The Department of Health is investigating a gastroenteritis outbreak affecting 150 students of a primary school in Western.

Two are in stable condition in hospital while the rest are recovering at home after complaining of vomiting, diarrhoea and abdominal pain. Examinations of some of the students have tested positive for the Norwalk-like virus.

Viral gastroenteritis caused by the virus is usually self-limiting with symptoms of nausea, vomiting, diarrhoea, abdominal pain, low-grade fever and malaise. The symptoms usually last 24 to 48 hours. Viral gastroenteritis is more common in winter months.

Last year there were nine reported outbreaks in primary schools, affecting more than 300 students.

The department issues the Guidelines on Prevention of Communicable Diseases to all child care centres, kindergartens, schools and relevant institutions.

Following the outbreak, officers have provided the school concerned with health advice on viral gastroenteritis and proper disinfection procedures.

The school management carried out thorough disinfection of the premises today and it will continue tomorrow under the supervision of the department.

The infection can be transmitted via contaminated food or water, contact with infected people and contaminated objects.

To prevent viral gastroenteritis, people should:

* wash hands thoroughly before handling food and eating, and after going to the toilet;

* wear gloves while disposing of vomit and faeces, and wash hands afterwards;

* clean and disinfect contaminated area and items promptly and thoroughly with household bleach diluted at a ratio 1 to 49 units of water;

* sick students should rest at home and not go to school;

* maintain good indoor ventilation; and,

* eat only thoroughly-cooked food, particularly seafood and shellfish.

With the approach of the high season for viral gastroenteritis, schools are reminded to watch for students with symptoms and report to the department if an outbreak is suspected.

People can obtain health advice on preventing the virus at the department's website (www.info.gov.hk/dh), or by calling its Central Health Education Unit hotline on 2833 0111.