Need for annual surveillance of antimicrobial resistance in Streptococcus pneumoniae in the United States: 2-year longitudinal analysis

Although changing patterns in antimicrobial resistance in Streptococcus pne umoniae have prompted several surveillance initiatives in recent years, the frequency with which these studies are needed has not been addressed. To a pproach this issue, the extent to which resistance patterns change over a I -year period was examined. In this study we analyzed S. pneumoniae antimicr obial susceptibility results produced in our laboratory with isolates obtai ned over 2 consecutive years (1997-1998 and 1998-1999) from the same 96 ins titutions distributed throughout the United States, Comparison of results r evealed increases in resistant percentages for all antimicrobial agents stu died except vancomycin. For four of the agents tested (penicillin, cefuroxi me, trimethoprim-sulfamethoxazole, and levofloxacin), the increases were st atistically significant (P < 0.05). Resistance to the fluoroquinolone remai ned low in both years (0.1 and 0.6%, respectively); in contrast, resistance to macrolides was consistently greater than 20%, and resistance to trimeth oprim-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 (repres entative 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 o f 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 a nnual basis, if not continuously.