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Caring for the Critically Ill Patient |

Antibiotic Resistance Among Gram-Negative Bacilli in US Intensive Care Units:  Implications for Fluoroquinolone Use FREE

Melinda M. Neuhauser, PharmD; Robert A. Weinstein, MD; Robert Rydman, PhD; Larry H. Danziger, PharmD; George Karam, MD; John P. Quinn, MD
[+] Author Affiliations

Author Affiliations: Department of Clinical Sciences and Administration, University of Houston College of Pharmacy, Houston, Tex (Dr Neuhauser); Department of Medicine, Rush Medical College, Chicago, Ill (Drs Weinstein and Quinn); Department of Medicine (Drs Weinstein and Quinn) and Department of Emergency Medicine (Dr Rydman), Cook County Hospital, Chicago, Ill; School of Public Health (Dr Rydman) and Department of Pharmacy Practice (Dr Danziger), University of Illinois at Chicago; and Department of Medicine, Louisiana State University School of Medicine, New Orleans (Dr Karam).


Caring for the Critically Ill Patient Section Editor:Deborah J. Cook, MD, Consulting Editor, JAMA.


JAMA. 2003;289(7):885-888. doi:10.1001/jama.289.7.885.
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Published online

Context Previous surveillance studies have documented increasing rates of antimicrobial resistance in US intensive care units (ICUs) in the early 1990s.

Objectives To assess national rates of antimicrobial resistance among gram-negative aerobic isolates recovered from ICU patients and to compare these rates to antimicrobial use.

Design and Setting Participating institutions, representing a total of 43 US states plus the District of Columbia, provided antibiotic susceptibility results for 35 790 nonduplicate gram-negative aerobic isolates recovered from ICU patients between 1994 and 2000.

Main Outcome Measures Each institution tested approximately 100 consecutive gram-negative aerobic isolates recovered from ICU patients. Organisms were identified to the species level. Susceptibility tests were performed, and national fluoroquinolone consumption data were obtained.

Results The activity of most antimicrobial agents against gram-negative aerobic isolates showed an absolute decrease of 6% or less over the study period. The overall susceptibility to ciprofloxacin decreased steadily from 86% in 1994 to 76% in 2000 and was significantly associated with increased national use of fluoroquinolones.

Conclusions This study documents the increasing incidence of ciprofloxacin resistance among gram-negative bacilli that has occurred coincident with increased use of fluoroquinolones. More judicious use of fluoroquinolones will be necessary to limit this downward trend.

Figures in this Article

Susceptibility data derived from national surveillance can be a barometer for emerging resistance problems.1,2 Previously, we published the results of a national intensive care unit (ICU) surveillance study of aerobic gram-negative bacilli collected between 1990-1993.3 The study revealed a rising incidence of ceftazidime-resistant Klebsiella pneumoniae and Enterobacter species in ICUs. The purpose of the current study was to describe national rates of antimicrobial resistance in ICUs between 1994-2000.

The surveillance program has been described previously.3 In brief, each institution agreed to test 100 consecutive gram-negative aerobic isolates recovered from ICU patients. Organisms were identified to the species level. Susceptibility tests were performed with a standardized microtiter minimal inhibitory concentration (MIC) panel (Microscan MKD MIC, Dade International MicroScan, Sacramento, Calif). Participating laboratories used National Committee for Clinical Laboratory Standards–recommended validation of MICs with American Type Culture Collection test strains.3 Piperacillin/tazobactam and cefepime were added to the panel in 1996 and 1998, respectively. Hospitals were categorized based on teaching status and bed size. National fluoroquinolone consumption data were obtained from IMS HEALTH Retail and Provider Perspective (Plymouth Meeting, Pa) in conjunction with its MIDAS database. The data presented are from nonduplicate isolates that we evaluated independently of the research sponsor.

