Healthcare-Associated Infections in Patients With Spinal Cord Injury
Rabih O. Darouiche
About 262,000 Americans suffer from spinal cord injury and its complications, with 12,000 new cases accruing each year (1). Although it remains unknown if the incidence of spinal cord injury has changed over the years, it is estimated that about 40 cases occur in the United States per million persons (1). However, the number of patients living with spinal cord injury is expected to continue to rise owing to the increase in their life expectancy that is almost similar to that in the able-bodied population. Most cases of spinal cord injury are traumatic, most notably due to motor vehicle accidents, gunshot wounds, falls, contact sports, diving injuries, earthquakes, and acupuncture (2, 3 and 4). Nontraumatic causes include spinal tumors, infection, transverse myelitis, and iatrogenic events, especially perioperative hypotension (5). Although the vast majority of cases of spinal epidural abscess are bacterial and are caused mostly by Staphylococcus aureus (6), a variety of other microorganisms, including agents of tuberculosis (7), brucellosis (8), actinomycosis (9), neurocisticercosis (10) and shistosomiasis (11) as well as fungi-like Candida (12) and Aspergillus (13) species, and HIV, may also be causes of spinal epidural abscess (14).
Healthcare-associated infections in patients with spinal cord injury have unique attributes and commonly require multidisciplinary management. Healthcare-associated infections in spinal cord-injured persons are also a major cause of morbidity and often are lethal. Compared to those who do not become infected, patients with spinal cord injury who develop healthcare-associated infections have lower functional improvements, shorter survival, and a higher likelihood for prolonged future hospitalization (15,16).
The three most prevalent infections in patients with spinal cord injury affect the urinary tract, respiratory tract, and the skin and soft tissues, in the form of decubiti, with or without involvement of the underlying bone. The main objectives of this chapter are to: (a) address the factors that predispose to healthcare-associated infections in relation to the time of injury; (b) delineate the interrelated pathogenesis and microbiology, unusual clinical manifestations, problematic diagnosis, and difficult prevention of infections involving the urinary tract, the respiratory tract, and the skin and soft tissues with or without involvement of the underlying bone; and (c) assess the spread, colonization, and infection by multiresistant microorganisms.
FACTORS THAT PREDISPOSE TO HEALTHCARE-ASSOCIATED INFECTIONS
Patients with spinal cord injury are predisposed to healthcare-associated infections both in the acute and the chronic settings after injury (Table 56-1). The administration of high doses of glucocorticosteroids immediately after traumatic injury is associated with a significant increase in respiratory and total infections (17). Immediately after the spinal cord injury, patients are admitted to the hospital for management of injuries to the spinal cord and possibly other bodily organs. Not only do some injured patients initially require acute intensive care that poses its own risks for acquiring infection, but all subsequently undergo in-patient rehabilitation for up to few months (5). Critically ill patients and those residing in specialized spinal cord injury units have a particularly high risk of developing infections with resistant microorganisms, including extended-spectrum beta-lactamase (ESBL)-producing gram-negative bacilli, methicillin-resistant S. aureus (MRSA), and vancomycin-resistant enterococci (VRE).
Furthermore, patients with spinal cord injury frequently have sustained concurrent wounds of the neck, chest, and abdomen that may require surgical intervention, thereby imposing additional risks for postoperative infections. The majority of patients during the period of spinal cord shock suffer from neurogenic bladder that necessitates catheter drainage, often leading to development of urinary tract infection. Likewise, the insertion of central vascular access for administration of fluids, blood and blood products, and medications or for hemodynamic monitoring may cause bloodstream infection. Patients with high cervical injury usually require mechanical ventilation and can develop ventilator-associated pneumonia.
Furthermore, patients with spinal cord injury frequently have sustained concurrent wounds of the neck, chest, and abdomen that may require surgical intervention, thereby imposing additional risks for postoperative infections. The majority of patients during the period of spinal cord shock suffer from neurogenic bladder that necessitates catheter drainage, often leading to development of urinary tract infection. Likewise, the insertion of central vascular access for administration of fluids, blood and blood products, and medications or for hemodynamic monitoring may cause bloodstream infection. Patients with high cervical injury usually require mechanical ventilation and can develop ventilator-associated pneumonia.
TABLE 56-1 Factors that Predispose to Healthcare-Associated Infections | ||||||||||||||||||||||||||||
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Although the likelihood of developing infection appears to be the highest in the acute postinjury period, the vast majority of infections occur long after the spinal cord injury. This finding is attributed to the fact that many patients sustain spinal cord injury when still young and have an almost normal life expectancy. Since most patients with spinal cord injury chronically rely on bladder catheters for urinary drainage, urinary tract infection is the most common infection long after the injury. Second in frequency are infections associated with decubiti. Patients with high cervical lesions are especially predisposed to both tracheostomy- and endotracheal tube-related respiratory tract infections. Surgical management of the chronic sequelae of spinal cord injury can be complicated by surgical site infections. Injury to the spinal cord can result in immunosuppressive effects, particularly in patients with high-level injury that causes alteration to the sympathetic nervous system or the hypothalamic-pituitary-adrenal axis (18). Possible immunologic deficits include impaired antibody synthesis (18), reduced phagocytic activity (19), and aberrant accumulation of glucocorticoids and norepinephrine in the blood and spleen (20).
