Sick of the cold? Chill March sees return of norovirus Prof Hugh Pennington, emeritus professor of bacteriology at the University of Aberdeen, said: "Normally at this point in the year we might expect the norovirus season to be coming towards an end - especially when it started so early - but it is called the winter vomiting bug for a reason, and we haven't seen much sign of spring." The virus is closely linked with cold weather, although scientists have yet to determine whether this is because of the climate itself, or because it drives people indoors, where they are in closer proximity and more likely to spread disease. Immune systems are also lowered by less exposure to sunshine during winter. Figures from the Health Protection Agency (HPA) show levels of infections rose steadily during the first three weeks of March, and the numbers were expected to rise as laboratory reports are received. Research has shown that spikes in the disease are most likely a week after a cold snap, meaning that the coldest March since 1962 is likely to have exacerbated its spread. HPA laboratory tests confirmed 6,579 cases of norovirus up until March 20, compared with 6,215 at the same point last winter. Estimates for the total population affected are calculated on a ratio of one laboratory case for every 288 cases in which people do not seek medical treatment. Anyone who believes they have the bug is advised: Do not visit your GP surgery or local A&E unit. You will recover without treatment, but you should take plenty of drinks to replace lost fluids. Use NHS Direct's online health and symptom checker to get advice on how to manage your symptoms. Wash hands thoroughly and regularly at all times, but particularly after using the lavatory and before eating. Do not visit people in hospitals or care homes as there is a real risk that you would put vulnerable people at risk. Remember, you remain highly infectious for at least 48 hours after recovery.