Study variables were subjected to univariate descriptive analysis. Non-normal data were rank transformed before application of parametric testing when appropriate. Pearson and Spearman rank order intercorrelational analyses of year of observation were used to compare resistance rates and fluoroquinolone use. All statistical analyses were performed using SAS release 8.0 for IBM PC Windows and SAS Version 6.14 for mainframe computers (SAS Institute Inc, Cary, NC).

A total of 35 790 isolates were collected during 1994-2000; 77 to 117 ICUs participated per year, representing 43 states plus the District of Columbia. Approximately half of the hospitals repeatedly took part in this program. The majority of institutions were teaching hospitals (85%) and were intermediate to large sized (200-500 beds [59%]; >500 beds [38%]).

Pseudomonas aeruginosa was the most frequently isolated organism (23%) followed by Enterobacter species (14.0%), K pneumoniae (13.6%), and Escherichia coli (11.3%). The remaining 38.1% of isolates included Acinetobacter species (5.8%), Serratia marcescens (5.4%), Stenotrophomonas maltophilia (4.3%), Proteus mirabilis (3.6%), Citrobacter species (2.9%), and Morganella morganii (0.9%).

Most isolates were cultured from the respiratory tract (51.5%), urine (16.0%), blood (13.8%), or wounds (11.8%). Pseudomonas aeruginosa was the most frequent isolate from the respiratory tract (31.6%) and wounds (24.9%); K pneumoniae was the most common blood isolate (20.8%); and E coli was the most frequent urine isolate (35.5%).

Antimicrobial agents could be grouped into 3 broad categories based on overall in vitro activity (Table 1). While the activity of most agents decreased 6% or less over the study period, the overall susceptibility to ciprofloxacin decreased steadily from 86% in 1994 to 76% in 2000. Ciprofloxacin maintained excellent in vitro activity against E coli, but showed reduced activity against other organisms, especially P aeruginosa. Ciprofloxacin resistance did not differ significantly in teaching vs nonteaching hospitals or in hospitals with more than 500 beds vs hospitals with 500 beds or less. The decline in ciprofloxacin susceptibility was associated significantly with increasing national use of fluoroquinolones during the study period (Figure 1). Resistance to ciprofloxacin was associated with cross-resistance to other broad-spectrum antimicrobial agents (Table 2).

Table Graphic Jump LocationTable 1. Antimicrobial Susceptibility Rates for All and for the 4 Most Common Species of Gram-Negative Bacilli, Intensive Care Unit Surveillance, 1994-2000*
Figure. Fluoroquinolone Use and Resistance Rates in Pseudomonas aeruginosa and Gram-Negative Bacilli
Graphic Jump Location
National fluoroquinolone use data were obtained from IMS HEALTH Retail and Provider Perspective (Plymouth Meeting, Pa). The increasing rates of ciprofloxacin resistance correlate with the steadily increasing fluoroquinolone use (r = 0.976, P<.001 for P aeruginosa; r = 0.891, P = .007 for gram-negative bacilli; r = 0.958, P<.001 for years of observation). The 1990-1993 data points represent composite susceptibility3 and fluoroquinolone use for those 4 years.
Table Graphic Jump LocationTable 2. Examples of Antimicrobial Cross-resistance Among Selected Gram-Negative Bacilli, Intensive Care Unit Surveillance,1994-2000*

We examined susceptibility data for gram-negative bacilli isolated from ICU patients in 43 states and the District of Columbia. As in 1990-1993,3 amikacin (90%) and imipenem (89%) were the most active agents. Our findings (Table 1) suggest that there is an overall chance of 10% or greater that an infecting gram-negative bacillus in an ICU patient will be resistant to any single agent, which may help to explain the trend to increased use of multidrug regimens for initial empirical therapy of suspected nosocomial infection.16

Our 1990-1993 data identified the rising incidence of ceftazidime-resistant K pneumoniae and Enterobacter species, suggesting the widespread presence of plasmid-mediated extended-spectrum β-lactamases (ESBLs) and of hyperproducers of type 1 chromosomal β-lactamases, respectively. From 1990-1993 to 1994-2000, there was a further decline in the ceftazidime susceptibility for K pneumoniae (93% vs 87%) and Enterobacter species (67% vs 63%), similar to the findings of the most recently published Centers for Disease Control and Prevention National Nosocomial Infections Surveillance data from 1994-1998.6

