High rates of susceptibility to trimethoprim-sulfamethoxazole found.


SAN DIEGO—The empiric use of trimethoprim-sulfamethoxazole (SXT) to treat uncomplicated UTIs may be contributing to increased SXT resistance and multidrug resistance in the United States. 

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New study findings from a national database suggest that high levels of resistance to SXT (greater than 20% of isolates resistant) are widespread throughout the country among Escherichia coli UTI isolates. At the Infectious Diseases Society of America annual meeting here, researchers presented new data showing that high levels of resistance occur in six out of nine major regions of the United States. No clear correlation was found between SXT resistance and fluoroquinolone resistance rates among E. coli isolates.


The investigators found similar trends among other enteric gram-negative UTI isolates, but these isolates tended to be more susceptible to SXT than E. coli. Increased resistance to SXT among E. coli and its variability in different regions of the country emphasize the importance of local surveillance to guide management and treatment of uncomplicated UTIs, the researchers said.


“Physicians in their offices don’t usually have laboratory results to guide therapy for UTIs so they have to treat empirically, and empirically they have primarily used trimethoprim-sulfamethoxazole,” said study investigator Clyde Thornsberry, PhD, chief research advisor at Eurofins Medinet in Herndon, Va. “Some communities are now seeing resistance rates greater than 20%, indicating that they need to think about using another empiric agent because of the increased risk of failures with SXT. More often, these alternative agents are either levofloxacin, ciprofloxacin, or nitrofurantoin.”


Dr. Thornsberry and his colleagues analyzed antibiogram results from The Surveillance Network (TSN) for 2006. The network looks at regional and national trends in susceptibility to levofloxacin (LVX), SXT, ciprofloxacin (CIP) and ampicillin (AMP) among outpatient UTI isolates of E. coli and other enteric organisms.


Overall, the researchers found that E. coli isolates were more susceptible to LVX and CIP (87%) than SXT (79%) and AMP (58%). High levels of SXT resistance were observed in the West North Central (20%), Pacific (22%), Mountain (23%), East South Central (23%), South Atlantic (23%), and West South Central (25%) areas of the United States. High levels of resistance were not found in the New England, Middle Atlantic, and East North Central region. LVX susceptibility rates remained high in the West North Central and Mountain (89%), East South Central (87%), South Atlantic (83%), and West South Central (86%) areas.


Dr. Thornsberry said UTI isolates of enterics other than E.coli were most susceptible to LVX (89%), CIP (88%), and SXT (87%) and were least susceptible to AMP (29%). Overall, the study demonstrates that the susceptibility to LVX against enterics other than E. coli was 85% or greater in eight of the nine regions, and susceptibility to SXT was greater than 85% in seven regions.