Hong Kong ( CNN ) -- NEW : 13 dead from a total of 60 cases of bird flu in China , authorities say . Comment: H7N9 was never known to infect people until last month . Cases of the virus have now spread to central and northern China .
NEW : 13 dead from a total of 60 cases of bird flu in China , authorities say . Comment: H7N9 was never known to infect people until last month . Cases of the virus have now spread to central and northern China .