DIX HILLS, N.Y. - A mysterious gastrointestinal virus at a Dix Hills assisted living facility has sent at least four residents to the hospital, canceled all activities and forced residents to stay in their rooms, Suffolk authorities and facility officials said Sunday.

Residents of Sunrise Assisted Living Incorporated" id="ORCRP014679">Sunrise Assisted Living on Deer Park Avenue began experiencing symptoms of extreme nausea and diarrhea sometime last week, resulting in four hospitalizations this weekend, officials said.

Two residents are at Good Samaritan Hospital Medical Center in West Islip" id="PLGEO0000764NY">West Islip and two are at Huntington Hospital, said Grace Kelly" id="PECLB002738">Grace Kelly-McGovern, a spokeswoman for the Suffolk Department of Health Services.

The patients were not identified but were reported to be in stable condition.

"The patients are doing fine," Kelly-McGovern said. "We're monitoring the situation and we're in touch with both the hospital and Sunrise."

The nature of the virus was unknown, officials said. Sara Krueger, a spokeswoman for Sunrise, said: "We have no confirmed diagnosis of Norwalk virus," a common disease in health care facilities spread through food and human contact.

To stop the virus, Krueger said Sunrise staff cleaned the facility with disinfectant, canceled all group activities such as nightly movies, asked residents to stay in their apartments and served meals in their rooms on paper plates with plastic utensils.

Krueger said the safety measures will remain until it is determined the virus is no longer active.

Sunrise employees wore surgical masks Sunday, which residents and visiting family members said was unusual. Krueger said the masks were not related to the virus, but would not comment on whether it was a common practice for staff to wear them.

Relatives of residents said facility staff told them as many as 20 residents in the 80-resident facility had become sick in the last week. Krueger would not say how many were ill but said "20 sounds high to me."

Inside the facility, the common areas were empty and silent, except for staff. They appeared to keep their masks on in the facility, taking them off during breaks outside.

Johanna Schwartz, of East Northport, said she was concerned about the health of her mother, Celia Bisom-Israel, 96. "It's really eerie in there," Schwartz said, adding that employees told her that the illnesses started Tuesday. "Residents have been throwing up and going to the hospital. It's very strange."

Krueger said the facility contacted Suffolk Health Services about the outbreak yesterday. Kelly-McGovern said the law is unclear about how soon assisted living facilities must report viral outbreaks.

Krueger said other nursing homes and assisted living facilities were facing similar issues, though she declined to name them. "At this time of the year this is not an unusual occurrence for any environment like this," Krueger said. "We feel like we're taking every precaution."