Trends in antimicrobial susceptibilities among Enterobacteriaceae isolated from hospitalized patients in the United States from 1998 to 2001

Longitudinal surveillance of Enterobacteriaceae for antimicrobial susceptibility is important because species of this family are among the most significant and prevalent human pathogens. To estimate rates of in vitro antimicrobial susceptibility among hospitalized patients in the United States, data from The Surveillance Network were studied for 14 agents tested against 10 species of Enterobacteriaceae (n=384,279) isolated from intensive-care-unit (ICU) patients and non-ICU inpatients from 1998 to 2001. Cumulative susceptibility (percent) data for all species of Enterobacteriaceae isolated from ICU patients and non-ICU inpatients, respectively, were ranked as follows: ampicillin-sulbactam (45.5 and 57.2) much less than ticarcillin-clavulanate (74.8 and 83.5) < trimethoprim-sulfamethoxazole (87.0 and 84.5) ≅ cefotaxime (82.9 and 92.6)=ceftazidime (82.3 and 91.0)=ceftriaxone (86.5 and 93.9)=piperacillin-tazobactam (83.5 and 90.5) < levofloxacin (89.3 and 90.6)=ciprofloxacin (91.0 and 91.7) < gentamicin (91.8 and 94.3) < cefepime (95.0 and 97.9) < amikacin (98.5 and 99.2) < imipenem (100 and 100)=meropenem (100 and 100). Of those agents studied only susceptibilities to ciprofloxacin (94 to 89%) and levofloxacin (93 to 89%) decreased in a stepwise manner from 1998 to 2001. Decreased fluoroquinolone susceptibility was most pronounced for Escherichia coli, Proteus mirabilis, and Enterobacter cloacae. For all species of Enterobacteriaceae, trimethoprim-sulfamethoxazole resistance was more commonly observed in isolates with a single-drug resistance phenotype while gentamicin and fluoroquinolone resistances were more common in isolates resistant to at least one additional class of antimicrobial agent. Ongoing surveillance of Enterobacteriaceae will be particularly important to monitor changes in fluoroquinolone susceptibility, as well as changes in the prevalence of isolates resistant to multiple classes of antimicrobial agents.