We compared rates of antibiotic resistance in strains of Streptococcus pneumoniae recovered from nasopharyngeal secretions of a group of children studied longitudinally in a research day care center between 1978 and 1985 and recovered from usually sterile body fluids of patients at a tertiary care hospital between 1981 and 1985. The prevalence of trimethoprim-sulfamethoxazole (TMP-SMZ) resistance was 11.5% in isolates from the hospital, whereas 30.0% of episodes of nasopharyngeal carriage of S. pneumoniae studied in day care children included TMP-SMZ-resistant isolates. The proportion of episodes of colonization with TMP-SMZ-resistant isolates in the day care study increased from 5.4% before 1981 to 39% between 1981 and 1985. Isolates of S. pneumoniae relatively resistant (MIC greater than or equal to 0.125 micrograms/mL) to penicillin G, amoxicillin, or cefuroxime accounted for 8% of isolates from the hospital and 11.9% of episodes of nasopharyngeal colonization in children in day care. Pneumococci with reduced susceptibility to either TMP-SMZ or a beta-lactam antibiotic were recovered from 68% of 72 children in the day care study.

During a 1-year period, the prevalence of thymidine-dependent (TD) Staphylococcus aureus in patients at two geographically distinct cystic fibrosis (CF) centers was determined. Of 200 CF patients who had their respiratory secretions cultured, 95 harbored S. aureus, and 20 (21%) had TD S. aureus as their predominant staphylococcal isolate. All 20 TD S. aureus-positive patients had received trimethoprim-sulfamethoxazole for an average of 30.9 months. It was also observed that TD S. aureus exhibited aberrant colony morphologies or did not grow on media commonly used in CF centers for S. aureus isolation, suggesting that this organism could be missed by routine culture methods. In contrast, all 20 isolates had typical staphylococcal morphology on mannitol salt agar after 48 h of incubation. Mannitol salt agar is recommended for primary isolation of TD S. aureus.