Young children and elderly people suffering chronic diseases will be susceptible to acute diarrhoea when another cold spell strikes at the weekend, a doctor warned yesterday. Acute diarrhoea is a symptom of gastroenteritis, or stomach flu, a condition that can be caused by the norovirus and rotavirus. Patients were 25 per cent more likely to suffer from gastroenteritis during cold weather, said Owen Tsang Tak-yin of Princess Margaret Hospital. The Hospital Authority's Kowloon West cluster recorded more than 300 norovirus-positive cases last year, while Dr Tsang said an average of more than 3,000 children a year could be admitted to hospitals as a result of rotavirus infections. Children younger than five and elderly people with chronic diseases should pay extra attention if they experience diarrhoea or vomiting, the two major symptoms of the norovirus infection. Elderly chronic patients could die as their condition might be complicated by the norovirus, Dr Tsang said. He said noroviruses were versatile and could survive in freezing conditions as well as temperatures of up to 60 degrees Celsius, and patients did not develop long-term immunity after a first infection. Over 39 per cent of norovirus infections were transmitted by food, while 12 per cent was a result of human interaction, he said. But the virus could be sufficiently eliminated by cleaning surfaces with water and disinfectant bleach at a ratio of 1:99, Dr Tsang said. A healthy person should get well in two to three days. 'Even though the virus is versatile, we can control it if we remember to do the basics, such as washing our hands frequently.' Dr Tsang said hospitals had taken measures to prevent an outbreak, including sending e-mail alerts and holding educational talks for staff.