Studies of antibiotic resistance within the patient, hospitals and the community using simple mathematical models

The emergence of antibiotic resistance in a wide variety of important patho gens of humans presents a worldwide threat to public health. This paper des cribes recent work on the use of mathematical models of the emergence and s pread of resistance bacteria, on scales ranging from within the patient, in hospitals and within communities of people. Model development starts withi n the treated patient, and pharmacokinetic and pharmacodynamic principles a re melded within a framework that mirrors the interaction between bacterial population growth, drug treatment and the immunological responses targeted at the pathogen. The model helps identify areas in which more precise info rmation is needed, particularly in the context of how drugs influence patho gen birth and death rates (pharmacodynamics). The next area addressed is th e spread of multiply drug-resistant bacteria in hospital settings. Models o f the transmission dynamics of the pathogen provide a framework for assessi ng the relative merits of different forms of intervention, and provide crit eria for control or eradication. The model is applied to the spread of vanc omycin-resistant enterococci in an intensive care setting. This model frame work is generalized to consider the spread of resistant organisms between h ospitals. The model framework allows for heterogeneity in hospital size and highlights the importance of large hospitals in the maintenance of resista nt organisms within a defined country. The spread of methicillin resistant Staphylococcus aureus (MRSA) in England and Wales provides a template for m odel construction and analysis. The final section addresses the emergence a nd spread of resistant organisms in communities of people and the dependenc e on the intensity of selection as measured by the volume or rate of drug u se. Model output is fitted to data for Finland and Iceland and conclusions drawn concerning the key factors determining the rate of spread and decay o nce drug pressure is relaxed.