The patients, which include 145 students, two teachers and two other staff members at the school, are being treated at the Fourth Hospital in Changsha, capital of the province, according to the department.

The hospital has organized a team of 19 doctors to provide treatment to the patients, sources with the department said.

The first norovirus infection at the school occurred on March 6, when a 16-year-old girl suffered symptoms of vomiting, diarrhea and nausea, according to the provincial disease prevention and control center.

The school, which has 5,225 students and more than 400 teachers and staff, has stopped supplying water from water coolers and tap water. The school has also cleaned the water boilers, pipes and pools, and is disinfecting buildings and the school environment on a regular basis.

The local disease prevention and control authority is investigating the source of infection.

The norovirus is one of the most common gastrointestinal viruses affecting humans. Its symptoms include nausea, diarrhea, vomiting and abdominal cramps. Symptoms usually appear within 24 to 48 hours of exposure, and typically last for one to three days.

In the fall of 2006, there were massive outbreaks of norovirus infections in Japan, Singapore and Italy, with 357,600 people contracting the virus in less than two months.