(NaturalNews) China's National Disease Authority has confirmed that a man whose 24-year-old son died of the H5N1 strain of bird flu is also infected with the disease, raising concerns about human transmission of the virus.H5N1 is a particularly virulent and lethal strain of the influenza virus that primarily infects domestic and wild birds. So far, it does not spread easily between birds and humans, but health officials fear that it could mutate into a form that is highly contagious from human to human. Given the intensely lethal nature of the disease, such a strain could easily lead to a global health crisis.Neither the infected man, identified only by his surname Lu, nor his son were known to have had contact with infected poultry. Health officials are carrying out an analysis on the DNA of the viruses that infected the two men to determine if they are the same strain, or whether the men contracted the virus from different sources.A total of 69 people who had come into close contact with Lu's son have been quarantined, but health officials report that none of them have shown signs of the disease. This suggests that even if the infection did pass to Lu from his son, it is not yet a highly contagious form.Human-to-human transmission of avian flu has been confirmed in Hong Kong, Indonesia and Vietnam, but these have also not been highly contagious strains, spreading mostly within families whose members came into close contact.The National Disease Authority said that the World Health Organization, along with the authorities of Hong Kong, Macao, Taiwan and other governments had been notified of the case.A total of 27 human cases of bird flu have been confirmed in China, leading to 17 fatalities. In contrast, the 1918 flu pandemic, which killed between 50 and 100 million people worldwide, had a fatality rate of only 2 percent.