URINARY TRACT INFECTIONS
Pathogenesis and Epidemiology
Accounting for 25% to 50% of all infections, urinary tract infections are the most common healthcare-associated infection in patients with spinal cord injury (21). The two unique factors that predispose this population to urinary tract infection include bladder catheterization and urinary stasis. The incidence of urinary tract infection appears to be the same in patients with spinal cord injury who have either an indwelling transurethral or a suprapubic bladder catheter (22). Since intermittent bladder catheterization predisposes to urinary tract infection less than indwelling bladder catheterization, the former approach is advised whenever feasible. Unfortunately, only one-fifth of patients continue to practice this method of bladder drainage (23). Although the sterile technique of bladder catheterization can theoretically be safer, at least in hospitalized patients, than the clean technique, both catheterization techniques can introduce pathogens into the urinary tract. Urinary stasis impairs the naturally occurring mechanisms that protect the urinary tract from infection, including the washout effect of voiding and the phagocytic capacity of bladder epithelial cells. Multiplication of bacteria in the urine and invasion of host tissues are promoted in the presence of reduced bladder emptying, increased residual urine, and high bladder pressure.
Although more than 90% of episodes of urinary tract infection in this population seem to involve only the lower urinary tract, serious complications can still arise secondary to such infections. Ascending infection of the urinary tract may evolve in the presence of vesicoureteral reflux or as a consequence of manipulations aimed at emptying the bladder. Taking into consideration that renal failure was once the leading cause of death in this population, kidney infection with loss of renal function is particularly worrisome. Additionally, urinary tract infection can be associated with a number of anatomic changes, such as renal calculi (occupying the bladder, ureters, or kidneys), bladder diverticulae and fibrosis, penile and scrotal fistulas, epididymoorchitis, and abscesses. The frequency of these anatomic changes depends on the type and the duration of bladder drainage; for instance, these changes are most commonly detected in patients with indwelling bladder catheters.
The vast majority of episodes of urinary tract infection in patients with spinal cord injury are caused by commensal bowel flora, primarily gram-negative bacilli and enterococci. The microbiology of microorganisms residing in the bladder can be affected by patients’ gender, the source of pathogens (i.e., healthcare-associated vs. community-associated), and the method of urinary drainage. For instance, Klebsiella pneumoniae is a very common cause of urinary tract infection in hospitalized patients, whereas Escherichia coli and the enterococci cause more than two-thirds of cases of urinary tract infection in female patients undergoing intermittent bladder catheterization. The presence of condom catheters increases the likelihood of colonizing the urethra and the perineal skin with Pseudomonas, Klebsiella, and other gram-negative bacilli. As in able-bodied subjects, the presence of renal calculi in patients with spinal cord injury suggests etiology by urease-producing bacteria. Spinal cord injury units are no different from other types of specialized care units as to the occurrence of outbreaks of urinary tract infection due to multiresistant gram-negative bacilli. Increasing antibacterial usage has been associated with occurrence of candiduria (24). Polymicrobial growth is detected in almost half of positive urine cultures obtained from patients with spinal cord injury, particularly those with chronic indwelling urethral catheters (25).
Clinical Manifestations
Urinary tract infection may manifest differently in patients with spinal cord injury than in the general population. For instance, infected patients with spinal cord injury may not complain of dysuria, frequency, and urgency—symptoms that usually exist in able-bodied patients with urinary tract infection. Furthermore, suprapubic and flank pain or tenderness are not felt in insensate patients. More common manifestations of urinary tract infection in patients with spinal cord injury include worsening spasm, increasing dysreflexia, and change in voiding habits. Fever is usually, but not always, present.
Diagnosis
Diagnosing urinary tract infection in patients with spinal cord injury can be problematic for several reasons. First, by masking urinary-specific symptoms, absent sensations
constitute the single most important obstacle in diagnosing this infection in this population. Second, the unusual manifestations of urinary tract infection in these patients are nonspecific and may be caused by a variety of other infectious or noninfectious conditions, including osteomyelitis beneath decubiti, ingrown toe nails, and heterotopic bone ossification. Third, bacteriuria, the cornerstone for diagnosing urinary tract infection, is nonspecifically prevalent in this population. Bacteriuria is most frequent in patients who have chronic indwelling bladder catheters, as cultures of randomly obtained urine samples yield bacterial growth in more than 90% of instances. Even patients who undergo intermittent bladder catheterization have a 70% likelihood of being bacteriuric. Most cases of bacteriuria in patients with spinal cord injury represent asymptomatic bladder colonization. Although asymptomatic bladder colonization can progress to symptomatic infection, often it does not. Fourth, the finding of pyuria, which can reflect inflammation of the uromucosal lining and signal the transition from bladder colonization to symptomatic urinary tract infection, is not specific for infection. Pyuria can be caused by a variety of noninfectious conditions, including catheterinduced trauma, renal stone, recent urologic procedure, and interstitial nephritis.
