Persistence of resistance: a panel data analysis of the effect of antibiotic usage on the prevalence of resistance.

The use of antibiotics promotes the emergence of resistant bacteria in the patient and the environment. The extent of this well-documented biological relationship is, however, not well characterized at an ecological level. To make good policy around antibiotic use, it is important to understand the empirical connection between usage and resistance. We provide a consistent approach to estimate this relationship using national-level surveillance data. This paper estimates the effect of antibiotic usage on antibiotic resistance using an 11-year panel of data on both usage and resistance for 26 antibiotic-bacteria combinations in 26 European countries. Using distributed-lag models and event-study specifications, we provide estimates of the rate at which increases in antibiotic usage at the national level affect antibiotic resistance nationally and internationally. We also calculate the persistence of resistance and analyze how resistance behaves asymmetrically with respect to increases and decreases in usage. Our analysis finds the prevalence of resistant bacteria increases immediately after usage and continues to increase for at least 4 years after usage. We show that a decrease in usage has little identifiable impact on resistance over the same period. Usage in neighboring countries increases resistance in a country, independent of usage in that country. Trends in usage-related resistance vary across European regions and across bacterial classifications.