Antimicrobial use, with regard to both individual use and total antimicrobial consumption in the community, is strongly associated with nasopharyngeal carriage of penicillin resistant pneumococci in children. Control measures to reduce the prevalence of penicillin resistant pneumococci should include reducing the use of antimicrobials in community health care.

The relative effects of risk factors on the prevalence of resistant pneumococcal clones are hard to determine. Our aim was to evaluate the effect of risk factors on the prevalence of resistant pneumococci in Iceland in 2003 and compare these data with results of identical studies performed in 1993 and 1998. A randomized sample of 1,107 children was chosen from all 2,532 children 1 to 6 years old living in four communities. Pneumococci were carried by 64% of the 824 children enrolled and 9.5% were penicillin nonsusceptible (PNSP), as opposed to 8.1% (1998) and 8.5% (1993), and multiresistant strains of serotype 6B were 2.5% compared to 7.5% and 7.7% (p < 0.001). Antimicrobial use had declined in 10 years from 1.5 to 1.0 courses/child per year. The only significant risk factor for carriage of PNSP and erythromycin-resistant pneumococci was antimicrobial consumption. The multiresistant type 6B strains disappeared from the areas with the lowest antimicrobial use but maintained unchanged prevalence in the area with the highest use. The number of erythromycin- resistant, penicillin-susceptible strains of all pneumococci (37/475, 7.8%) increased significantly from the previous studies (7/353, 2.0%, 1998, and 2/390, 0.5%, 1993). This observation is associated with increased use of macrolides, especially azithromycin, in one of the study areas. Spread of novel resistant clones appears to be the main reason for rapid and significant changes in pneumococcal resistance rates. The choice of antimicrobial class appears to influence the selective environment favoring particular resistant clones.

The effects of community-wide interventions to reduce resistance rates are poorly understood. This study evaluated the effect of reduced antimicrobial usage on the spread of penicillin-nonsusceptible pneumococci (PNSP) in four communities in Iceland. The study was performed after interventions to reduce antimicrobial usage and compared to an identical study performed 5 years before. A randomized sample of 953 children was chosen from all 2,900 1- to 6-year-old children living in four well-defined communities. The main outcome measures were nasopharyngeal carriage of PNSP and individual and community use of antimicrobials. Pneumococci were carried by 51.7% of the 743 children enrolled, and 8.1% of the pneumococci were PNSP as opposed to 8.5% in the previous study. The antimicrobial use of participants had been reduced from 1.5 to 1.1 courses/year and the overall use among children <7 years old living in the study areas from 13.6 to 11.1 defined daily dosages/1000 children per day. The prevalence of PNSP increased in the two areas furthest away from the capital area despite reduced consumption. The major risk factors for carriage of PNSP remained the same. Interventions can be effective in reducing antimicrobial use. Pandemic multiresistant clones can also spread fast in small communities with low antimicrobial use, where their appearance may be delayed compared to highly populated urban areas. Clonal spread and herd immunity are important factors to be considered in the evaluation of intervention effects.

Parental expectations to antimicrobial treatment and awareness about resistance development appear to influence treatment strategies for AOM. The high rate of tympanostomy tube placement in preschool children does not result in reduced antimicrobial consumption.