Flesh-eating bacteria linked to raw oysters may be spreading. Here’s what to know

In recent months, infections with a flesh-eating bacteria have made headlines and spooked raw-oyster lovers around the United States. The culprit? Vibrio — specifically, vibrio vulnificus, and becoming infected with it, a condition called vibriosis, can lead to life-threatening complications.

Some experts are concerned that vibrio vulnificus, which thrives in warm coastal waters, is expanding geographically and could infect more people as water temperatures rise due to climate change.

Vibrio vulnificus infections are rare, especially in the Northeastern U.S., but recent reports of cases and deaths as far north as New England have ignited new warnings from health officials.

On Sep. 1, the U.S. Centers for Disease Control and Prevention issued a health advisory about recent reports of severe vibrio vulnificus infections associated with warming coastal waters.

In July and August, the U.S. experienced above-average coastal sea temperatures and widespread heat waves, per the CDC. During this same period, at least six deaths from vibrio infections were reported in three states along the East Coast.

Florida man dies eating oysters

In August 2022, a Florida man died after eating raw oysters, NBC News reported. At the time, the Florida Department of Health said 26 people had been infected with vibrio vulnificus after eating raw shellfish so far that year, and six of them later died.

Similar incidents have happened this year, including one man from Missouri who died in June. NBC News reported in August that a person in New York and two in Connecticut died from vibriosis associated with wound infections or consuming raw oysters.

Additionally, three deaths due to vibrio in North Carolina prompted state health officials to urge caution around swimming in saltwater or brackish water, according to the North Carolina Department of Health and Human Services.

There’s no need for the public to panic, according to experts, but it’s important to stay informed. What causes vibrio vulnificus, where is it found, and are cases and deaths actually on the rise?

What is vibrio vulnificus?

Vibrio vulnificus is a species in the vibrio group of bacteria, which lives in marine environments. The majority of vibrio strains are harmless, but about a dozen species can cause disease in humans, Salvador Almagro-Moreno, Ph.D., associate professor at the Burnett School of Biomedical Sciences at University of Central Florida, tells TODAY.com. According to the CDC, vibrio vulnificus is one of the most common strains in the U.S.

Vibrio vulnificus is sometimes called flesh-eating bacteria because an infection with it can cause flesh around an open wound to die. People become infected with vibrio vulnificus through exposing an open wound to saltwater or brackish water where the bacteria lives or through eating raw shellfish.

The bacteria are not a result of pollution. “They’ve been there for millions of years. That’s where they live … which makes the option of eradicating them impossible,” says Almagro-Moreno, who directs a laboratory which researches the evolution of vibrio.

Where is vibrio vulnificus found?

Vibrio thrives in warm saltwater or brackish water (a mixture of salt and fresh water). Brackish water can be found in in estuaries, bays, lakes or ponds. In the U.S., vibrio vulnificus is commonly found in waters near the Gulf Coast, such as in Florida, Texas and Louisiana, says Almagro-Moreno.

Most infections occur between May and October, when water temperatures are warmer.

How can you get vibrio, aka vibriosis?

Vibriosis occurs when you’re infected with a vibrio bacteria. There are two main routes of vibrio vulnificus infections, says Almagro-Moreno.

The first is through open wounds — including cuts, scrapes, burns, punctures, surgical incisions and even new tattoos or piercings — which allow the bacteria to enter the body. This may occur while swimming, wading, fishing or walking on the beach, per the CDC.

Vibrio vulnificus may lurk in floodwaters in coastal areas, NBC News previously reported. “Hurricanes facilitate exposure to the bacteria, because when there’s flooding, the bacterium can enter your home, literally,” says Almagro-Moreno, adding that Florida often sees an uptick in cases after severe hurricanes.

The other route of infection for vibrio vulnificus is through consuming raw or undercooked shellfish, namely oysters, says Almagro-Moreno. Vibrio can also spread if a wound or cut comes into contact with raw or undercooked, contaminated seafood.

Many oysters are harvested from the coastal waters where the bacteria lives, per the CDC. Because oysters are filter feeders, they suck up the ocean water along with any vibrio or other germs in it, which then become concentrated in the oyster’s tissues. So, when oysters are eaten raw or undercooked, a person can end up ingesting the bacteria along with their meal.

How common are vibrio infections?

Vibriosis (from all species of vibrio) causes an estimated 80,000 illnesses and about 100 deaths in the U.S. every year, according to the CDC. About 52,000 of these are caused by eating contaminated food, including oysters.

Vibrio parahaemolyticus, which typically causes diarrhea, accounts for the most vibrio infections (about 40%) in the U.S., per the CDC. Infections with vibrio vulnificus are much rarer, with about 150–200 infections reported each year.

Unlike other vibrio species, vibrio vulnificus is primarily transmitted through open wound contact with contaminated water. Only 10% of cases result from eating raw or undercooked shellfish, per the CDC.

