Antimicrobial Resistance among Gram-Negative Bacilli Causing Infections in Intensive Care Unit Patients in the United States between 1993 and 2004

Abstract

During the 12-year period from 1993 to 2004, antimicrobial susceptibility profiles of 74,394 gram-negative bacillus isolates recovered from intensive care unit (ICU) patients in United States hospitals were determined by participating hospitals and collected in a central location. MICs for 12 different agents were determined using a standardized broth microdilution method. The 11 organisms most frequently isolated were Pseudomonas aeruginosa (22.2%), Escherichia coli (18.8%), Klebsiella pneumoniae (14.2%), Enterobacter cloacae (9.1%), Acinetobacter spp. (6.2%), Serratia marcescens (5.5%), Enterobacter aerogenes (4.4%), Stenotrophomonas maltophilia (4.3%), Proteus mirabilis (4.0%), Klebsiella oxytoca (2.7%), and Citrobacter freundii (2.0%). Specimen sources included the lower respiratory tract (52.1%), urine (17.3%), and blood (14.2%). Rates of resistance to many of the antibiotics tested remained stable during the 12-year study period. Carbapenems were the most active drugs tested against most of the bacterial species. E. coli and P. mirabilis remained susceptible to most of the drugs tested. Mean rates of resistance to 9 of the 12 drugs tested increased with Acinetobacter spp. Rates of resistance to ciprofloxacin increased over the study period for most species. Ceftazidime was the only agent to which a number of species (Acinetobacter spp., C. freundii, E. aerogenes, K. pneumoniae, P. aeruginosa, and S. marcescens) became more susceptible. The prevalence of multidrug resistance, defined as resistance to at least one extended-spectrum cephalosporin, one aminoglycoside, and ciprofloxacin, increased substantially among ICU isolates of Acinetobacter spp., P. aeruginosa, K. pneumoniae, and E. cloacae.Gram-negative bacilli (GNB) are a common cause of sepsis, pneumonia, urinary tract infections, and postsurgical infections in patients in acute care hospitals (14, 24). Antimicrobial resistance among GNB is increasing worldwide (21). This is a major public health problem and a cause for both substantial morbidity and mortality among hospitalized patients. A direct correlation has been shown between resistance of GNB and patient mortality, cost of patient care, and length of stay in the hospital (3,22,26,28). The problem of GNB resistance is of particular concern in the intensive care unit (ICU) setting.The most important determinant in the successful management of infections in patients in the ICU is prompt institution of effective empirical antimicrobial therapy; inappropriate empirical therapy affects both patient mortality rates and patient time spent in the ICU (12, 17). Optimizing empirical therapy requires knowledge of likely antimicrobial resistance patterns. With the aim of tracking resistance rates among GNB as the causes of infection in patients in U.S. ICUs, Merck Research Laboratories (Merck & Co., Upper Gwynedd, PA) established a multicenter laboratory-based surveillance program in 1993. Two previous reports from this investigation were published in 1996 and 2003 (13, 20). The current report describes the ...

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