Pneumonia associated with influenza virus infection

The history of influenza pandemics was reviewed and clinical manifestations of pneumonia associated with influenza virus infections are described and several typical cases are presented. Several types of pneumonia associated with the influenza virus infection have been reported: 1) influenza complicated by secondary bacterial pneumonia, 2) primary influenza virus pneumonia, 3) combined influenza virus and bacterial pneumonia. Secondary bacterial pneumonia often produces a syndrome that is clinically distinguishable from that of primary viral pneumonia. In primary influenza virus pneumonia, chest roentgenography revealed bilateral infiltrations but no consolidation. Histologically, diffuse alveolar damage and hemorrhagic bronchiolitis were frequently observed in primary influenza virus pneumonia, in which case the prognosis was the worst. Although rare, the possibility of cryptogenic organizing pneumonia associated with influenza virus infection should be recognized. H. influenzae, S. pneumoniae, or S. aureus were frequently associated with influenza viral infection, and treatment against these bacteria should be considered.