Researchers have discovered the first hard evidence suggesting that the bird flu that spread through China and alarmed the world earlier this year was transmitted from person to person.
Public health officials became greatly concerned that the avian flu could spread between people, rather than solely from birds to humans, since the deadly strain appeared to infect family members in clusters of cases. Since the virus appeared in February, 133 human cases of H7N9 were confirmed in China and one was confirmed in Taiwan. Forty-three people died, and the live poultry industry in China came to a complete halt.
In an epidemiological investigation published Tuesday in the British Medical Journal, geneticists analyzed samples of the virus taken from two infected people: a father and daughter. A look at the sequenced genomes revealed that the two viral samples were nearly identical. Since influenza tends to evolve and change rapidly as it is transmitted from host to host, scientists interpreted the samples' similarity to mean that it was highly probable that the father transmitted it directly to his daughter.
The father, 60, contracted the avian flu in March after being exposed to it in a live poultry market, and was later hospitalized. His daughter, 32, was not exposed to poultry, but did take care of him at his bedside with little protection. Both later died of multi-organ failure.
This is only probable case of person-to-person transmission. Public health workers tested 43 other people who came into contact with the infected father, and none were positive for avian influenza. Researchers stress that there's no evidence to support that the virus, in its current form, could be transmitted between people efficiently, or on a large scale.
"Does this imply that H7N9 has come one step closer towards adapting fully to humans?" James Rudge, of the London School of Hygiene and Tropical Medicine, and Richard Coker, of the National University of Singapore School of Public Health, wrote in an accompanying editorial. "Probably not. Crucially, there is still no evidence of sustained transmission among humans."
The rate of new infections have slowed dramatically since May. Only one new case was reported in June and July. As a result, panic over avian bird flu has subsided, but there is still cause for concern. The virus could return again next flu season, evolved in a way that is impossible to predict.
"The threat posed by H7N9 has by no mean passed," Rudge and Coker warn.
Source: Qi X, Qian Y, Bao C, et al. Probable person to person transmission of novel avian influenza A (H7N9) virus in Eastern China, 2013: epidemiological investigation. BMJ. 2013.
Rudge J, Coker R. Human To Human Transmission of H7N9. BMJ. 2013.