Frequency of occurrence and antimicrobial susceptibility patterns for pathogens isolated from Latin American patients with a diagnosis of pneumonia: results from the SENTRY antimicrobial surveillance program (1998)

Abstract

The correct empiric choice of antimicrobial therapy in the treatment of pneumonia in hospitalized patients has established itself as a major therapeutic challenge to clinicians. Selection of an inappropriate antimicrobial agent could lead to increased rates of mortality and morbidity. Characteristics of pathogens responsible for this infection such as species prevalence, overall antimicrobial resistance rates, and mechanisms of detected resistance could serve as an invaluable resource to clinicians in making such therapeutic selections. This report addresses the aforementioned problems/needs by analysis of 712 strains isolated from the lower respiratory tract of patients hospitalized with a diagnosis of pneumonia in 10 Latin American medical centers in the SENTRY Antimicrobial Surveillance Program (1998). The four most frequently isolated pathogens (no/% of total) were: Pseudomonas aeruginosa (191/26.8%), Staphylococcus aureus (171/24.0%), Klebsiella spp. (86/12.1%), and Acinetobacter spp. (75/10.5%); representing nearly 75.0% of all isolates. More than 40 antimicrobial agents (23 reported) were tested against these isolates by reference broth microdilution methodology, and susceptibility profiles were established. The nonfermentative Gram-negative bacteria ( P. aeruginosa and Acinetobacter spp.) exhibited high levels of resistance to the agents tested. Amikacin (77.5% susceptible) was the most active drug tested against P. aeruginosa, followed by piperacillin/tazobactam (73.3% susceptible) > meropenem (72.8%) > imipenem (71.7%) as the only antimicrobials possessing a susceptibility rate of >70.0%. Only the carbapenem class compounds, imipenem (81.3% susceptible) and meropenem (78.3% susceptible) possessed susceptibility rates >50.0% against the Acinetobacter spp. isolates. Based on published interpretive criteria, over 22.0% of the Klebsiella spp. and 12.5% of the Escherichia coli were classified as extended spectrum β-lactamase (ESBL) producers. Of the cephalosporin class compounds tested against the Klebsiella spp. and E. coli isolates, cefepime demonstrated the highest rates of susceptibility (84.9% and 91.7%, respectively). This compound also fared well against the Enterobacter spp. isolates, inhibiting 88.2% of the isolates tested, many of which were resistant to ceftazidime and ceftriaxone. Resistance to oxacillin among the S. aureus isolates was nearly 50.0%, with vancomycin, teicoplanin, and the streptogramin combination quinupristin/dalfopristin inhibiting all isolates. Several clusters of multiply resistant organisms were also observed, and further characterization by ribotyping and pulsed-field gel electrophoresis established possible patient-to-patient spread. The results of this study indicate that rates of resistance among respiratory tract pathogens continue to rise in Latin America, with specific concerns for the high prevalence of nonfermentative Gram-negative bacteria isolated, oxacillin resistance rates in S. aureus, and the epidemic dissemination of multiply-resistant strains in several medical centers. International surveillance programs (SENTRY) should assist in the control of escalating antimicrobial resistance in this geographic area.