in the water and thrives in July and August? Or, when the chance of infection is so small, is it better not to draw attention to such a rare condition and thereby not risk compromising the tourism industry?

The question comes after a Calvert County, MD, man nearly died last year when he contracted Vibrio through a cut in his leg. Overall, Maryland averages about 25 cases of the infection a year, according to state health officials. In most cases, the infections are not fatal. But an Eastern Shore waterman died about six years ago after exposure to Vibrio when he went into the water with a cut.

And, the infections are often serious enough to trigger hospital stays and extensive rehabilitation. If a patient who has contracted Vibrio becomes septic, there is a 50 percent chance of death.

Vibrio vulnificus is a bacterium that lives year-round in the Chesapeake. For the vast majority of people, it is harmless. But those who ingest undercooked seafood or enter the water with a cut are at risk for infections. In the Chesapeake Bay region, the majority of the cases come from exposure through cuts instead of through eating seafood.

According to a Chesapeake Bay Foundation report released last year, the number of Vibrio infections reported in Virginia annually has risen steadily over the last decade. The Virginia Health Department reported four cases in 1999, and three cases in 1998. But the CBF said the state was up to 30 cases in 2008. A Virginia health department spokeswoman said that while the CBF got its numbers from her department, it's not entirely clear what accounted for the increase.

Last autumn, at the beginning of the holiday season, the Virginia Health Department warned residents about eating raw shellfish because of Vibrio. It has a fact sheet on its website reminding people to wash and bandage cuts they may have gotten while in the water. But it also reminds people they should "continue to enjoy water activities on the Chesapeake Bay."

Vibrio from shellfish consumption accounts for only one case or less each year, according to Robert Croonenberghs, director for the Virginia Health Department's Division of Shellfish Sanitation. Those cases have not been fatal. All the same, the state a few years ago required aquaculture operations that harvest oysters in the heat of summer to get them into a refrigerator by 10 a.m.

Local health departments "have some burden to put the information out there in the marketplace. I don't know that they need to flip out or sound a panic gong," said Patuxent Riverkeeper Fred Tutman, who became concerned last year about the lack of warnings after four people were affected in his river. "Look at those signs in restaurants telling employees to wash their hands. No one looks at those and says, 'oh my God, the food ain't good here.'"

During the last five years, a consortium of researchers has been looking into better models to predict where Vibrio vulnificus occurs both in the Chesapeake and the Maryland Coastal Bays. They can now predict where the Vibrio is going to be 93 percent of the time, according to John Jacobs, an ecologist with NOAA's Oxford Cooperative Lab.

Temperature and salinity are the best gauges of where Vibrio thrives. Its preferred salinity is 11.5 parts per thousand, putting it squarely in the Mid Bay region for much of the summer. (Virginia waters tend to be much saltier.) More than 90 percent of the cases occurred when water temperatures were greater than 78 degrees.

"We're getting a really good understanding of the ecology of the organisms, but there's still a big gap in understanding your risk of exposure, and your risk of becoming ill when you encounter these organisms," Jacobs said. "This is an organism that is being controlled by physical factors. It's not something where you can shut off a pipe. So, how do you prepare folks? We can't tell you, if you go in the water, what your risk is. We know where these things are going to be, but we don't want to send the wrong message."

Jacobs said there have been some questions about how to get the information out. Some health officials want to put models on the web, where residents can assess their risks. Others don't.

Clifford Mitchell, assistant director for environmental health and food protection at the Maryland Department of Health and Mental Hygiene, said he would give swimmers, boaters and watermen the same advice regardless of what the models say: Cover any open wounds before you enter the water, wash yourself when you get out and wash your hands thoroughly before you eat anything. He also would advise anyone with a compromised immune system - a cancer patient, for example, or anyone with liver problems - that they are at increased risk.

"In general, we don't know in all cases where people got exposed. We advise these same precautions in all circumstances," Mitchell said. "No one is basing a decision on whether to go to the beach based on the model, and I certainly wouldn't."

Health departments vary in their zeal to warn people about potential problems. In Anne Arundel County, several communities pay biologist Sally Hornor to test their water for harmful bacteria so they can warn residents if swimming is safe. The information is public and posted on Hornor's Operation Clearwater site. The county health department does its own testing of beaches for fecal bacteria, which it posts on its site,

Last year, Anne Arundel County saw nine cases of Vibrio. When a lab test shows a positive result for the bacteria, the health department is notified.

"We call the individual, we call their doctor. We do a long questionnaire to figure out where it came from," said Anne Arundel County Deputy Health officer Kelly Russo. "We take Vibrio very seriously here."

Russo said the department issues the same sorts of warnings Mitchell does, through the website and through yearly articles in the local press. The department doesn't post particular beaches with Vibrio warnings because, she says, the bacteria is "all over the place" and generally not in one river system. The county has nearly 500,000 people and 500 miles of shoreline.

Last summer, in Calvert County, health officer David Rogers called the four infections there "an insignificant problem," and was reluctant to warn residents. It wasn't until the state issued warnings that county officials decided to issue warnings at beaches. These came after a Bay Journal online report about the cases.

Interviewed for this article, Rogers said that while citizens like Tutman criticized him for not doing enough, others in the public health community complained the postings were overzealous in proportion to the risk.

"We felt that, as a matter of public education, we had to react in some way, so it wouldn't seem to the public that we were doing nothing," Rogers said. He thinks that this year, he may follow Anne Arundel's lead and issue a press release including general warnings before the summer beach season.

Mauro Lanzisera believes health departments ought to do more. Last year, the part-time Broomes Island waterman tripped on his dock as his boat rope got away from him. He jumped into the water to get the boat. Then, knowing the risks of entering the water with an open cut, he showered, washed his cut with peroxide, and put Neosporin on it. He went back out crabbing a bit later.

That night, Lanzisera recalled, "it felt like someone took an ice pick and drove it through my ankle." His wife took him to Calvert Memorial Hospital, where a doctor told him it was a sprain, wrapped it up and sent him home.

The next day, Lanzisera's wife told him his foot "smelled like death." It was the Fourth of July. She took him back to the hospital, where an Air Force doctor happened to be moonlighting for some extra holiday cash.

The doctor had been in Mississippi after Hurricane Katrina. He took one look at Lanzisera's ankle and knew exactly what he saw.

"He told me that I might die, and that I might lose my leg, but it was absolutely guaranteed that I would be in the hospital for many days," Lanzisera said.

Lanzisera was rushed to the University of Maryland Shock Trauma Center, where he immediately underwent surgery.

After nearly one month at Shock Trauma, six surgeries, a month of rehab, intense physical therapy and months of bedrest, Lanzisera can walk again. His employer, Quality Built Homes, stuck with him and kept his job. And the retired fire battalion chief even plans to crab again, but not during July, August or September.

Had the first doctor known the extent of the problem, Lanzisera said, his life might not have been in such jeopardy.

"The state does have an obligation to tell people what this bacteria reacts to," Lanzisera said. "There are a lot of people who come down here with kids, kids who have cuts. They don't need to be afraid, they just need to know."