Bird flu case found in China city

China has reported its first case of bird flu for 18 months, in the major southern city of Shenzhen.

Preliminary tests on a 39-year-old man admitted to hospital with pneumonia proved positive for the virus.

Postive tests on a dead market chicken last week prompted nearby Hong Kong's government to issue an alert.

The island's authorities culled 17,000 chickens after three birds were confirmed to have died from the H5N1 bird flu strain.

It also banned imports and the sale of live chickens for three weeks after the infected chicken carcass was found at a wholesale market.

But it was not clear whether the chicken came from a local farm or was imported.

Meanwhile, the World Health Organization has expressed deep concern about the way research was being carried out on the H5N1 virus, which can be fatal if transmitted to humans.

Such work carried significant risks and must be tightly controlled, said the WHO.

Scientists in the Netherlands and the US said last week they had discovered ways in which the virus might mutate so it can spread more easily to - and between - humans and other mammals.

The US government has asked the scientists not to publish full details, in case the information is used to produce a biological weapon.

The Shenzhen patient had not been in contact with poultry, nor travelled recently, China's Ministry of Health told Hong Kong health authorities.

He remains in critical condition, having been admitted to hospital with severe pneumonia four days after developing symptoms on 21 December.

In November 2010, a 59-year-old woman was isolated with bird flu but survived in Hong Kong's first case in Hong Kong for seven years.

The World Health Organization says bird flu has killed 331 people since 2003.

The virus had been eliminated from most of the 63 countries infected at its 2006 peak, which saw 4,000 outbreaks across the globe, but remains endemic in Bangladesh, China, Egypt, India, Indonesia and Vietnam.

Hong Kong is quick to take action against infectious diseases after an outbreak of the deadly respiratory disease SARS in 2003 killed 300 people in the city and a further 500 worldwide.

In 2009, 300 people were placed under quarantine at a Hong Kong hotel after a guest contracted swine flu.

China's Ministry of Agriculture warned last month that the bird flu virus seemed to exist widely in the poultry markets of mainland China, particularly in the south.