Antimicrobial resistance in respiratory tract pathogens: results of an international surveillance study

An international surveillance study was performed to assess the resistance patterns among respiratory tract pathogens during the winter of 1997-1998. The pathogens studied included Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis. The antibiotics tested included five beta-lactams (penicillin, ampicillin, amoxicillin, amoxicillin-clavulanic acid, cefuroxime axetil and ceftriaxone), two macrolides (azithromycin and clarithromycin), one sulfonamide (trimethoprim-sulfamethoxazole), one glycopeptide (vancomycin) and one fluoroquinolone (levofloxacin). A total of 11,502 isolates were tested from nine countries, using microdilution susceptibility tests as recommended by National Committee for Clinical Laboratory Standards (NCCLS) guidelines. The susceptibility rates varied greatly around the world. Ninety percent of M. catarrhalis isolates produced beta-lactamase, making them resistant to ampicillin. beta-Lactamase production by H. influenzae ranged from 5% in Germany to 34% in the USA (mean 17.5%). Of the S. pneumoniae isolates, 32.8% had some resistance to penicillin, but this ranged greatly from 7.8% in Germany to 66.5% in France. Penicillin resistance in S. pneumoniae was associated with resistance to other beta-lactams, macrolides and sulfonamides, but not to levofloxacin or vancomycin. All isolates of H. influenzae and M. catarrhalis were susceptible to levofloxacin. Results of this study support the conclusion that these three respiratory tract pathogens are becoming more resistant to selected antimicrobials, and that the level of resistance in these isolates to the antimicrobials varies greatly from one country to another.