Perspective:

In 2007, the AHA published revised guidelines recommending the use of antibiotic prophylaxis only among patients at high (not moderate) risk. Since then, different studies examining the effects of the guideline revisions on the incidence of IE have had varying conclusions. This study from Canada, using administrative databases, tracked prescriptions for antibiotic prophylaxis among patients ≥65 years of age, and the incidence of hospitalization for new IE among patients 18-64 years and patients ≥65 years of age. A decrease in antibiotic prescriptions among moderate-risk patients ≥65 years suggests penetration into practice of the guideline recommendations in this group. Because the incidence of IE increased in both moderate-risk and high-risk groups following the change in guidelines, and because streptococcal species accounted for a decreasing proportion of IE cases over time, the authors concluded that the reduced use of antibiotic prophylaxis among moderate-risk patients was not responsible for the observed increased incidence in IE hospitalizations. Confounding factors include presumed differences in the nature of heart valve disease among patients of different ages, potential differences by age group in the penetration of guideline recommendations, a presumed underlying background shift in IE pathogens over time, and limitations using administrative databases for the diagnosis of IE and classification of infective pathogens. Although this study might add support to the argument that a reduced use of antibiotic prophylaxis is justified, the argument that the observed increase in IE incidence is unrelated to reduced antibiotic prophylaxis is speculative, and not necessarily reassuring.