Moraxella catarrhalis--an uncommon cause of community-acquired pneumonia in Swedish children.

In 284 Swedish children with community-acquired, roentgenologically verified pneumonia, antibodies to Moraxella (Branhamella) catarrhalis were determined in paired serum samples with an enzyme immunoassay using a whole-cell antigen preparation from 10 strains of M. catarrhalis. Only 9 children (3%) had significant increases in antibodies to M. catarrhalis. Among these 9 children, 11-39 months of age, 6 had serologic evidence of concurrent infection with other respiratory pathogens such as S. pneumoniae, non-capsulated H. influenza, RS virus and adenovirus. In 6 (67%) of the 9 children with antibody response and in 74 (27%) of the 275 children without antibody response to M. catarrhalis, nasopharyngeal cultures yielded growth of this bacterium. M. catarrhalis seems to be a common commensal in the upper respiratory tract, but a rare cause of pneumonia in children.