Vibrio-related infections are rare but serious
Severe illnesses can prove fatal within 48 hours of first contact
Dr. Gregory Buck knows the potential danger posed by Vibrio vulnificus, the marine bacteria responsible so far this year for almost 30 cases of life-threatening infections in Texas and topic of concern among many of the hundreds of thousands of Texans anticipating visiting beaches and bays during the coming July Fourth weekend. It’s his profession.
Buck, associate professor of biology at Texas A&M University-Corpus Christi teaching classes in microbiology, virology, immunology and bacteriology, has spend years studying Vibrio bacteria, including research into Vibrio vulnificus genes’ role in the microbe’s virulence.
He’s quick to acknowledge the potential health risks to those infected by the bacteria and the need for the public to be aware of the pathogen that can, in some cases, prove fatal in as little as 48 hours after exposure. But he’s also keen for Texans to be more fully informed about the bacteria, understanding where it’s most likely to be found, who is most susceptible to becoming infected and the odds of such infections.
“It’s certainly something to be aware of, especially for those most susceptible to infection,” Buck said. “But it’s always been out there, and, for most people, the odds of it causing a problem are very low.”
Vibrio vulnificus is a common bacteria in warm coastal waters, Buck said. A member of a family of bacteria that includes the pathogen causing cholera, vulnificus requires a saline environment to live. But it thrives only in water within a fairly narrow salinity range. And that’s a key to where it’s most likely — and unlikely — to be encountered.
Salinity levels
Vulnificus does best in water with a salinity concentration of between 20 and 40 parts-per-thousand, Buck said. In waters with higher or lower salinity levels, the bacteria struggles to survive. On the Texas coast, especially this year with heavy freshwater runoff pouring into bays, salinity levels in many areas of the bays are far below 20 ppt; much of Galveston Bay this early summer has seen salinity levels below 10 ppt and often below 5 ppt. Expect the bacteria to be rare in those low-salinity waters.
The same applies to waters with very high salinity levels. Hypersaline bays such as Baffin Bay and parts of the Upper and Lower Laguna Madre, where salinity levels regularly exceed 50 ppt and can climb as high as 80 or 90 ppt during a dry summer, are hostile environments for the bacteria. It is worth noting that Vibrio vulnificus infections are almost unheard of from those hyper-saline bays.
Almost all of this year’s 27 reported cases of severe Vibrio-related infections occurred in areas where salinity levels were in the 20-40 ppt range.
Over the past couple of decades, Texas has annually averaged 15-30 reported cases of severe Vibrio vulnificus-caused infections. The majority — more than 80 percent — occur between May and October, the warmest months of the year. The bacteria thrive best during these warmweather months, Buck said.
“Water temperatures from 60 to 86 degrees Fahrenheit are optimum,” he said.
Those also are the months when the largest number of people come in contact with coastal water through swimming, fishing, boating and other activities.
Staying aware
Not all Vibrio-related illnesses are life-threatening. The majority of illnesses are caused by ingesting seafood, usually uncooked oysters, that carry the bacteria. The most common — gastroenteritis — is treatable, although sometimes it can develop into a more serious infection.
Invariably, the most severe cases are triggered by the bacteria entering a victim’s body through an opening in the skin — a wound. It can be something as obvious as cut from brushing against an oyster, a puncture from a hook, a stab from a hardhead catfish fin, a poke from a shrimp’s “horn.” Or it can be an existing wound or even something as simple as a rash; there have been cases where the bacteria found its way into the victim through athlete’s foot or similar relatively minor breaks in the skin.
Once in the skin, the bacteria can cause havoc and do it quickly.
The bacteria produces a severe toxin that destroys tissue. And that tissue destruction can spread rapidly.
“You can almost watch it move up an extremity,” Buck said. Typically, a person suffering a severe infection from vulnificus bacteria sees problems within a few hours of the bacteria entering the body. Redness and swelling around the infection site, fever and blistering quickly developing into sepsis.
In severe cases, the infection and the resulting necrotizing fasciitis can spread so rapidly that it can prove fatal within 48 hours. Extreme measures, including large-scale removal of skin and amputation of limbs, are common medical attempts to stop the spread of the bacteria and its tissue-destroying effects.
Evidence indicates people with compromised immune systems are much more susceptible to Vibrio vulnificus infection than the general population, Buck said.
Those at highest risk
People with liver or kidney disease, diabetes, hepatitis, cancer are at particular risk, Buck said, as are those with hemochromatosis, a condition in which the blood holds much higher levels of iron than normal.
“The bacteria thrive on iron,” he said.
Infectious disease specialists estimate 6-17 percent of the nation’s population has a medical conditions making them especially susceptible to Vibrio vulnificus infection.
Also, men appear much more susceptible to the most severe infections. About 80 percent of the victims of the most severe vulnificus infections are male.
While there’s the possibility of developing a serious, even life-threatening infection through encountering Vibrio vulnificus in Texas coastal waters, the odds of becoming a victim are incredibly small, Buck said.
“The incidence rate is about one in a million,” he said.
‘Not something to ignore’
Those odds show just how unlikely it is someone fishing in a Texas bay or swimming along the beach front will suffer serious health issues from an encounter with this common bacteria. But it doesn’t mean it’s impossible — ask the 27 Texans who have found out otherwise this year.
“It’s not something to ignore,” Buck said. He strongly recommends anyone who develops symptoms suggestive of possible Vibrio vulnificus infection — pain, redness, swelling or blistering around a wound or scratch, fever, etc. — immediately seek medical help and inform the health care worker about exposure to saltwater.
“At the first sign of any problem, get to a doctor,” Buck said, noting waiting a day can be a fatal mistake.
But, he said, it pays for those visiting the coast to put the very low risk of becoming a victim of Vibrio vulnificus in perspective.
“For most people, the most dangerous thing they’ll do is get in their car and drive,” he said.