The most alarming trend detected in the current study was the decreasing activity of ciprofloxacin. The overall susceptibility to ciprofloxacin among aerobic gram-negative bacilli declined from 89% in 1990-19933 to 86% in 1994 to 76% in 2000. The most notable reductions in ciprofloxacin susceptibility were seen with P aeruginosa (89% in 1990-19933 to 68% in 2000). The declines in activity of ciprofloxacin correlate with a greater than 2.5-fold increase in use of quinolones (ciprofloxacin, levofloxacin, ofloxacin)—popular agents for treating community-acquired pneumonia, urinary tract infections, and skin and soft tissue infections—over the past 10 years (Figure 1).

Cross-resistance has been observed with the newer fluoroquinolones against ciprofloxacin-resistant gram-negative bacteria.7 While there have been suggestions that fluoroquinolone resistance also is related phenotypically to the presence of ESBLs,8,9 implying that fluoroquinolone resistance could be driven by cephalosporin use, fluoroquinolone resistance has not been linked genetically to resistance to other classes of drugs. However, plasmid-mediated fluoroquinolone resistance has been described recently,10 and fluoroquinolone use may select for bacteria with heightened antibiotic efflux capability.11 Thus, ciprofloxacin resistance may be associated with limited treatment options for other classes of agents, as observed in our study (Table 2) and other studies.8,12

As with any large national surveillance study, these findings have limitations. Molecular typing of organisms was not performed; therefore, we cannot exclude the possibility of epidemics or clonal spread of bacteria. However, the large number of study sites makes it unlikely that epidemics in an individual ICU influenced our results. In addition, our analysis did not include or adjust for potentially important confounders such as case mix, prior antibiotic exposure, mechanical ventilation, or ICU length of stay. Although actual antibiotic consumption data for the ICUs under study would allow for a more targeted correlation of drug exposure and resistance, ecologic population data such as ours can provide important support for analyses of resistance trends.13 Population-based antibiotic use data may be especially important for the fluoroquinolones since the extensive use of these agents in the community setting may affect hospital resistance rates. In fact, fluoroquinolones are the only class of antibiotics for which resistance has been similar in the ICU and non-ICU setting.2

In conclusion, our findings add to prior surveillance efforts by (1) providing a decade-long perspective, (2) presenting results from 35 790 isolates from ICUs nationwide, (3) documenting the rising incidence of antibiotic-resistant gram-negative bacilli, and (4) comparing these results with fluoroquinolone use trends. This work expands on other research, including a recent international study in 5 European countries documenting a high incidence of reduced antibiotic susceptibility among gram-negative bacteria.14 We have focused on ciprofloxacin resistance because of the increasingly frequent use of fluoroquinolones for treatment of urinary tract infections and pneumonia in the community and hospital setting. Fluoroquinolones that are not affected by currently circulating resistance mechanisms need to be developed to conserve this class of agents.15 In the meantime, ongoing surveillance and more judicious use of fluoroquinolone antibiotics16 will be necessary to limit this downward trend in susceptibility.

