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Haze and influenza A virus: Coincidence or causation?

      To the Editor:
      We previously reported the public health implications and consequences of an unprecedented dense haze that shrouded a significant portion of China.
      • Pan Q.
      • Yu Y.
      • Tang Z.
      • Xi M.
      • Zang G.
      Haze, a hotbed of respiratory-associated infectious diseases, and a new challenge for disease control and prevention in China.
      We reported that this atmospheric phenomenon was accompanied by an increase in respiratory diseases, and we described the new challenges for disease control and prevention that were facing the Chinese medical community because of the poor air quality. Unfortunately, 2 years later, the heavy haze has returned. According to the China Meteorological Administration, the most severe haze occurred during the months of November and December 2015.
      • China Meteorological Administration
      2015 China Climate Communique.
      Coincident with this period of dense haze, there was a substantial increase in the number of respiratory tract infections, particularly among pediatric patients. This unexpected outbreak led to many hospitals becoming overwhelmed. These overburdened hospitals were especially common in the densely populated municipality of Shanghai.
      Notably, in Shanghai, the proliferation of respiratory tract infections was accompanied by a surge in the number of influenza A virus (primarily H1N1) cases. We observed that the majority of patients who were presenting with influenza A virus infections were children. The magnitude of these influenza A virus infections reached the level of a small-scale epidemic among kindergartens, middle schools, and primary schools. Fortunately, no fatal cases were reported in Shanghai among those patients who received treatment with oseltamivir.
      The epidemiologic association between the occurrence of haze and the incidence of influenza A virus infection remains largely unknown.
      • Sooryanarain H.
      • Elankumaran S.
      Environmental role in influenza virus outbreaks.
      However, during the widespread and dense haze events that occurred during the winters of both 2013 and 2015, we observed a sharp increase in the number of patients with respiratory tract infection, especially influenza A virus infections. Therefore, it is important to understand whether a relationship exists between the occurrence of haze and the risk of influenza A virus infection. A number of important questions must be answered: Is the particulate dense air inhaled into the respiratory tract during a haze event a vector for pathogens, including influenza A virus?, Does heavy haze decrease the resistance of lung tissue to pathogenic microorganisms, thereby increasing the risk of respiratory disease?, and Does influenza A virus (with its naturally higher incidence during winter and spring) merely happen to coincide with the seasonal haze? Conflicting lines of evidence exist for each of these questions, and additional research and data will be needed to reach dependable conclusions.
      It is reassuring that, although still extreme in terms of scope, intensity, and duration, the haze of 2015 was weaker than the event that occurred during winter 2013. This improvement has been attributed to the Chinese government's substantial effort to control air pollution and improve the environment. Furthermore, there was a notable improvement in the ability of the Chinese CDC and medical institutions to cope with the influenza A virus epidemic that occurred in 2015 when compared with the response to the 2013 epidemic. However, the likely prospect of frequent and similar haze events indicates that the Chinese government and people should continue to prioritize air quality improvement.

      References

        • Pan Q.
        • Yu Y.
        • Tang Z.
        • Xi M.
        • Zang G.
        Haze, a hotbed of respiratory-associated infectious diseases, and a new challenge for disease control and prevention in China.
        Am J Infect Control. 2014; 42: 688
        • China Meteorological Administration
        2015 China Climate Communique.
        China Meteorological Administration, Beijing, China2015 (Available from:) (Accessed June 27, 2016)
        • Hu M.
        Hospitals struggle with flu cases.
        (Available from:) (Accessed December 21, 2015)
        • Cai W.
        H1N1 rises to top spot, but no fear of epidemic.
        (Available from:) (Accessed December 18, 2015)
        • Sooryanarain H.
        • Elankumaran S.
        Environmental role in influenza virus outbreaks.
        Annu Rev Anim Biosci. 2015; 3: 347-373