Clinical Review

Antibiotic Therapy and Bacterial Resistance in Patients With Spinal Cord Injury

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The length of treatment of urinary tract infections with antibiotics is controversial, because extended antibiotic therapy may lead to the acquisition of antibiotic resistance. This study suggests that exposure to longer antibiotic treatment courses may lead to increased antimicrobial resistance in patients with spinal cord injury.


Nosocomial urinary tract infections (UTIs) are often associated with significant morbidity, mortality, and health care costs.1,2 Patients with spinal cord injury (SCI) often have indwelling or intermittent urinary catheters and are prone to have asymptomatic bacteriuria and UTIs. As a result, they frequently receive antimicrobial therapy and have a higher prevalence of antibiotic resistant urinary tract isolates compared with patients without SCI.3-5 Unfortunately, data are lacking to provide guidance for optimal treatment and duration for UTIs in patients with SCI.

Many studies have evaluated patient propensity for development of antibiotic resistance in UTIs. Age > 65 years, use of a urinary catheter, previous hospitalization, and prior antimicrobial use have been identified as common risk factors.6-8 Waites and colleagues evaluated antimicrobial resistance of urinary tract organisms in outpatients with SCI and found that 33% of urinary cultures isolated multidrug-resistant microorganisms. The authors demonstrated a relationship between antimicrobial resistance and broad spectrum and prophylactic use of antibiotics.3,9

This study sought to determine the incidence of resistance acquisition by comparing susceptibility profiles of the same organisms isolated from the same patient in consecutive episodes of bacteriuria. Given that prior antimicrobial use was identified as a common risk factor for antibiotic resistance in previous reports, this study also sought to determine patterns of antibiotic use in patients with SCI at the VA North Texas Health Care System (VANTHCS) in Dallas, Texas, to evaluate whether any correlations between antibiotic use and resistance acquisition exist. A secondary objective included identification of other risk factors that may increase acquisition of resistance.

Study Design
This study was a retrospective chart review approved by the Institutional Review Board at the VANTHCS. Since computerized charting was available beginning July 2003, the VA Computerized Patient Record System was queried to identify male or female adult (aged ≥ 18 years) veterans admitted to the SCI inpatient unit between July 1, 2003, and December 31, 2009, for review. Patients who had an ICD-9 code consistent with paraplegia, tetraplegia, or quadriplegia and 2 consecutive urine cultures that isolated the same organism within 6 months of each other were included. Males with a diagnosis of epididymitis or prostatitis were excluded.

The following data were collected for analysis: gender, age, weight, height, American Spinal Injury Association (ASIA) Impairment Scale Grades (A-E), duration of hospitalization in the SCI unit, the presence and type of urinary catheter, microbiology and antibiotic regimen, past medical history, previous antibiotic history, comorbidities, and concomitant drug therapy. The presence and type of urinary catheter was determined by the primary investigator and verified by the physician who oversaw care of patients with SCI.

All antimicrobial sensitivity testing was performed via the Microscan (Microscan Systems, Inc., Renton, WA) automated testing system. Acquisition of antibiotic resistance was defined as an increase of at least 2 dilutions in the breakpoint or change on the susceptibility panel from Susceptible (S) to Resistant (R) on the repeat urine culture.

Analysis of Resistance
Continuous parameters were reported as mean (standard deviation [SD]), and discrete parameters were reported as a percentage. Analyses of variance (ANOVA) were computed to evaluate the difference in the mean of the continuous parameters. The Mann-Whitney U test replaced the ANOVA when a dependent variable was not normally distributed. Associations between pairs of discrete parameters were tested with the Pearson chi-square test. Logistic regression analyses were performed to determine the associations between potential risk factors (age, ASIA grade, antibiotic duration, class of antibiotic) and antibiotic resistance. The study alpha was α < .05. All analyses were performed with SPSS 20.0 for Windows.

Three hundred fifty-five veterans admitted to the SCI unit during the study period were initially identified. Of those, 269 did not meet inclusion criteria and were excluded. The most common reason for exclusion was absence of a second positive urine culture with isolation of the same organism. Other reasons for exclusion included no urine cultures completed while admitted to the SCI unit or no diagnosis of SCI.

A total of 86 subjects, mean aged 56.7 years (SD, 14.2), were included in the study. Subjects were primarily men (93%) with a mean body mass index of 25.5 (SD, 7). Most of the subjects were classified Complete on the ASIA scale, meaning no motor strength or sensation below their neurologic level of injury (ASIA A; 38.4%), followed by Sensory Incomplete (ASIA B; 25.6%), Motor Incomplete-Low Muscle Strength (ASIA C; 16.3%), Motor Incomplete-High Muscle Strength (ASIA D; 14%), and Normal (ASIA E; 1.2%).

Both groups (resistance and no resistance) had similar baseline characteristics, and no differences were found for the following characteristics: ASIA grade, length of stay (LOS), presence of or control of diabetes, and presence of an indwelling urinary catheter (Table 1). However, veterans in the resistance group were significantly older than those in the no resistance group (aged 61 years vs aged 54 years; P = .03) and spent more time housed in the SCI unit with a mean LOS of 141 days vs 84 days (P = .049). Urinary pathogens developed resistance in 32 patients (37.2%, resistance group), and 54 patients (62.8%, no resistance group) did not.


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