Sunday, April 16, 2006

Oysters on the half-shell, long a treat for seafood lovers, have become an enemy of public health officials, who point to a continuing rise in human infections traced to the mollusks.

There has been a “sustained increase in incidence of [vibrio],” a bacteria primarily transmitted to humans who consume oysters that have not been thoroughly cooked, according to a report published in the current issue of the federal Centers for Disease Control and Prevention’s Morbidity & Mortality Weekly Report (MMWR).

“Additional efforts are needed to prevent [vibrio] infections, most of which can be prevented by not eating raw or undercooked oysters,” the report’s authors conclude.

The analysis found that incidence of vibrio-induced human illnesses climbed 41 percent between 1996 and 2005. The data was collected through the CDC’s FoodNet program, which gathers data from 10 U.S. states about diseases caused by pathogens commonly transmitted through food.

From 1996 to 2005, the so-called FoodNet surveillance population, which was the basis of this report, rose from 14.2 million people in five states to 44.5 million people in 10 states, including Maryland. At this time, it represents 15 percent of the U.S. population.

“Overall, FoodNet is a very good representative sample of the nation,” said Dr. Ezra Barzilay, a medical epidemiologist in the CDC’s Epidemic Intelligence Service and an author of the report.

However, the total number of laboratory-confirmed cases of human foodborne infections reported to FoodNet in 2005 — 16,614 — actually seems quite low based on earlier published CDC national research that estimated they caused an average of 14 million illnesses and approximately 5,000 deaths each year. The earlier findings were based on results of at least 11 national surveys, selected published reports, and data reported to the CDC from 1988 to 1997.

And while FoodNet found only 109 human vibrio infections in 10 states in 2005, the previous research, published seven years ago, found nearly 8,000 throughout the country, of which about 5,000 were foodborne.

Another study by University of Alabama researchers, published earlier this year, discussed an “increasing number” of infections among people who ate oysters harvested from the Gulf of Mexico.

“A lot of people like to eat oysters, and a lot of vibrio disease is caused by eating them,” Dr. Barzilay said. “So it’s important for people at high risk, such as those with liver conditions, low stomach acid, and those with weakened immune systems and chronic illnesses to avoid them.”

Even with the data from FoodNet, Dr. Barzilay said it is apparent vibrio infections from oysters are a “serious problem.”

“The relative rate of [foodborne] vibrio infections has never been low, and every year since 2000, we have seen increases in the 40 [percent] to 50 percent range,” the federal researcher said.

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