Compares the bactericidal effect of normal human serum on Moraxella catarrhalis (M. catarrhalis) isolated from the sputum of elderly patients with lower respiratory tract infection (LRTI) with M. catarrhalis isolated from the oropharynx of asymptomatic elderly people. Microbiology of M. catarrhalis; Likelihood of M. catarrhalis isolates in causing LRTI in the elderly.