The so-called winter vomiting disease, which has affected patients and staff in hospitals and residential homes since the spring, has become "quite a problem" in the hotel sector.
Package tour groups are particularly affected, Dr Margaret O'Sullivan, a public health specialist with the Southern Health Board, said yesterday.
This has also been seen in Britain and the health board is now following British guidelines specific to the hotel industry which have been drawn up in the light of experience there.
Confined areas where large numbers of people congregate, such as buses, are considered breeding grounds for the transfer of the Norwalk-like virus or Small Round Structured Virus (SRSV)which causes the vomiting and diarrhoea, Dr O'Sullivan said.
Also called gastric flu, it was recognised as an increasing problem in the holiday industry and in tourist resorts where people-come and go all the time.
"In the package industry people are on the move a lot, people stay for short periods in various hotels. They are not confined to this region. They are coming into the region and moving out of the region. We are seeing a lot of this virus on the move at the moment," she said.
Since mid-August, the health board has received reports of clusters of cases in the Cork and Kerry region, particularly among holiday-makers, and some hotels have been affected. Six cases were reported in a small number of hotels in Killarney on Wednesday, the board confirmed yesterday.
Staff affected by symptoms are being asked to stay out of work for at least 48 hours until after the symptoms have passed.
Over a week ago, the number of cases reported in Killarney in the course of 10 days reached 36. The disease was felt to be on the wane at the time, with just one case reported, but it has since returned to the same small number of hotels, it appears.
The health board's outbreak control team, which is made up of of area medical officers, environmental health officers and specialists in public health medicine, have been advising the hotels.
The disease is highly infectious and spreads easily, the health board stressed in a statement. Food too may be contaminated.
The health board advises strict personal hygiene, especially hand-washing, as well as cleaning and disinfecting toilets and tour buses with bleach where there has been an outbreak.
Soiled soft furnishings should be machine-washed or steam-cleaned.
"People working in the tourist and other service industries should immediately report sickness to their employer," the statement issued by the board advised.
The current outbreak was not confined to Kerry - similar outbreaks have occurred in other parts of the country, the health board said.
A fact sheet issued by the National Disease Surveillance Centre is available on their website at www.ndsc.ie.