(CNN) -- The U.S. government warned consumers Sunday to avoid oysters from San Antonio Bay in Texas after investigators found the oysters caused a highly contagious virus.

Consumers who bought San Antonio Bay-harvested oysters on or after November 16 should throw them away, the Food and Drug Administration announced. The agency also advised restaurant managers and grocers not to serve or sell the Texas oysters.

About a dozen cases of norovirus-related illnesses in North Carolina and South Carolina were "definitely linked" to oysters recently harvested from the San Antonio Bay, FDA spokeswoman Rita Chappelle told CNN.

Texas' health department has already recalled all oysters harvested from the bay between November 16 and November 25, the health department said in a statement on its Web site. San Antonio Bay has also been closed to commercial oyster harvesting, the statement said.

Texas authorities are still investigating how the oysters were contaminated and where they were distributed, Chappelle said.

Noroviruses cause gastroenteritis, also known as the stomach flu. They are highly contagious, according to the Centers for Disease Control and Prevention. Aside from contracting the virus from food or drink, one can become ill by touching contaminated surfaces and then their mouth, or by coming into direct contact with an infected individual.

Symptoms associated with the virus include nausea, vomiting, diarrhea and stomach cramping. Affected individuals often experience low-grade fever, chills, headache, muscle aches and fatigue. The illness typically lasts one to two days according to the CDC.

Anyone who ate the now-recalled oysters and who are now showing symptoms of norovirus should see a doctor and contact the local health department.

CNN's Khadijah Rentas contributed to this report