To help prevent the spread of the highly contagious virus, the government agency urges the public to be vigilant about hand washing -- especially before preparing and eating food, the BBC reported.
Norovirus, also known as viral gastroenteritis, usually has an acute onset -- nausea, vomiting and diarrhea -- and can last 12 hours or as much as 10 days. People can also have severe cramps or pain -- sometimes to the point of crippling. Most people get better quickly, but the very young and the old can get complications and it can be fatal.
Dr. Lorraine Doherty of the Public Health Agency says a number of cases have been reported in Northern Ireland hospitals. Since last winter many hospitals and nursing homes have had an outbreak of this stomach flu and some wards were closed to prevent further spread virus.
"The only treatment is to stay at home, rest, take plenty of fluids, and to reduce contact with others, both in the home and at work," Doherty said. "It is very important for people who have symptoms of illness not to visit hospitals or their primary care physicians."