The last nine of 149 patients who were infected of the norovirus, also known as "stomach flu", have recovered and been discharged from hospital in Changsha, central China's Hunan Province.

The nine, all students, returned to school on Monday, said Peng Hongwei, an official with Changsha City Center for Disease Control.

The 149 students and teaching staff at the middle school affiliated to Hunan Normal University started complaining of vomiting, diarrhea and nausea on March 6.

Experts concluded the school had been hit by an outbreak of norovirus-inflicted, infectious diarrhea.

The patients -- 145 students, two teachers and two other workers -- were treated at the Fourth Hospital in Changsha, and the other 140 were discharged last week.

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.

Local health experts are still trying to establish the source of the infection.

(Xinhua News Agency March 19, 2007)