Archibald L, Phillips L, Monnet D, McGowan JE, Tenover F, Gaynes R. Antimicrobial resistance in isolates from inpatients and outpatients in the United States: increasing importance of the intensive care unit.  Clin Infect Dis.1997;24:211-215.
Fridkin SK, Steward CD, Edwards JR.  et al.  Surveillance of antimicrobial use and antimicrobial resistance in United States hospitals: project ICARE phase 2.  Clin Infect Dis.1999;29:245-252.
Itokazu GS, Quinn JP, Bell-Dixon C, Kahan FM, Weinstein RA. Antimicrobial resistance rates among aerobic gram-negative bacilli recovered from patients in intensive care units: evaluation of a national postmarketing surveillance program.  Clin Infect Dis.1996;23:779-784.
Gales AC, Jones RN, Turnidge J, Rennie R, Ramphal R. Characteristics of Pseudomonas aeruginosa isolates: occurrence rates, antimicrobial susceptibility patterns, and molecular typing in the global SENTRY antimicrobial surveillance program, 1997-1999.  Clin Infect Dis.2001;32:S146-S155.
Edmond MB, Wallace SE, McClish DK, Pfaller MA, Jones RN, Wenzel RP. Nosocomial bloodstream infections in United States hospitals: a three-year analysis.  Clin Infect Dis.1999;29:239-244.
 National Nosocomial Infections Surveillance (NNIS) system report data summary from January 1992-April 2000, issued June 2000  Am J Infect Control.2000;28:429-448.
Tankovic J, Bachoual R, Ouabdesselam S, Boudjadja A, Soussy CJ. In-vitro activity of moxifloxacin against fluoroquinolone-resistant strains of aerobic gram-negative bacilli and Enterococcus faecalis J Antimicrob Chemother.1999;43(suppl B):S19-S23.
Wiener J, Quinn JP, Bradford PA.  et al.  Multiple antibiotic-resistant Klebsiella and Escherichia coli in nursing homes.  JAMA.1999;281:517-523.
Paterson DL, Mulazimoglu L, Casellas JM.  et al.  Epidemiology of ciprofloxacin resistance and its relationship to extended-spectrum beta-lactamases production in Klebsiella pneumoniae isolates causing bacteremia.  Clin Infect Dis.2000;30:473-478.
Martinez-Martinez L, Pascual A, Jacoby GA. Quinolone resistance from a transferable plasmid.  Lancet.1998;351:797-799.
Kohler T, Epp SF, Curty LK, Pechere JC. Characterization of MexT, the regulator of the MexE-MexF-OprN multidrug efflux system of Pseudomonas aeruginosa J Bacteriol.1999;181:6300-6305.
Lautenbach E, Strom BL, Bilker WB, Patel JB, Edelstein PH, Fishman NO. Epidemiological investigation of fluoroquinolone resistance in infections due to extended-spectrum beta-lactamase-producing Escherichia coli and Klebsiella pneumoniae Clin Infect Dis.2001;33:1288-1294.
Walson JL, Marshall B, Pokhrel BM, Kafle KK, Levy SB. Carriage of antibiotic-resistant fecal bacteria in Nepal reflects proximity to Kathmandu.  J Infect Dis.2001;184:1163-1169.
Hanberger H, Garcia-Rodrigues JA, Gobernado M.  et al.  Antibiotic susceptibility among aerobic gram-negative bacilli in intensive care units in 5 European countries.  JAMA.1999;281:67-71.
Hooper DC. Mechanisms of action and resistance of older and newer fluoroquinolones.  Clin Infect Dis.2000;31:S24-S28.
Gonzales R, Bartlett JG, Besser RE.  et al.  Principles of appropriate antibiotic use for treatment of acute respiratory tract infections in adults: background, specific aims, and methods.  Ann Intern Med.2001;134:479-486.

Figures

Figure. Fluoroquinolone Use and Resistance Rates in Pseudomonas aeruginosa and Gram-Negative Bacilli
Graphic Jump Location
National fluoroquinolone use data were obtained from IMS HEALTH Retail and Provider Perspective (Plymouth Meeting, Pa). The increasing rates of ciprofloxacin resistance correlate with the steadily increasing fluoroquinolone use (r = 0.976, P<.001 for P aeruginosa; r = 0.891, P = .007 for gram-negative bacilli; r = 0.958, P<.001 for years of observation). The 1990-1993 data points represent composite susceptibility3 and fluoroquinolone use for those 4 years.