Anyone can become infected, according to the CDC, but people with compromised immune systems, particularly those with chronic liver disease, are more likely to get vibriosis.

Symptoms of vibrio vulnificus infection

The symptoms of infection with vibrio vulnificus can start within 24 hours of exposure and progress rapidly, says Almagro-Moreno. Most people infected with vibrio have mild symptoms that last no more than three days, per the CDC.

Ingestion of vibrio bacteria can cause gastrointestinal illness, with symptoms such as:

• Watery diarrhea
• Vomiting
• Abdominal cramps
• Fever
• Nausea

Symptoms of a wound infected with vibrio vulnificus include:

• Fever
• Redness
• Swelling
• Warmth
• Pain
• Pus or discharge that may spread from the wound to surrounding skin

When vibrio vulnificus gets into the bloodstream, it can cause a severe infection with life-threatening complications, says Almagro-Moreno. These include necrotizing fasciitis — aka flesh-eating disease, where the flesh around an open wound dies — as well as septic shock and death.

Symptoms the bacteria are in the bloodstream include:

• Fever
• Chills
• Low blood pressure
• Blistering skin lesions

“Many people with this infection require intensive care or tissue removal, and about one in five people with this infection die — sometimes within a day or two,” a spokesperson for the Enteric Diseases Epidemiology Branch at CDC tells TODAY.com.

A severe infection may require limb amputation or time in the intensive care unit. For mild cases, treatment beyond drinking lots of fluids isn’t usually necessary.

Are vibrio cases and deaths on the rise right now?

It is clear that vibriosis has been increasing in the U.S. in recent decades, according to Almagro-Moreno and recent data.

While the CDC was unable to confirm to TODAY.com whether infections and deaths to due vibrio bacteria rose in 2023, as it’s still waiting for reports from state health departments, CDC surveillance data indicate the incidence of vibriosis increased from 1996 to 2010, according to a study in the journal Clinical Infectious Diseases.

A 2023 report from the CDC’s Foodborne Diseases Active Surveillance Network found the number of reported vibriosis cases increased in 2022 compared to 2016 to 2018. “Many factors likely contributed, including increases in behaviors like travel and dining out after the peak of the COVID-19 pandemic, and increases in the use of diagnostic tests,” the CDC spokesperson said.

The same report also found that, compared to 2016 to 2018, similar percentages of the vibriosis infections during 2022 resulted in hospitalization and death.

There is also mounting evidence that the geographic range of vibrio vulnificus is expanding.

“I think the trend of cases increasing is mostly associated with the ability of the bacteria to expand geographically,” says Almagro-Moreno. “We’re getting the bacteria in more places so there’s a higher percentage of the population that can be exposed.”

In addition to hotspots in the Gulf Coast, infections are becoming more common along the Atlantic coastline, the CDC spokesperson said, and vibrio vulnificus infections in the Eastern U.S. alone increased eight-fold from 1988 to 2018.

Water temperature is a clear factor. “It’s simple: The bacteria cannot live if the water is too cold, so for them to continue expanding up north, the conditions have to be suitable,” says Almagro-Moreno.

He adds that climate change is driving these temperatures up, creating a bigger habitat for the bacteria. The geographic range of vibrio infections has increased north by approximately 48 kilometers per year, per the CDC.

Warmer waters can also cause the bacteria to persist for longer periods of time, the CDC spokesperson said, but more research is needed to understand if rising temperatures will effect the prime season for vibrio, currently May to October.

According to the CDC spokesperson, vibriosis is likely to become more common and emerge in new places in the country. The rise in natural disasters and hurricanes associated with climate change may also increase vibrio exposures, Almagro-Moreno notes.

In its recent advisory, the CDC urged immunocompromised people to exercise caution around coastal water activities and health care professionals to consider vibrio vulnificus as a possible cause of infected wounds that were exposed to coastal waters.

Vibrio prevention

Several steps can reduce the risk of getting sick with vibriosis, according to the CDC. These include:

• Avoid all contact with seawater or brackish water if you have an open wound or breaks in the skin, including new tattoos, piercings and incisions from recent surgeries.
• Cover all wounds with waterproof bandages if contact with seawater or brackish water is a possibility.
• Seek medical attention right away if you notice a wound is becoming infected, especially after exposure to coastal waters.
• Wash hands thoroughly before handling raw shellfish or other seafood.
• Cook all shellfish, including oysters, until it reaches a high enough internal temperature to kill bacteria (145 degrees Fahrenheit).

How to tell if an oyster is bad

Oysters infected with vibrio do not look, taste or smell any different from other oysters, per the CDC. According to the U.S. Food and Drug Administration, eating oysters from “clean waters” or reputable restaurants does not provide protection either.

“That’s a critical problem that we face … how to differentiate (oysters) with the pathogenic bacteria beforehand,” says Almagro-Moreno, adding that vibrio surveillance for recreational and food safety purposes is a growing area of research.

In the meantime, people should be informed, not alarmed, Almagro-Moreno says.