HEALTH chiefs in York launched an investigation after a group of friends fell ill with a highly-contagious stomach bug.

The 20 people fell sick following a day out at York Races - but environmental health officers today said their discomfort was down to the Norwalk virus.

The virus, which causes sickness, vomiting and diarrhoea, is not a form of food poisoning, and is predominantly spread by the air through close contact.

The group shared a box together during an outing on Friday, October 7, during the last meeting of the season.

City of York Council's food safety team investigated the incident, which James Brennan, of York Racecourse, said was taken very seriously.

The Norwalk virus is often seen on hospital wards and symptoms usually last about 24 hours or more - but sufferers remain infectious for a couple of days afterwards.

Mr Brennan, racecourse marketing manager, said "best practice" at Knavesmire was immediately brought into effect following the reports.

"Environmental health has confirmed that the illness was caused by a virus and was not related to the food here," he said.

"It is very unfortunate for those people and we would wish them a speedy recovery. It is also unfortunate that anyone's memory of the race day is understandably affected by these events the day afterwards.

"It is important to be clear that the issue was, and has been proven to be, down to a virus. It seems to be one of those unfortunate things that just happens."

Colin Rumford, the council's head of environmental health and trading standards, said: "The council's food safety team investigated an outbreak of illness amongst a small number of people who attended a function at York Racecourse. Tests have confirmed it was the Norwalk virus, but we are unable to say how it was communicated and passed around."

Updated: 09:27 Saturday, October 15, 2005