Bird flu more difficult to detect this time around

China has suffered outbreaks of bird flu before, but the virus that has now infected more than 100 people across eastern China and Taiwan is different in several important ways, according to scientists and researchers.

The new virus is H7N9, a different strain than the H5N1 flu that caused previous outbreaks. Other strains of the flu showed telltale signs in infected birds, but this time, infected birds show no apparent signs of the illness, confounding efforts to detect and stop the flu where it starts.

H7N9 also appears to be more easily spread from poultry to humans than H5N1, a World Health Organization expert told reporters this week, calling the new virus “one of the most lethal influenza viruses that we have seen so far.” There is no evidence yet of it spreading from person to person, but the WHO has warned that the virus could gain that ability in the future, increasing the threat.

The new strain may affect people in a wider range of ages than H5N1, according to a new report released Wednesday by doctors and researchers from several public health agencies. Patients are disproportionately older men; H5N1 patients had a median age of 26.

Poultry markets in some affected regions have been shut down, but so far health officials have not recommended slaughtering large numbers of poultry to stop the flu, which was one of the tools used to stop H5N1, the Associated Press reported Thursday. Public health researchers have said that health officials should consider culling the birds until scientists can figure out how the virus spreads.

That could be harder this time, though, because “you’re trying to convince people providing poultry to cull birds that appear to be perfectly healthy,” said Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota.

So far, the death rate among people infected with the new virus appears to be lower than for the older strain of bird flu, according to the report released Wednesday. Researchers seem to have been aggressive in identifying patients infected with H7N9, even if they have not been hospitalized.

However, Osterholm pointed out that scientists are often even more concerned about less deadly viruses because they may have a greater chance to spread and ultimately kill more people.

This round of the bird flu has caused added panic in China because pigs, ducks and sparrows are dying en masse, The Times’ Barbara Demick wrote last week. Health authorities have not found any links between the animal deaths and the bird flu, but “the panic is linked to the confusion about what is going on,” Rabobank food industry analyst Jean-Yves Chow told The Times.

The new flu also has been seen as a test of transparency for China, which suppressed information about the spread of SARS and other deadly viruses in the past. This time, state media have reported regularly on the flu, noting new cases and updates. A WHO official on Wednesday called the Chinese response “exemplary,” crediting government agencies with acting quickly.

Others were cautious about celebrating the Chinese response. “This is progress.... Chinese officialdom may have been chastened, to some extent, by the disastrous consequences” of covering up severe acute respiratory syndrome, Asia Society fellow Susan Jakes wrote for its ChinaFile magazine. “And there’s no question that technology has made guarding ‘sensitive’ information more difficult.

“But that doesn’t mean Beijing has embraced transparency in the ensuing years,” she added.

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