Influenza A (H1N1) is an acute respiratory infectious disease caused by mutant influenza A virus subtype H1N1. The pathogen is a new virus emerging after virus gene recombination of swine influenza, avian influenza, and human influenza. Influenza A (H1N1) is transmitted commonly via respiratory droplets and direct or indirect contact. Clinically, influenza A (H1N1) is characterized by influenza-like symptoms such as fever, cough, and rhinorrhea. But in rare serious cases, the condition may progress rapidly, with occurrence of viral pneumonia, respiratory failure, and multiple organ failure. Even death occurs in serious cases, with a mortality rate of 23–25 %. On April 30, 2009, influenza A (H1N1) was officially listed into Class B infectious diseases in China. Since then, it has been managed according to the Infectious Disease Prevention and Control Act in China. Meanwhile, it has been introduced into the category of quarantinable infectious disease for management based on the Frontier Health and Quarantine Law of China.
Influenza A (H1N1)