Two more cases of a new and deadly influenza virus have been diagnosed in Hong Kong. On Saturday, public health authorities announced that a 54-year-old man and a 13-year-old girl had both contracted an influenza strain that before this spring was thought to infect only birds. "This was not good news to hear. We're very concerned," says Dominick Iacuzio, an influenza specialist at the National Institute of Allergy and Infectious Diseases in Bethesda, Maryland.
Because strains of flu that infect birds usually cannot infect people (Science, 12 September, p. 1600), humans have not built up any immunity to such avian viruses. As a result, almost everyone would be susceptible if the virus could spread. The latest infections are the third and fourth instance of an apparent bird-to-human jump in the last 8 months. The World Health Organization reported today that the man died of lung complications. The girl is still hospitalized in intensive care, but her condition is improving.
A team of scientists from the U.S. Centers for Disease Control and Prevention (CDC) in Atlanta is in Hong Kong, working with authorities there to determine how the latest victims caught the virus. Neither of the new victims is known to have had contact with the two previously reported victims. "The main question is to determine if there is person to person transmission or if [the victims] had been in contact with sick birds," says CDC epidemiologist Nancy Arden. "It's very hard to know at this point what [the new cases] mean." However, she says, if the virus were easily transmissible, "we would expect to see far more cases than we've seen so far."