Measuring and interpreting associations between antibiotic use and penicillin resistance in Streptococcus pneumoniae

Studies of the relationship between antibiotic use and resistance in pneumo cocci have produced conflicting results, reflecting differences in study de sign, setting, and measures of association used. Mathematical models of pne umococcal transmission dynamics provide a framework for interpreting and re conciling these studies. The model predicts, and the review of published st udies confirms, that treatment often has little effect in increasing an ind ividual's absolute risk of carrying/being infected by penicillin-resistant Streptococcus pneumoniae (PRSP). However, treatment substantially increases a patient's risk of carriage of/infection by PRSP relative to that of peni cillin-susceptible S. pneumoniae (PSSP). The appropriate measure of associa tion depends on the question of interest. Antibiotic use can substantially increase the prevalence of risk in the community as a whole, even when ther e is a small or nonexistent effect of treatment on the absolute risk that a treated individual will carry a resistant organism. Recommendations for th e design and analysis of future studies of antibiotic treatment and pneumoc occal resistance are proposed.