From November 1997 to April 1998, 1,601 clinical isolates of
Streptococcus
pneumoniae
were obtained from 34 U.S. medical centers. The overall rate of strains
showing resistance to penicillin was 29.5%, with 17.4% having intermediate resistance.
Multidrug resistance, defined as lack of susceptibility to penicillin and at least two other
non-ß-lactam classes of antimicrobial drugs, was observed in 16.0% of isolates.
Resistance to all 10 ß-lactam drugs examined in this study was directly related to the
level of penicillin resistance. Penicillin resistance rates were highest in isolates from
middle ear fluid and sinus aspirates of children <5 years of age and from patients in
ambulatory-care settings. Twenty-four of the 34 medical centers in this study had
participated in a similar study 3 years before. In 19 of these 24 centers, penicillin
resistance rates increased 2.9% to 39.2%. Similar increases were observed with rates
of resistance to other antimicrobial drugs.