Antibody response to P-protein in patients with Branhamella catarrhalis infections.

Branhamella catarrhalis is now recognized as an important cause of lower respiratory tract infections, especially in the elderly. In most instances, pathogenicity is presumed by recovery of the organism in a sputum culture, a method that is less than conclusive. In order to better diagnose B. catarrhalis infections, an enzyme-linked immunoassay has been developed using P-protein as antigen to measure antibodies to B. catarrhalis. In 17 elderly patients with B. catarrhalis pneumonia and 12 with tracheobronchitis, acute-phase serum antibody titers to P-protein were found to be significantly increased when compared with those of normal subjects (both p less than 0.02). There were no differences in antibody titers between patients with pneumonia and tracheobronchitis. Antibody titers of convalescent-phase sera increased over those of acute-phase sera in 46 percent of pneumonia patients and 50 percent of tracheobronchitis patients. The results demonstrated that lower respiratory tract infections with B. catarrhalis promote a significant elevation in antibody response to P-protein of B. catarrhalis.