Haze, a hotbed of respiratory-associated infectious diseases, and a new challenge for disease control and prevention in China.

To the Editor:

During 2013 an incessant dense haze shrouded nearly half of China, affecting approximately 800 million inhabitants. Previously, the southeast region, including Shanghai and the Pearl River Delta, had been enveloped in extreme haze; and before that, a similar situation occurred in northern China. Haze continues to wreak havoc throughout the country. Meanwhile, human infection with avian influenza A H7N9 virus reemerged during January 2014 and has led to 31 deaths. This number is almost as high as for all of 2013; more unfortunately, the attack rate of H7N9 infection was highly sporadic.

Environmental epidemiology research in recent decades has shown that hazy weather conditions are associated with increased morbidity due to respiratory infections and risks of other diseases. Last year after each bout of extremely hazy weather, the number of patients with respiratory diseases increased significantly; in these patients, some cases developed into severe pneumonia and death. The number of patient admissions for respiratory infection into the Infectious Diseases Department of our hospital in Shanghai increased by more than 3-fold over 3 months compared with the same period the previous year.

Small particulate matter of 2.5 microns in diameter or less (PM2.5), which is easily absorbed into the lungs, is considered to be the primary cause of the recent hazy weather in China. Researchers have explained that PM2.5 contains toxic chemicals and microparticles that attach to pathogenic microorganisms. When people are exposed to haze, PM2.5 can penetrate deeply into the lungs through the respiratory tract due to its small size, thus decreasing the resistance of lung tissue to pathogenic microorganisms and thereby increasing the risk of respiratory disease. Dr Hongzhou Lu (deputy director of the Shanghai Public Health Clinical Center for H7N9 bird flu) has declared that the recent hazy conditions increase the risk of respiratory infection, including H7N9, but do not directly result in the proliferation of viruses. Likewise, data from the Chinese Center for Disease Control and Prevention did not show severe acute respiratory syndrome or influenza virus outbreaks in the Chinese population during 2013, the worst year of haze in more than half a century in China. Despite the fact that haze-associated respiratory infection is not as serious as severe acute respiratory syndrome, a wide range, long duration, and high frequency of haze occurrence, coupled with its long-term effects, will bring new challenges to the Chinese medical community in the future.

The increasing number of cases of respiratory infection, especially skyrocketing cases of human infection with avian influenza A H7N9 virus during January 2014, forced the Chinese Center for Disease Control and Prevention as well as medical institutions to prepare to actively meet the challenge. The National Health and Family Planning Committee has plans to collect first-hand data through the establishment of the National Haze Health Effects Monitoring Network to find strategies and administrate policy in the future. The Environmental Protection Department is also actively setting more stringent industry standards to control the sources of haze.

Although masks can reduce inhalation of harmful substances and the incidence of haze-related respiratory diseases, haze governance and improving air quality are effective means to reduce the attack rate of haze-related respiratory diseases. After all, economic development should not be at the expense of people's health.