It seems obvious that there should be a connection between antibiotic prescribing rates in human clinical care, and prevalence of resistance in the causative bacterial pathogens. Indeed this is the basis for antimicrobial stewardship programs, which are considered a key tool in the fight against escalating AMR. However the devil is in the detail, and deconvoluting the dynamics of the relationship between antimicrobial use and antimicrobial resistance is challenging. 

A new study from researchers at Harvard School of Public Health and Brigham and Women’s Hospital tackles the problem by looking at the seasonality of antibiotic prescribing and resistance, in the Boston setting. The study examined outpatient prescribing patterns across five drug classes, and looked at corresponding resistance prevalence in three common bacterial pathogens (Staphylococcus aureus, Escherichia coli, and Klebsiella pneumoniae).  

The two most heavily used drug classes – penicillins and macrolides – showed the greatest seasonality of use, both peaking in winter; the next most common drug class – quinolones – also showed seasonality but with two annual peaks, in both winter and summer; nitrofurans showed seasonality, peaking in summer; tetracycline prescribing was not seasonal. Interestingly, seasonal resistance was observed for all those drug classes showing seasonality of usage, but in all cases resistance peaked in winter, even for nitrofurans and quinolones where usage peaked in summer.  

As the authors note: “These findings challenge the simple model of antibiotic use independently selecting for resistance and suggest that stewardship strategies will not be equally effective across all species and antibiotics. Rather, seasonal selection for resistance across multiple antibiotic classes may be dominated by use of the most highly prescribed antibiotic classes, penicillins and macrolides.” 

Read the full study here in PLoS Biology.