Raising a red flag over oysters harvested in southeastern Connecticut last week, the U.S. Food and Drug Administration has issued an alert, advising consumers not to eat the oysters, which may be contaminated, and restaurants and food retailers not to serve or sell them.

The alert came after the Connecticut Department of Agriculture pursued a “precautionary closure” Aug. 30 of certain shellfish-growing waters off Groton and Stonington due to possible sewage contamination.

In a statement released Wednesday, the department said shellfishing industry members voluntarily recalled all oysters harvested from the waters from Aug. 28 through Aug. 30 and distributed throughout Connecticut and in other states.

No illnesses linked to the oysters have been reported, and all oysters that had not been consumed were destroyed or returned to the growing area, the department said.

The precautionary closure was undertaken “in an abundance of caution” following routine water and shellfish monitoring that produced results “outside the normal parameters of the area ...,” it said.

The department said it is working with the shellfish industry, towns, local health departments and sewer departments to determine the potential source of contamination. In the meantime, it said, the shellfishing area will remain closed to harvest until the source of the potential contamination is located and repaired.

“The area will be reopened following the national guidelines as set forth by the National Shellfish Sanitation Program Model Ordinance, or NSSP-MO, and the collection of acceptable sample results,” the department said.

In its alert, the FDA said it notified restaurants and food retailers in Connecticut, Massachusetts, New York, Pennsylvania and Virginia that had purchased oysters harvested from what’s known as the Groton Approved shellfishing area from Aug. 28 through Aug. 30. The potentially contaminated oysters may have been distributed beyond the five Northeast states, the FDA said.

The alert also pertained to consumers who purchased and may have eaten the oysters.

Contaminated oysters can cause illness, especially if eaten raw, particularly among people with compromised immune systems, according to the FDA. Food contaminated with pathogens may look, smell, and taste normal.

People who have eaten oysters and are experiencing food poisoning symptoms such as diarrhea, stomach pain or cramps, nausea, vomiting, or fever should contact their health care provider, who should report their symptoms to their local health department.

The agriculture department said its imposition of a precautionary closure has no relation to three Vibrio vulnificus wound infection cases reported in Connecticut in August. Two of the cases reported to the state Department of Public Health were not associated with seafood while the third involved a Connecticut resident who consumed raw oysters at an out-of-state establishment. The oysters were not harvested from Long Island Sound.

Connecticut shellfish have never been linked to a Vibrio vulnificus infection, according to the agriculture department.

b.hallenbeck@theday.com