The influence of bacterial superinfection on the clinical course of influenza. Studies from the influenza epidemics in Stockholm during the winters 1969-70 and 1971-72.

During two epidemics of influenza A infection in Stockholm 1969-72, 249 cases were selected for a study on the effect of bacterial superinfection. Bacterial involvement was demonstrated through cultures and serologic reactions. The occurrence of C-reactive protein in increased amount in serum was significantly more common in the group which had the strongest indication of bacterial infection. An increased duration of fever, and a higher incidence of pneumonia, leukocytosis and erythrocyte sedimentation rate over 50 mm/l h was also the rule in cases with bacterial involvement. During both epidemics the bacteria most often involved were pneumococci.