Durham, N.C. — The Durham County Environmental Health Division on Monday was investigating an outbreak of gastrointestinal illnesses at a local retirement home, officials said.

A number of residents at the Emerald Pond Retirement Community, off Pickett Road west of U.S. Highway 15-501, have become sick in recent days, and officials were trying to determine whether the illnesses resulted from a virus or food-borne bacteria.

Investigators were collecting stool samples and were distributing questionnaires to residents Monday to begin pinpointing the cause of the outbreak.

“To date, the causes of these illnesses are currently unknown,” Gayle Harris, director of the Durham County Health Department, said in a statement. “However, several outbreaks of norovirus infections have been reported across the state in the past couple of months.”

Viral gastroenteritis, also known as stomach flu, includes the main symptoms of watery diarrhea and vomiting. Sick people might also have headache, fever, and abdominal cramps or stomach ache.

Symptoms usually begin one to two days following infection and could last for one to 10 days, depending on which virus causes the illness. This illness doesn't cause serious long-term consequences in most healthy people, but infants, young children, the elderly and people whose immune systems are compromised are at risk for dehydration from loss of fluids, officials said.