Resistance surveillance of Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis isolated in the United States, 1997-1998

A national antimicrobial resistance surveillance study was conducted from D ecember 1997 to May 1998 to determine the prevalence of antimicrobial resis tance in 6620 clinical isolates of Streptococcus pneumoniae, Haemophilus in fluenzae and Moraxella catarrhalis. In this centralized study, which involv ed 163 institutions located in 43 states, we determined MICs for representa tives of five antimicrobial classes: beta-lactams (penicillin, co-amoxiclav , cefuroxime, ceftriaxone), macrolides (azithromycin, clarithromycin), co-t rimoxazole, glycopeptides (vancomycin) and fluoroquinolones (levofloxacin). In most S. pneomoniae isolates, all antimicrobials were to be found active , but amongst penicillin-resistant isolates (MICs greater than or equal to 2 mg/L), resistance to other beta-lactams, macrolides and co-trimoxazole wa s common. For vancomycin and levofloxacin, however, activity was not associ ated with penicillin resistance. The prevalence of penicillin-nonsusceptibl e (intermediate and resistant) pneumococci was highest in the South Atlanti c (44%) and East South Central (43%) regions and lowest in the Mid-Atlantic (28%) and New England (28%) regions. Resistance to beta-lactams, macrolide s and co-trimoxazole was more commonly found amongst respiratory isolates t han blood isolates and in strains from patients less than or equal to 12 ye ars old than from older patients. beta-lactamase, which was detected in 33% of H. influenzae and 92% of M. catarrhalis strains, did not affect the act ivity of the beta-lactams under study other than ampicillin. Certain agents , such as vancomycin and the fluoroquinolones, remain highly active, and we ll-designed surveillance systems that monitor MIC distributions would be ne eded to detect a potential for reduced susceptibility. In addition, surveil lance programmes should be designed to collect information about associated resistance as well as differences in prevalence associated with region, sp ecimen source and patient age.