The hepatitis A virus (HAV) can remain in live oysters much longer than expected, according to a study reported in the February issue of the Journal of Food Protection.
Researchers David Kingsley and Gary Richards of the U.S. Department of Agriculture's Agricultural Research Service in Dover, Del., sought to determine how long the HAV contamination could persist within oysters after they had been placed in clean seawater.
"The results were surprising even to us," Kingsley told Medical Week, noting that virus capable of infecting cells persisted in oysters as long as four weeks after overnight contamination, while genetic material of the virus was found as long as six weeks after contamination.
According to Kingsley, these persistence times are much longer than the current three-day cleansing period. These persistence periods are also longer than those used for relaying, a process that involves moving wild oysters to clean waters for a minimum of three days to a couple of weeks depending on state regulations.
According to Kingsley, the long persistence time could suggest that the HAV has some special means of resisting the digestive processes of the oyster.
According to Centers for Disease Control and Prevention estimates, 83,000 cases of hepatitis A illness occur each year in the United States with about 5 percent of them being food-borne.
Although hepatitis A outbreaks have historically been associated with oysters, Kingsley said hepatitis A illnesses associated with oyster consumption are not more frequent because the waters in which they are harvested are tested regularly for fecal bacteria.
Other studies geared toward identifying alternative means of eliminating or inactivating fecal virus such as HAV within shellfish meats are ongoing within the laboratory.
Other sources: Journal of Food Protection, 2003 Feb;66(2):331-4