Like gambling? Eat raw oysters

Hepatitis A and Vibrio vulnificus are two potential dangers.

If you're considering sampling local seafood on your next coastal vacation, you might want to steer clear of raw oysters, said Thomas A. Moore, MD, FACP, chair of infectious diseases at Oschner Medical Center in New Orleans, at a talk during the Hospital Medicine precourse at Internal Medicine 2012.

“There are many reasons not to eat them. Hepatitis A is one; another is toxoplasmosis. The biggest risk factor for acquiring this parasitic infection is the consumption of raw oysters,” Dr. Moore said. “It's like Russian roulette. Eating [raw oysters] is OK now and then, but if you go on a bender, you're gonna get it,” he said.

Thomas A Moore MD FACP Photo by Kevin Berne
Thomas A. Moore, MD, FACP. Photo by Kevin Berne.

Another risk—and the subject of a portion of his talk—is Vibrio vulnificus. The organism is part of the normal marine flora, especially oysters, and tends to cause disease in warmer months. With a mortality rate of 50%, it accounts for 90% of all seafood-related U.S. deaths. A few years ago, The Sunday Times (of London) food critic Michael Winner nearly lost his leg from contracting the illness after eating a bad oyster, Dr. Moore noted.

Cases related to V. vulnificus have been increasing along the Gulf Coast, “perhaps due to global warming,” Dr. Moore said.

Refraining from eating the raw mollusks won't entirely protect you from the skin and soft tissue infection caused by the organism, though, as it can be contracted from nonfoodborne exposure too, he said. Still, 90% of patients who get ill from V. vulnificus report having eaten oysters within the previous seven days, he noted.

Typically, the illness starts with abrupt onset of rigors, then fever and prostration. This is followed by hypotension in a third of cases. In 75% of cases, metastatic skin lesions develop with 36 hours of initial symptom onset, usually on the extremities, with the legs being more common than the arms. Leukopenia and thrombocytopenia are also common, but not universal, he said.

Vibrio vulnificus is primarily associated with severe, distinctive soft tissue infection and/or septicemia,” Dr. Moore said. “What you usually don't see is diarrhea; it invades the bloodstream without causing [gastrointestinal] symptoms.”

Patients typically develop sepsis within 16 hours of symptoms and cellulitis somewhere between four hours and four days (the mean time is 12 hours), he said.

Physicians should consider V. vulnificus when a patient has septicemia associated with necrotizing skin lesions; is immunocompromised, as with liver disease; and has ingested or was exposed to oysters and/or salt water in the past one to three days.

If you do suspect V. vulnificus, be sure to alert the lab that is performing tests, as it may otherwise be missed. Only 25% of labs in Gulf Coast states routinely culture for the bacteria, he said.

In treating complicated skin and soft tissue infection due to V. vulnificus, the best option is tetracycline. Other good options include ceftriaxone and ciprofloxacin.

Patients with cellulitis from V. vulnificus respond well to antibiotics, but early diagnosis is critical as the condition progresses rapidly, Dr. Moore added. Early surgical consultation is also advised. “These patients often need early and aggressive debridement,” he said.

Patients who have developed bacteremia don't respond as well to treatment, though starting antibiotics within 24 hours of the onset of symptoms does help lower mortality for these folks, he said.

Those who still want to ingest raw oysters after learning the potential consequences can lower their chances of getting sick by using tabasco, noted Dr. Moore. Research suggests the vinegar in the condiment inhibits the growth of V. vulnificus, so the higher the vinegar content of your chosen brand, the better, he said.

Oh, and cooked oysters? Totally safe, he said.