The epidemiology of antibiotic resistance in hospitals: Paradoxes and prescriptions

A simple mathematical model of bacterial transmission within a hospital was used to study the effects of measures to control nosocomial transmission o f bacteria and reduce antimicrobial resistance in nosocomial pathogens. The model predicts that: (i) Use of an antibiotic for which resistance is not yet present in a hospital will be positively associated at the individual l evel (odds ratio) with carriage of bacteria resistant to other antibiotics, but negatively associated at the population level (prevalence). Thus infer ences from individual risk factors can yield misleading conclusions about t he effect of antibiotic use on resistance to another antibiotic. (ii) Nonsp ecific interventions that reduce transmission of all bacteria within a hosp ital will disproportionately reduce the prevalence of colonization with res istant bacteria. (iii) Changes in the prevalence of resistance after a succ essful intervention will occur on a time scale of weeks to months, consider ably faster than in community-acquired infections. Moreover, resistance can decline rapidly in a hospital even if it does not carry a fitness cost. Th e predictions of the model are compared with those of other models and publ ished data. The implications for resistance control and study design are di scussed, along with the limitations and assumptions of the model.