It seems as if every few years the media becomes fascinated with a few rare illnesses caused by Vibrios, and suddenly every news outlet, blogger and food writer feels compelled to run a story with attention-grabbing headlines that end up killing shellfish markets. If you were reading the news in the summers of 2019 and 2023 you probably noticed a flood of articles about “flesh-eating bacteria.” This is just the sort of click-bait headline that is guaranteed to attract attention and boost ad revenue. Unfortunately, the lazy journalists who posted these articles were also scaring people away from shellfish consumption and marine-related recreational activities. I spent much of both summers trying to respond to these reports and to persuade authors to retract or amend their articles to reflect the facts. But good news is boring and as the saying goes in journalism circles, “If it bleeds, it leads.”

So why do we see these explosions of deceptive reporting? One answer can be traced to a report out of Rutgers in spring 2019 that documented a handful of Vibrio vulnificus  (V.v.) wound infections that were traced to Delaware Bay. Graphic descriptions of disfiguring skin blisters, amputations and life-threatening illnesses were enough to get dozens of news outlets to pick up the story and run with it.

Then in the summer of 2023, three Connecticut residents (two of whom died) and one New York resident (who died) were hospitalized with Vibrio vulnificus  infections. One of the Connecticut patients had eaten oysters from out of state, although it is unclear if that person died. At least two of the three 2023 fatalities had open wounds or cuts that were exposed to warm or brackish waters in Long Island Sound.

In addition to those 2023 cases in the Northeast, three V.v. wound infections in North Carolina resulted in fatalities. All three patients had been exposed to warm, brackish water and had open wounds, and one of the victims also had eaten recreationally-harvested oysters. On September 1, 2023, the U.S. Centers for Disease Control and Prevention (CDC) issued a health advisory about the hazards of swimming with open wounds, cuts or scratches. Naturally, this triggered another round of breathless reporting. The gruesome nature of the victims’ wounds and the lethality of the infections kept the story on the front pages for weeks.

By filing these sensational stories, journalists have sown confusion and caused significant harm to those who make a living from seafood and the businesses surrounding marine recreation. One business owner in New Jersey who rents boats and gear for folks to fish for blue crabs claimed that his business was off by over 50% in the summer of 2023 due to fears driven by reports of flesh-eating bacteria. Resource managers in the mid-Atlantic complained that they were deluged with questions about whether it was safe to go in the water or eat crabs.

What are the facts about Vibrio vulnificus?

Vibrio vulnificus (V.v.) is a naturally-occurring species of bacteria that is ubiquitous in warm, salty or brackish waters. We find it pretty much everywhere on the East and Gulf Coasts when waters are warm, but it has no relation to water pollution. Thankfully V.v. illnesses are extremely rare. The CDC reported a total of 157 cases of V.v. in the U.S. in 2019 (the most recent data), with 66% of cases related to non-foodborne causes (wound infections), and 10% of cases related to foodborne sources (mostly raw or undercooked seafood, including oysters). To be sure, with 157 cases of V.v in a U.S. population of more than 238 million people (2019 numbers), most doctors will never see a case in their entire career.

Most of the infections occur in the immune-compromised population (such as people with liver damage; or who are taking medications that suppress their immune response to treat HIV or cancer, or to prevent transplant rejection). For these individuals the infections can quickly invade the blood (sepsis), and the mortality rate can be as high as 20-40%.

To be accurate, V.v. is not the only species of bacteria known to cause necrotizing fasciitis, or  “flesh-eating disease.” True flesh-eating wound infections are mostly associated with Type A Streptococcus or Staphylococcus aureus bacteria (MRSA). Although septic V.v. infections can cause disfiguring skin blisters requiring surgery or amputation, it is not accurate to lump V.v. in with the much more common strep and staph bacterial infections.

If the news reports had stuck to the facts, it might not have been so bad. Most people would have seen the low rates of infection and concluded that their own risk was minuscule. Hopefully, the immune-compromised population would take appropriate precautions by protecting wounds and scrapes from warm seawater and by avoiding raw shellfish, while healthy folks would go about their lives with little to fear. Unfortunately, these irresponsible journalists did not stop there. Without putting in the clutch, they shifted gears and reported that the CDC estimates there are 80,000 cases of vibriosis a year across the country, effectively lumping a very rare and potentially life-threatening disease (necrotizing fasciiitis) in with all the other types of Vibrios that can cause illness, which though more common, are far less dangerous.

What is vibriosis?

