Need for Annual Surveillance of Antimicrobial Resistance in Streptococcus pneumoniae in the United States: 2-Year Longitudinal Analysis

Abstract

Although changing patterns in antimicrobial resistance in Streptococcus pneumoniae have prompted several surveillance initiatives in recent years, the frequency with which these studies are needed has not been addressed. To approach this issue, the extent to which resistance patterns change over a 1-year period was examined. In this study we analyzed S. pneumoniae antimicrobial susceptibility results produced in our laboratory with isolates obtained over 2 consecutive years (1997-1998 and 1998-1999) from the same 96 institutions distributed throughout the United States. Comparison of results revealed increases in resistant percentages for all antimicrobial agents studied except vancomycin. For four of the agents tested (penicillin, cefuroxime, trimethoprim-sulfamethoxazole, and levofloxacin), the increases were statistically significant (P < 0.05). Resistance to the fluoroquinolone remained low in both years (0.1 and 0.6%, respectively); in contrast, resistance to macrolides was consistently greater than 20%, and resistance to trimethoprim-sulfamethoxazole increased from 13.3 to 27.3%. Multidrug resistance, concurrent resistance to three or more antimicrobials of different chemical classes, also increased significantly between years, from 5.9 to 11%. The most prevalent phenotype was resistance to penicillin, azithromycin (representative macrolide), and trimethoprim-sulfamethoxazole. Multidrug-resistant phenotypes that included fluoroquinolone resistance were uncommon; however, two phenotypes that included fluoroquinolone resistance not found in 1997-1998 were encountered in 1998-1999. This longitudinal surveillance study of resistance in S. pneumoniae revealed that significant changes do occur in just a single year and supports the need for surveillance at least on an annual basis, if not continuously.Resistance to ␤-lactams, macrolides, and trimethoprim-sulfamethoxazole (SXT) continues to increase among clinical isolates of Streptococcus pneumoniae. This trend, coupled with the potential for increasing resistance to fluoroquinolones, has prompted several surveillance studies in recent years (4-6, 10, 17, 22, 23). Although evolving patterns in antimicrobial resistance suggest clearly an exigency for such surveillance initiatives, the frequency with which studies are needed has not been addressed.The decision to expend resources to perform resistance surveillance must be based on a careful assessment of how frequently the data and information are needed. One approach to making this determination involves establishing the extent to which resistance rates and patterns change over a given time period. Among the surveillance reports published in recent years, there are substantial differences among institutions, geographic regions, and countries represented; the number of institutions involved; and the time periods during which the isolates were obtained (5,6,10,17,21,22). These differences make analysis of resistance change over time difficult, and only rarely have studies addressed the extent of changes in resista...

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