In April, China took the drastic measure of shutting down 780 live poultry markets in order to stop the spread of H7N9 bird flu, a sometimes-lethal virus that had been quickly spreading. Reports of infection by the virus all but stopped following the shutdown, and researchers are now reporting that it was in fact the shutdown that caused the change. In a paper published tomorrow in The Lancet, researchers led from The University of Hong Kong report that shutting down live poultry markets brought about a "sudden and strong" 97 percent drop in the daily number of H7N9 infections in humans.

Though the correlation may seem obvious, the researchers note that prior studies hadn't explicitly confirmed that the shutdown was responsible for stopping the spread of H7N9. "Without this robust evidence, policymakers would struggle to justify further closures of [live poultry markets] because of the millennia-old culture of trading live birds and the potential huge economic loss on the poultry industry in China," Benjamin J Cowling, the paper's lead author, says in a statement. The researchers report that some have pegged the economic loss of closing the markets between April and June at more than 57 billion Yuan, or around $8 billion.

The researchers' analysis is based off of infection reports from four major Chinese cities: Shanghai, Hangzhou, Huzhou, and Nanjing. Though the researchers admit that there may be environmental factors leading to the declining infection rates that they haven't considered, they note that humidity — the only factor that's been proven to interact with transmission of the flu — didn't come into play in this situation. Should H7N9 be detected once again in poultry, the researchers suggest that live markets be quickly shut down. The option may be expensive, but the response is both rapid and effective for preventing infections from the dangerous virus.