Most people who become infected get rid of the virus within 6 months, but it can cause cirrhosis (scarring) of the liver, liver cancer, liver failure, and even death. Not everyone who tests positive goes on to develop any symptoms, although they could still be spreading the disease.

"All the seven students we sent away are Hepatitis-B virus carriers in a contagious period," Sun Xiaomei, an administrative official from the No 67 Middle School told China Daily yesterday.

"We made the decision when considering a safe environment for our other 900-plus students, including 400 that board," Sun continued.

Yin Xiuqin, from the No 15 Middle School, showed reporters a paper released in March by the Urumqi education department. It said students can be told to leave school if they have "chronically contagious diseases in a spreading period, all kinds of epidemic diseases in acute conditions and abnormal liver functions."

"We are doing things according to the rules," Yin said.

An official with the Urumqi Education Bureau who was reluctant to give his name told local media on Monday: "We have proved their cases may cause an epidemic after DNA tests. We had to tell them to leave school."

Zhang Yuexin, a senior expert from the Xinjiang Liver Disease Centre, disagreed, telling the Nanfang Daily: "There is nothing wrong with their liver functions. Viruses are duplicating inside their bodies, but do not show they are in an acute period."

"What the schools have done is not legal. Even if the students are Hepatitis-B virus carriers, they still have the right to a normal school life," a local lawyer named Zhang Yuanxin told China Daily.

China has launched a nationwide campaign calling on people not to take a biased attitude towards people carrying the Hepatitis-B virus, said Mao from the Ministry of Health.

The number of Hepatitis-B patients has become a major public health issue, sources from the ministry said.

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