Pleuritic chest pain and blood-tinged sputum or frank hemoptysis occur in a few patients. As many as 40 percent of patients have had no underlying disease. Gram's stain of sputum shows few to many polymorphonuclear leukocytes but rare bacteria. The chest radiograph shows bilateral infiltrates that may be diffuse interstitial, perihilar-like pulmonary edema, or dense opacifications. Leukocytosis with left shift is variably present.
Mortality is high.
Secondary bacterial pneumonia should be suspected when fever, increasing cough, and sputum production develop after several days of improvement. Streptococcus pneumoniae is the most common bacterial pathogen, but Staphylococcus aureus is associated with 25 percent of cases and high mortality. S. aureus and certain other bacteria produce proteolytic enzymes that activate influenza hemagglutinin and enhance replication. Hemophilus influenzae and S. pyogenes are also recognized. Bacterial infections of the sinuses and ears are frequent.