As the human death toll from the H7N9 bird flu in China rose to 17 with a total of 82 confirmed cases, various health authorities announced that the new strain of avian influenza may be more contagious than previously thought.
Global and Chinese agencies alike said a significant portion of people who have tested positive for the H7N9 bird flu disease have not been in contact with poultry.
Dr. Zeng Guang, the chief of epidemiology at China’s Center for Disease Control and Prevention, estimates that roughly 40 percent of those who have tested positive for H7N9 have not had recent contact with poultry.
“How were they infected? It is still a mystery,” Zeng told Beijing News.
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World Health Organization spokesman Gregory Hartl confirmed that some patients with the disease “have no history of contact with poultry.” This suggests that human-to-human infection is a possibility.
Previous reports by the CDC were that those who came in contact with H7N9-infected people had shown no symptoms.
“H7N9 is completely different from SARS [a disease spread through human contact], and those who had contact with the nine patients have no relevant symptoms,” Feng Zijian, director of the emergency center at the CDC said in early April. “No human-to-human transmission of H7N9 has been discovered and no epidemiological connection between these cases has been found so far.”
Now, human-to-human transmission cannot be ruled out.
“This is one of the puzzles still [to] be solved and therefore argues for a wide investigation net,” Hartl said. “It might be because of dust at the wet markets, it could be another animal source beside poultry, it could also be human-to-human transmission,” he said.
Feng also pointed out that during the last bird flu outbreak in 2008, reports about how it was spread may have been inaccurate because patients could not remember if they were in contact with poultry. Feng also told reporters that he maintains that those infected with H7N9 must have come in contact with birds directly, or unknowingly have been in contact with a contaminated environment.
For the most part, Chinese have remained calm because of the seemingly honest and rapid reporting by health officials, a considerable change from the SARS epidemic, which spread through the nation in 2003 amid silence from authorities.
Though Shanghai officials effectively slaughtered all poultry in agricultural markets where the H7N9 disease was found, if evidence of human transmission is confirmed, it will likely become more difficult to contain the disease.
The diagram above, which can be viewed larger here, was created by Information Is Beautiful, and depicts the various influenza strains that humans and various animals are susceptible to.