This article originally appeared on VICE News.
This year China endured the biggest outbreak of bird flu ever recorded, the US Centers for Disease Control and Prevention reported Friday.
This flu strain — a virus technically named H7N9 — has flared up in China every year since March 2013, when it first broke out in the country. Yet this year's outbreak was more deadly than almost every previous outbreak combined: Between October 7, 2016, and August 7, 2017, 759 people were infected. Only about 1,550 cases of H7N9 have ever been reported, so this year alone accounts for half of all cases.
The flu carried a high mortality rate, killing 281 people in this period, nearly 40 percent of those infected.
People who contract the virus tend to develop severe pneumonia and need medical attention to recover, according to the World Health Organization. (The virus is typically spread through handling poultry, not person-to-person contact.)
Most of these cases were detected in mainland China, Hong Kong, or Macao, while a few included people who'd traveled from China. But the range of the flu also spread. In total, only 21 Chinese regions saw cases during the first four epidemics. This year, 30 regions reported H7N9 cases.
The H7 virus didn't become a major public health issue until 2013's outbreak; only one person is believed to have died from it between 1996 and 2012. The H7N9 strain is considered by the CDC to be "the influenza virus with the highest potential pandemic risk."