Claire O'Connell looks at the moves being made to ascertain how the winter vomiting bug, which has already broken out several times this year, is spread.
Finally, some good news for chickens about a virus. Researchers at University College Dublin suspected late last year that poultry might harbour winter vomiting virus strains that could affect humans, but further research by the same group has put the birds in the clear.
Instead, experts say that the main transmission routes for the highly infectious winter vomiting bug are from person to person, through the air or via infected food handlers or surfaces and while outbreaks cannot be prevented, they can be controlled through prompt intervention measures.
Winter vomiting disease is caused by norovirus, which affects around one in 100 people each year.
According to provisional information from the Health Protection Surveillance Centre (HPSC), last year saw around 58 separate outbreaks of norovirus in Ireland and this year so far cases have been reported in hospitals in the midlands and east.
The infection causes self-limiting symptoms of gastroenteritis such as abdominal pain, nausea, diarrhoea and sometimes sudden and projectile vomiting.
The unpleasant symptoms appear rapidly and can last for one to three days.
The hardy virus usually enters the body through the mouth and makes its way to the lining of the gut where it reproduces.
Winter vomiting disease is highly contagious and requires only around 10 norovirus particles for infection.
With around 30 million virus particles shed through a single vomiting episode, abundant particles can remain on surfaces such as clothes, taps and carpets for several weeks.
To find out whether norovirus strains circulate among animals and could contribute to human disease, researchers at UCD's Centre for Food Safety used a sensitive test called RT-PCR, which detects specific strands of genetic material and increases their amounts to more readily detectable levels, to screen beef, pork, sheep meat and chicken for norovirus.
Preliminary results suggested that chicken might harbour genetic material contained in norovirus, says Dr Paul Whyte, a lecturer in veterinary public health and food safety at UCD, but subsequent investigations found no norovirus in the poultry samples.
"The chickens are innocent," he says.
However, food may still act as a vehicle for transmission of norovirus if infected persons handle it, says Dr Paul McKeown, a specialist in public health medicine with the HPSC.
Rather than the germ occurring within the food itself, contaminating norovirus particles on the handler's fingertips or on surfaces where the food is prepared may be transferred to the food and be transmitted to the consumer, he says.
To illustrate, McKeown describes recent cases in the Netherlands and in Ireland where outbreaks of winter vomiting disease originated from a single food handler.
"There was also a large outbreak in the United States about 10 years ago where one man vomited into a sink and washed his hands. He then went on to prepare food and managed to make 3,000 people ill," he says.
The HPSC works with the National Virus Reference Laboratory (NVRL) to monitor circulating strains of the genetically changeable norovirus in Ireland and links into a European surveillance network.
The NVRL tests faecal samples using RT-PCR and electron microscopy.
The time-pattern of occurrence has changed in recent years, says NVRL assistant director Dr Jeff Connell. "It was seasonal at one time but less so now - you get it all the year round now," he says, adding that the peak still occurs in winter.
"You get busy years and quiet years," according to the HPSC's McKeown, who says that 2004 and 2005 were busy years for outbreaks."You can't stop outbreaks," he says.
"Norovirus is a community infection that becomes concentrated where people congregate."
However, while norovirus is not eradicable, McKeown says that outbreaks are quite controllable and he is pleased to see that recent outbreaks have tended to be less severe.
He credits early, rapid response to an outbreak as the key to controlling its extent.
Simple but effective measures include early communication to others about cases of the illness and immediate cleaning and decontamination where there has been soiling.
He advises using 0.1 per cent bleach or a steam cleaner (over 60 degrees centigrade) to disinfect a wide area around vomit, explaining that a mist of expelled virus can travel six to 10 feet either side of the vomit itself.
He adds that ordinary washing with soap and disinfectant won't destroy the virus.
According to the HPSC, to help avoid spreading the virus individuals should also wash their hands scrupulously after using the toilet, vomiting or tending to an infected person and should throw away any uncovered food that was in an area where someone vomited.
People who have been ill with vomiting or diarrhoea should also avoid going back into the workplace for two to three days after symptoms have resolved because they may still be infectious.