TRUST 2002 Study Shows Levofloxacin Resistance Remains Rare in S. pneumoniae

Resistance to commonly prescribed antibiotics is increasing among Streptococcus pneumoniae, a leading cause of respiratory illness. In the early 1990s, resistance to penicillin became a concern, however, in the last five years (1998-2002), S. pneumoniae has also exhibited increased resistance to other antibiotic classes, such as the macrolides (e.g. azithromycin, clarithromycin) and sulfonamides (e.g. trimethoprim-sulfamethoxazole). In the current U.S. study, the extent of resistance among S. pneumoniae was analyzed on both national and regional levels for the 2001-2002 respiratory season. The findings are presented at the 42nd Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC) in San Diego, on Sept. 29, 2002.

The findings are the result of the surveillance study, TRUST (Tracking Resistance in the U.S. Today) that was conducted by the Focus Technologies laboratory during the past respiratory season (TRUST 6, 2001-2002) to monitor changes in antibiotic resistance among S. pneumoniae. TRUST studies were initiated in 1996 to coincide with the release of levofloxacin into clinical use in the United States. The current study was the sixth consecutive study of respiratory pathogens conducted since the 1996-1997 respiratory season, and the current study consisted of 7,671 pneumococcal isolates collected from 238 clinical hospital laboratories geographically dispersed throughout 49 states. TRUST is the largest and most comprehensive annual surveillance program to monitor antimicrobial resistance among clinical isolates of S. pneumoniae in the United States.

Resistance to penicillin (18.4%) exceeded that reported in the previous 2000-2001 respiratory season (16.9%). Penicillin resistance data analyzed among the nine U.S. Bureau of the Census regions showed the highest prevalence in the West South Central (29.5%), East South Central (25.0%), and South Atlantic (23.3%) regions.

In the 2001-2002 TRUST study, resistance remained high for azithromycin (27.5%) and trimethoprim-sulfamethoxazole (26.0%), and remained very low for levofloxacin (0.9%). Analysis showed that azithromycin and trimethoprim-sulfamethoxazole minimal inhibitory concentrations (MICs) closely correlated with penicillin MICs , while levofloxacin MICs did not.

As observed in the previous three respiratory seasons, resistance to penicillin, azithromycin, and trimethoprim-sulfamethoxazole was commonly present in the same isolates of S. pneumoniae. Levofloxacin resistance remained rare (<1%) among the isolates collected during 2001-2002. The levofloxacin MIC90 value of 1 mg/ml and the MIC distributions for levofloxacin have not changed over the past four respiratory seasons.

TRUST studies are performed seasonally at Focus Technologies, Inc. (Herndon, Va.) They are conducted to measure rates of resistance to several anti-infective agents commonly prescribed in the U.S. and are based on in vitro laboratory data. While they provide an analysis of antibiotic resistance in the laboratory, they cannot assess clinical patient outcomes. Large surveillance studies such as TRUST enable the medical community (clinicians, laboratorians, pharmacists, etc.) to stay informed about increasing antibiotic resistance in a timely fashion.

Financial support to conduct TRUST studies and this presentation was provided by Ortho-McNeil Pharmaceutical, Inc., Raritan, N.J.