Effect of antimicrobial use and other risk factors on antimicrobial resistance in pneumococci.

Penicillin-resistant and multi-resistant pneumococci have spread globally and reached high prevalence in many countries. Antimicrobial use is considered a major driving force for resistance, although the influence in the community has not been as clearly demonstrated. Other risk factors may be important, and only with a clear understanding of the risk factors can effective control measures be introduced. The main habitat of the pneumococcus is the nasopharynx of children. Carriage increases from birth and is maximal at pre-school age. Antimicrobial use in children is likely to have a significant influence on the susceptibility of pneumococci. Most studies looking for risk factors for resistance in pneumococci have identified antimicrobial use as a risk factor, especially the following aspects: ongoing, recent, repeated, frequent, and prophylactic antibiotic use. The effect of individual classes of antimicrobials has not been studied in detail but use of beta-lactam antibiotics and trimethoprim-sulpha has been associated with increased risk. Other risk factors are young age, nosocomial acquisition, prior hospitalization, and HIV infection. Day-care centers can facilitate the spread of resistant pneumococci and an Icelandic study showed that carriage of resistant pneumococci was associated with young age, domicile in an area with high antimicrobial consumption, recent antimicrobial use, frequent antimicrobial use, and use of trimethoprim-sulpha. The rapid increase of penicillin-resistant pneumococci in Iceland was met with propaganda against overuse of antimicrobials, which lead to reduction of antimicrobial use and subsequently a reduced incidence of penicillin-resistant pneumococci. This reduction may be related to reduced antimicrobial use. Reducing antimicrobial use should be considered important for programs aimed at reducing antimicrobial resistance.