Antibiotic susceptibility of invasive Streptococcus pneumoniae in Wisconsin, 1999

Streptococcus pneumoniae is a major cause of community acquired infections in the United States, and rates of antibiotic resistance have increased dramatically in the past decade. Statewide rates of pneumococcal resistance to penicillin and other antibiotics have not been previously reported in Wisconsin. To determine these rates, we assessed invasive pneumococcal isolates for reduced susceptibility to nine different antibiotics.

Pneumococcal isolates from blood, cerebrospinal fluid or other normally sterile body sites were submitted by 91% of laboratories that perform invasive bacterial cultures. Isolates were tested for susceptibility to penicillin, cefotaxime, ceftriaxone, levofloxacin, meropenem, erythromycin, vancomycin, sulfamethoxazole-trimethoprim and chloramphenicol.

There were 409 invasive pneumococcal isolates identified in 1999 among Wisconsin residents, including 385 (94%) isolates from blood. The mean patient age was 42.5 years (range, < 1 year to 96 years), and 213 (52%) were male. Of the pneumococcal isolates, 24% were not susceptible to penicillin, including 10% with high level resistance. Isolates with reduced penicillin susceptibility were also likely to have reduced susceptibility to other antibiotics. Patients with penicillin nonsusceptible (intermediate and fully resistant) pneumococcal isolates were significantly younger (mean, 37.0 years) than those with susceptible isolates (mean, 44.3 years) (p = .04). The proportion of patients with a penicillin nonsusceptible isolate varied by region, ranging from 12.8% in northeastern Wisconsin to 35.5% in northern Wisconsin.

The proportion of invasive pneumococcal isolates with penicillin resistance in Wisconsin is similar to other regions of the United States. Inappropriate antibiotic use contributes to the emergence of resistant pneumococcal infections, and educational efforts are underway to promote judicious antibiotic use in Wisconsin.