[Comparative features of pneumonia associated with influenza]

Three manifestations of pneumonia that are associated with influenza are well recognized: primary influenza viral pneumonia, secondary bacterial pneumonia and mixed viral and bacterial pneumonias. In an outbreak of influenza, primary influenza viral pneumonia has occurred predominantly. After a typical onset of influenza, there is a rapid progression of fever, cough and dyspnea. Physical examination and chest roentgenography reveal bilateral findings but no consolidation. A Gram stain of the sputum fails to reveal significant bacteria, and bacterial culture yield sparse growth of normal flora, where as viral cultures yield high titers of influenza virus. Such patients do not respond to antibiotics. Secondary bacterial pneumonia often produces a syndrome that is clinically distinguishable from that of primary viral pneumonia. Recrudescence of fever is associated with symptoms and signs of bacterial pneumonia such as cough, sputum production, and an area of consolidation detected on physical examination and chest roentgenography. Gram staining and the culture of sputum reveals a predominance of a bacterial pathogen, most often H. influenzae, S. pneumoniae, B. catarrhalis, or S. aureus. Such patients usually respond to specific antibiotic therapy. During an outbreak of influenza many cases an observed that do not clearly fit into either of the aforementioned categories. The disease is not relentlessly progressive, and yet the fever pattern may not be biphasic. These patients may have primary viral, secondary bacterial, or mixed viral and bacterial infection of the lung.