Study participants are a subset of those enrolled in the CR-MAC Protocol (CPCRA 048). Oropharyngeal swabs are taken at baseline and 4 months after randomization, and are used to isolate S. pneumoniae in culture. These isolates are tested for susceptibility to macrolides, penicillin, cephalosporins, quinolones, and TMP-SMX. The rates of pneumococcal colonization at baseline and 4 months after randomization are determined and used to estimate the impact of deferring MAC prophylaxis on carriage of antibiotic-resistant S. pneumoniae.