Tables

Table Graphic Jump LocationTable 1. Antimicrobial Susceptibility Rates for All and for the 4 Most Common Species of Gram-Negative Bacilli, Intensive Care Unit Surveillance, 1994-2000*
Table Graphic Jump LocationTable 2. Examples of Antimicrobial Cross-resistance Among Selected Gram-Negative Bacilli, Intensive Care Unit Surveillance,1994-2000*

References

Archibald L, Phillips L, Monnet D, McGowan JE, Tenover F, Gaynes R. Antimicrobial resistance in isolates from inpatients and outpatients in the United States: increasing importance of the intensive care unit.  Clin Infect Dis.1997;24:211-215.
Fridkin SK, Steward CD, Edwards JR.  et al.  Surveillance of antimicrobial use and antimicrobial resistance in United States hospitals: project ICARE phase 2.  Clin Infect Dis.1999;29:245-252.
Itokazu GS, Quinn JP, Bell-Dixon C, Kahan FM, Weinstein RA. Antimicrobial resistance rates among aerobic gram-negative bacilli recovered from patients in intensive care units: evaluation of a national postmarketing surveillance program.  Clin Infect Dis.1996;23:779-784.
Gales AC, Jones RN, Turnidge J, Rennie R, Ramphal R. Characteristics of Pseudomonas aeruginosa isolates: occurrence rates, antimicrobial susceptibility patterns, and molecular typing in the global SENTRY antimicrobial surveillance program, 1997-1999.  Clin Infect Dis.2001;32:S146-S155.
Edmond MB, Wallace SE, McClish DK, Pfaller MA, Jones RN, Wenzel RP. Nosocomial bloodstream infections in United States hospitals: a three-year analysis.  Clin Infect Dis.1999;29:239-244.
 National Nosocomial Infections Surveillance (NNIS) system report data summary from January 1992-April 2000, issued June 2000  Am J Infect Control.2000;28:429-448.
Tankovic J, Bachoual R, Ouabdesselam S, Boudjadja A, Soussy CJ. In-vitro activity of moxifloxacin against fluoroquinolone-resistant strains of aerobic gram-negative bacilli and Enterococcus faecalis J Antimicrob Chemother.1999;43(suppl B):S19-S23.
Wiener J, Quinn JP, Bradford PA.  et al.  Multiple antibiotic-resistant Klebsiella and Escherichia coli in nursing homes.  JAMA.1999;281:517-523.
Paterson DL, Mulazimoglu L, Casellas JM.  et al.  Epidemiology of ciprofloxacin resistance and its relationship to extended-spectrum beta-lactamases production in Klebsiella pneumoniae isolates causing bacteremia.  Clin Infect Dis.2000;30:473-478.
Martinez-Martinez L, Pascual A, Jacoby GA. Quinolone resistance from a transferable plasmid.  Lancet.1998;351:797-799.
Kohler T, Epp SF, Curty LK, Pechere JC. Characterization of MexT, the regulator of the MexE-MexF-OprN multidrug efflux system of Pseudomonas aeruginosa J Bacteriol.1999;181:6300-6305.
Lautenbach E, Strom BL, Bilker WB, Patel JB, Edelstein PH, Fishman NO. Epidemiological investigation of fluoroquinolone resistance in infections due to extended-spectrum beta-lactamase-producing Escherichia coli and Klebsiella pneumoniae Clin Infect Dis.2001;33:1288-1294.
Walson JL, Marshall B, Pokhrel BM, Kafle KK, Levy SB. Carriage of antibiotic-resistant fecal bacteria in Nepal reflects proximity to Kathmandu.  J Infect Dis.2001;184:1163-1169.
Hanberger H, Garcia-Rodrigues JA, Gobernado M.  et al.  Antibiotic susceptibility among aerobic gram-negative bacilli in intensive care units in 5 European countries.  JAMA.1999;281:67-71.
Hooper DC. Mechanisms of action and resistance of older and newer fluoroquinolones.  Clin Infect Dis.2000;31:S24-S28.
Gonzales R, Bartlett JG, Besser RE.  et al.  Principles of appropriate antibiotic use for treatment of acute respiratory tract infections in adults: background, specific aims, and methods.  Ann Intern Med.2001;134:479-486.

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