The broad category of vibriosis includes illnesses caused by dozens of pathogenic Vibrio species, such as V. cholera and V. parahaemolyticus. The CDC collects data on all lab-confirmed Vibrio illnesses. In 2019 a total of 2,685 lab-confirmed cases of vibriosis (from all species of Vibrio) occurred nationwide, but because of under-reporting and misdiagnosis, the CDC estimated that 80,000 vibriosis cases occur annually.

What about Vibrio parahaemolyticus?

The most common of the vibriosis pathogens is Vibrio parahaemolyticus (V.p.), which caused 640 confirmed cases in 2019, 78% of which were tagged as foodborne by the CDC.

V.p. prefers seawater (while V.v. is more common in brackish water), but again V.p. is ubiquitous in warm marine waters around the globe. There are hundreds (possibly thousands?) of  benign strains, but several strains have caused significant outbreaks, often sickening dozens at a time.

Most V.p. illnesses are associated with eating raw or undercooked seafood. Since many Vibrios are chitinolytic (they consume the shells of crabs, shrimp, lobster and copepods) we see many V.p. illnesses from handling or consuming raw or undercooked crustaceans. But most cases are associated with the consumption of raw shellfish, and oysters are the chief culprit because they filter the water quite efficiently and can concentrate bacteria as they feed. Oysters are also implicated frequently because consumers like to eat them raw, especially in the summer months.

Most V.p. illnesses cause nasty skin infections or gastroenteritis, but again, for the immune-compromised population V.p. can cause life-threatening septic infections. The CDC reports that in  2019 V.p. illnesses had a 1% mortality rate (7 deaths).

How should we interpret the CDC’s numbers?

First of all, we need to recognize that this is not an exact science. The Cholera and Other Vibrio Illness Surveillance (COVIS) system was initiated by the CDC, FDA, and four Gulf Coast states as a national database for Vibrio in 1989. Most states were voluntarily reporting Vibrio cases in the early 2000s; in 2007 the CDC mandated that all states report vibriosis illnesses.

Vibrios are not easy to culture from fecal samples, so many cases go undiagnosed, and most people don’t bother to go to the hospital for a mild case of gastroenteritis.

Is vibriosis increasing?

The CDC believes the prevalence of vibriosis has been increasing over the past decade, and so is pushing for tighter regulations. With most foodborne illness on the decline, what could be the cause of this perceived increase? Several explanations are possible:

1. States are clearly getting better at complying with reporting requirements that have been mandated since 2007.
2. In recent years hospitals have widely adopted Culture Independent Diagnostic Testing (CIDT). This is a PCR device that detects snippets of DNA or RNA from the most common pathogens in fecal samples. The device is inexpensive and generates results in hours instead of days, meaning that detection is far more common than it was just a few years ago. It is safe to say that the multiplier used by the CDC to estimate total cases based on lab-confirmed cases should be revised downward to reflect this new reality.
3. We know that the frequency of vibriosis cases in New England shot up after the introduction of a new hyper-virulent strain of V.p. in 2012. But we have also seen a doubling of oyster production in the five years pre-COVID, leading to the likelihood that more raw oysters are being consumed, and more often in summer, than ever before. Unfortunately, harvest data is pretty thin so it is tough to make this case.
4. Scientists are linking increases in the spread of vibriosis to climate change, as increasing warming increases the pathogen’s range and lengthens the season. In a paper published in 2022, scientists estimated the economic impacts of vibriosis cases as exacerbated by climate change. They projected that by 2090, increases in sea-surface temperatures could result in a 51% - 108% increase in vibriosis cases annually (relative to the baseline era centered on 1995), costing more than $5.2 billion - $7.3 billion (relative to $2.2 billion in the baseline of 2018 U.S. dollars). This works out to a projected increase of 140% - 234% in health care costs associated with vibriosis.

And so the question remains: Is vibriosis becoming more common or are we just getting better at detection and reporting? With the advent of CIDT there is little doubt that detection is improving. Unfortunately, we have no way of determining whether illness rates per meal are increasing or decreasing. One thing is certain: since the CDC believes illnesses are on the rise, and our industry lies squarely in the cross-hairs, we could see even more proposals to tighten regulations at ISSC meetings going forward.

What can we do?

• Keep ‘em cold. Vibrios love heat, so the single most important thing we can do is to promptly cool down shellfish harvests to stop bacterial growth. We can’t eliminate Vibrios in live shellfish, but if we can keep our shellfish below 50°F we can keep safe shellfish from becoming unsafe.
• Fight back with facts. When you see one of those click-bait articles in the media, push back with facts in the comment section. I can’t do this all by myself!
• Educate the immune-compromised population about the risk of consuming raw shellfish. They should enjoy their shellfish well cooked!
• Support your state and regional shellfish associations. They are coordinating the industry response to the CDC’s regulatory push at ISSC meetings, and they need your support.