The Gulf Coast has seen a rise in infections caused by Vibrio vulnificus, a deadly pathogen found in warm saltwater and raw shellfish known for its ability to rapidly infect and destroy skin and tissue.
So far this year, the bacteria has been linked to over 70 infections and nine deaths across Louisiana, Florida, Alabama, Mississippi and Texas. Louisiana accounts for a disproportionate share of the cases, with 20 infections and four deaths. In comparison, the state averaged just seven cases and one death per year over the past decade.
Experts point to several factors fueling the recent increase, including rising water temperatures and storm runoff that provides nutrients for bacterial growth. While the bacterium can sometimes enter the body through eating raw or undercooked seafood, the Louisiana Department of Health reports that three-quarters of recent infections involved wounds or other direct water exposure.
Ideal conditions
Vibrio bacteria flourish in warm, brackish waters — conditions that are common during the summer months. After heavy rains and storms, nutrients like phosphorus and nitrogen wash into coastal waters, helping the bacteria multiply, said Tiong Aw, a public health microbiologist and professor at Tulane University.
“All these create an ideal condition for Vibrio to grow and survive,” Aw said.
There are dozens of types of Vibrio bacteria, and they can live in temperatures as low as 50 degrees. But they especially like the warm conditions of the Gulf.
A study published in the Journal of Climate found that water temperatures in the Gulf have risen at twice the rate of global ocean temperatures between 1970 and 2020.
“As the oceans have gotten warmer in recent years, it’s not surprising that cases are increasing,” said Dr. David Mushatt, an infectious disease expert at Tulane University. “Temperature and salt content are what these bacteria like.”
A dangerous infection
Vibrio vulnificus enters the body either through an open wound exposed to contaminated water or by consuming raw shellfish.
Eating raw or undercooked contaminated oysters causes gastrointestinal illness and, in severe cases, a bloodstream infection. That form is not a skin-destroying infection, but it can be life-threatening.
Infection can also occur when Vibrio vulnificus gains access through a break in the skin. Someone shucking raw oysters with a cut, for example, can be exposed if the bacteria invade the wound. It can also enter through injuries sustained in or near the water, such as scraping a leg on a boat, or from any existing wound that comes into contact with contaminated seawater.
Once inside, it multiplies rapidly and releases toxins that kill cells and break down tissue, causing severe damage.
Vibrio vulnificus is a “rare but very serious infection,” said Dr. Norman Beatty, an associate professor of medicine at the University of Florida. Most cuts exposed to seawater will heal normally, he said, but certain warning signs can signal the infection has taken hold.
The first hallmark sign is the appearance of blisters, known as bullae, near the infected wound, and a rapid onset of swelling and redness, Beatty said.
Often, a delay in getting to a doctor who could prescribe antibiotics allows the infection to progress, sometimes requiring surgical removal of infected tissue or even amputation, said Beatty. Severe cases can lead to sepsis and septic shock, which can be fatal.
If you get a cut while in the water, Mushatt suggested cleaning it right away with hydrogen peroxide and antibiotic ointment. But don’t wait if the wound starts turning red, swelling or oozing pus.
“This can progress over hours,” Mushatt said.
Putting off going to the emergency room until your vacation is over is not the right choice. Even a three-hour drive back home from the beach could make a difference in the outcome.
“You wouldn’t want to wait that long,” said Mushatt, who recommended seeking care at a local ER.
People with liver disease, diabetes or weakened immune systems should be especially cautious. “For these individuals, the threshold to seek care is even lower,” Dr. Mushatt added.
Small number linked to raw oysters
Only a small number of recent infections have been linked to eating raw oysters, according to LDH, and no single harvesting area has been identified as a source.
Evelyn Watts, a seafood extension specialist at LSU AgCenter, emphasized that eating raw shellfish always carries some risk, especially from April through October when the bacteria is most active. She advised consumers to look for oysters labeled safe for raw consumption.
Certain groups, including pregnant people, older adults, those with weakened immune systems, and individuals with liver disease, diabetes, kidney disease, or undergoing chemotherapy or other immunosuppressive treatments, should avoid raw shellfish altogether to reduce their risk of serious infection.
Currently, there is no specific state or federal program testing coastal waters for Vibrio vulnificus, said Aw. However, Aw’s lab has been monitoring Lake Pontchartrain for the last year and found the bacteria present year-round, with higher levels during summer when water temperatures reach about 86 degrees Fahrenheit.
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