Norovirus: Big jump in number of cases of bug in Wales 20 December 2012 Last updated at 18:55 New figures show a big jump in the number of cases of the winter vomiting bug in Wales compared to last year. Wards in hospitals around the country remain closed to new admissions as norovirus continues to cause problems. There have been 557 confirmed cases so far in 2012, compared to 334 in 2011 - a 66% increase - says Public Health Wales. But with many sufferers choosing not to see a doctor, officials say the true figure could be over 150,000. Dr Marion Lyons, director of health protection for Public Health Wales, said numbers varied each year but the virus seemed to have "hit early" this time. If you take an example of a child vomiting in a school hallway, no matter how good the cleaning is, you can still identify the virus a week later on the surfaces End Quote Dr Marion Lyons Public Health Wales "Occasionally we get outbreaks in the summer as well - we had one a couple of summers ago - but this time of year we do now see quite a lot of norovirus circulating," she said. It's just a feature of the virus, it's a common virus. It's easily transmitted from person to person. If you take an example of a child vomiting in a school hallway, no matter how good the cleaning is, you can still identify the virus a week later on the surfaces. You only need a little of the virus to make other people ill which is why we see so much of it because it's so easy to spread and because it likes the environment in which we live and it can last on the surface. The picture across Wales sees: Four wards remain shut at Prince Charles Hospital in Merthyr Tydfil Two wards are closed to new admissions at the Royal Glamorgan Hospital in Llantrisant The University Hospital of Wales in Cardiff has six wards closed The University Hospital Llandough in the Vale of Glamorgan has two wards shut. 35 people were taken ill in four hospitals across north Wales on Monday and two wards are still shut at Ysbyty Gwynedd, Bangor. Health officials say the situation is improving but people with symptoms were being advised to stay away. Betsi Cadwaladr University Health Board was urging visitors with diarrhoea and vomiting not to go to hospital until 48 hours had passed. Norovirus is highly contagious and involves a sudden onset of vomiting and diarrhoea, with possible temperature, headache and stomach cramps. Plenty of fluids The illness usually lasts one or two days and there are no long-term effects. Dr Lyons said it was important for people with symptoms to take care not to spread the bug. "We're asking these people if they are unwell and they think it's norovirus because of the symptoms and the short duration of them, that they don't attend A&E departments or their GP practice," she said. If they need to see a GP, they should ring in the first instance. The important thing is they take plenty of fluids so they don't become dehydrated.