The Significance of Bacterial Superinfection in Influenza

Abstract

During an epidemic of influenza A2 var. Hongkong and a subsequent period of high incidence of influenza B in Stockholm from January through April 1969, 130 influenza cases were selected for a study on the effects of bacterial superinfection. Bacterial involvement was demonstrated through frequent cultures from nose, throat, nasopharynx and sputum samples, together with serologic reactions in acute phase and convalescence sera against potentially pathogenic airway bacteria. It was found that bacterial involvement could not be shown statistically to influence the maximum temperature recorded, but did increase the duration of fever, the incidence of pneumonia, leukocytosis, and erythrocyte sedimentation rates over 50 mm/l h. When indicated by both bacterial findings and significant antibody titer increase, it also resulted in a higher frequency of granulocytosis. The bacteria most often involved were pneumococci, dominating in acute respiratory illness also in influenza-free periods, but the severity of staphylococcal superinfection in influenza was stressed by the involvement of Staph. aureus in 2 out of 6 fatal influenza cases.