Penicillin susceptibility of pneumococcal isolates causing acute otitis media in children: Seasonal variation

Background: During the past decade, the prevalence of nonsusceptible Streptococcus pneumoniae strains that cause acute otitis media (AOM) has increased to ∼30%, and the proportion of fully resistant strains has also increased. The purpose of this study was to determine whether seasonal variation in resistance exists among pneumococcal isolates from children with AOM. Methods: Between 1991 and 2003, children 2 months-8 years of age diagnosed with AOM according to stringent criteria underwent tympanocentesis in various clinical trials. Results: Cultures from 567 of 794 tympanocenteses (71.4%) performed between 1991 and 2003 yielded AOM pathogens. During 1991-1995, only 1 of 43 S. pneumoniae isolates recovered (2%) was nonsusceptible to penicillin. The present analysis focuses on the 691 cultures obtained during 1996-2003; of these, 491 (71.1%) yielded AOM pathogens, of which 165 (33.6%) were S. pneumoniae. Of the pneumococcal isolates, 52 (31.5%) were nonsusceptible to penicillin. The proportion of nonsusceptible strains of S. pneumoniae increased over time: 0 of 3 (0%) in 1996; 2 of 11 (18%) in 1997; 14 of 40 (35%) in 1998; 3 of 34 (9%) in 1999; 11 of 25 (44%) in 2000; 11 of 22 (50%) in 2001; 4 of 18 (22%) in 2002; and 7 of 12 (58%) in 2003 (Cochran Armitage trend test, P = 0.03). AOM caused by nonsusceptible S. pneumoniae was more likely to occur as the winter progressed (P = 0.03); a similar trend was noted for the proportion of nonsusceptible strains that were fully resistant. Conclusions: In children with AOM, an increase in the proportion of episodes caused by nonsusceptible S. pneumoniae as the winter months progress may serve as a potential factor in guiding antimicrobial therapy for such children.