Resistance to many commonly used antibiotics has been steadily increasing for years. The Tracking Resistance in the United States Today (TRUST) surveillance program has been tracking this problem annually since 1998. Karlowsky and colleagues present the results of the 2001–2002 TRUST survey, and delineate clinical factors associated with pneumococcal antibiotic resistance.

This survey obtained 7,671 isolates of Streptococcus pneumoniae from 239 participating hospital laboratories throughout the United States. Antibiotic resistance was defined according to the minimum inhibitory concentrations (MICs) set for the medications by the National Committee for Clinical Laboratory Standards.

Comparing the 1998–99 respiratory infection season with the 2001–02 season, pneumococcal isolates resistant to penicillin increased from 14.7 to 18.4 percent. The greatest overall increase in MIC for an antibiotic occurred with azithromycin, which increased in the overall prevalence of resistance from 22.7 to 27.5 percent. Pneumococcal susceptibility to trimethoprim-sulfamethoxazole (TMP-SMX) improved slightly, with a drop in the resistance rate from 27.3 to 26.0 percent. Low resistance rates were still reported for ceftriaxone (range: 1.6 to 2.5 percent over the four years of data) and levofloxacin (slowly rising from 0.5 to 0.9 percent).

Resistance rates in isolates from patients younger than 18 years were consistently higher for all antibiotics except levofloxacin, which is typically not used in children. Isolates obtained from lower respiratory tract sites were more likely to demonstrate resistance than blood culture samples. Co-resistance to other antibiotics was associated strongly with penicillin resistance, especially for azithromycin (76.3 percent of penicillin-resistant isolates also were resistant to this macrolide) and TMP-SMX (87.3 percent co-resistance). Ceftriaxone co-resistance was 9.1 percent, and a few isolates were resistant to both penicillin and levofloxacin (1.3 percent).

Antibiotic resistance varied somewhat by region. Isolates from the West South Central census region (Texas, Oklahoma, Arkansas, Louisiana) were the most likely to demonstrate resistance, while those from the New England area had the lowest rates of resistance. The variation in resistance rates across regions was widest for TMP-SMX (differences as great as 21.9 percent among areas during the four years of surveillance). The least variation was noted with levofloxacin (only 0.5 to 1.9 percent differences during the four years of surveillance).

The authors conclude that pneumococcal antibiotic resistance rates across the nation have steadily climbed, from 1998 to 2002, for penicillin and azithromycin. Most isolates remain sensitive to ceftriaxone and levofloxacin. Younger patients and those with penicillin-resistant isolates are more likely to have pneumococcal infections caused by multi–drug-resistant organisms.