constitute the single most important obstacle in diagnosing this infection in this population. Second, the unusual manifestations of urinary tract infection in these patients are nonspecific and may be caused by a variety of other infectious or noninfectious conditions, including osteomyelitis beneath decubiti, ingrown toe nails, and heterotopic bone ossification. Third, bacteriuria, the cornerstone for diagnosing urinary tract infection, is nonspecifically prevalent in this population. Bacteriuria is most frequent in patients who have chronic indwelling bladder catheters, as cultures of randomly obtained urine samples yield bacterial growth in more than 90% of instances. Even patients who undergo intermittent bladder catheterization have a 70% likelihood of being bacteriuric. Most cases of bacteriuria in patients with spinal cord injury represent asymptomatic bladder colonization. Although asymptomatic bladder colonization can progress to symptomatic infection, often it does not. Fourth, the finding of pyuria, which can reflect inflammation of the uromucosal lining and signal the transition from bladder colonization to symptomatic urinary tract infection, is not specific for infection. Pyuria can be caused by a variety of noninfectious conditions, including catheterinduced trauma, renal stone, recent urologic procedure, and interstitial nephritis.
Because of these potential problems in establishing a diagnosis, particularly when based on patients’ prediction (26), there exists no universally accepted definition of symptomatic urinary tract infection in patients with spinal cord injury. A commonly used definition of symptomatic urinary tract infection in these patients requires the presence of significant bacteriuria (≥105 colony-forming units [CFU]/mL), pyuria (>10 WBC/high power field [hpf] for spun urine), and fever (>100°F) plus more than one of the following signs and symptoms—(a) suprapubic or flank discomfort, (b) bladder spasm, (c) change in voiding habits, (d) increased spasticity, and (e) worsening dysreflexia—provided that no other potential etiologies for these clinical manifestations can be identified (27,28). Most healthcare providers tend to distinguish upper from lower urinary tract infection based on clinical manifestations and laboratory rather than imaging findings. For example, the presence of high fever (>102°F), chills, systemic toxicity, high-grade leukocytosis (>20,000 per mm3), and/or leukocyte casts in urinary sediment supports the presence of pyelonephritis.
Prevention
Mechanical Approaches Since the indwelling transurethral and suprapubic catheters pose a higher risk of infection than intermittent bladder catheterization, the latter method of bladder drainage should always be considered, barring any anatomic or functional constraints. Increasing the frequency of intermittent bladder catheterization can decrease the risk of urinary tract infection. Although the technique of clean nonsterile intermittent self-catheterization is considered rather safe for use by outpatients, sterile intermittent catheterization is implemented by most hospitals owing to the fear of healthcare-associated introduction of multiresistant and virulent microorganisms into the urinary tract. In patients with persistent or recurrent urinary tract infections, the urinary tract should be investigated for anatomic abnormalities (including abscess, stone, obstruction, and stricture) and functional alterations (such as vesicoureteral reflux, high residual volume of urine in bladder, and elevated bladder pressure). The use of drugs and surgical procedures to reduce bladder pressure and aid bladder emptying can help alleviate the risk of urinary tract infection. Recent evidence suggested that the use of a catheter-securing device has the potential for preventing symptomatic urinary tract infection in patients with spinal cord injury (29).
Antimicrobial Approaches Treatment of asymptomatic bacteriuria with bladder instillation of antibiotic solutions may alleviate bacteriuria temporarily. However, this may result in the emergence of antibiotic resistance and there is no evidence that this practice prevents clinical urinary tract infection. Studies that examined the administration of systemic antimicrobial agents in patients with spinal cord injury (30, 31 and 32) have yielded either conflicting or disappointing results in terms of efficacy and emergence of antibiotic resistance. In general, systemic antimicrobial use is discouraged for treatment of asymptomatic bacteriuria in patients with spinal cord injury (33,34,35). Exceptions may include patients with (a) enlarging struvite stones associated with urea-splitting microorganisms, such as Proteus mirabilis and Providentia stuartii (36); (b) conditions that enhance the likelihood of developing significant complications from having asymptomatic bacteriuria, such as premature birth in pregnant women; and (c) recurrent episodes of upper urinary tract infection that are complicated by sepsis or other clinical complications, particularly if the recurrent infections are caused by the same microorganism. It is important to note that, in general, antimicrobial treatment of asymptomatic bacteriuria in women with diabetes mellitus is probably not warranted (37). Although Cochrane reviews suggested that the use of cranberry supplements (38) or methenamine hippurate (39) could be beneficial in some clinical scenarios, the applicability of these approaches in the population of patients with spinal cord injury is of unclear value (40, 41 and 42). The clinical efficacy of antimicrobial-impregnated bladder catheters has not been tested in the population of patients with spinal cord injury, or for that matter, in patients with chronic indwelling bladder catheters. Preprocedure systemic antibiotic prophylaxis is generally indicated before urologic procedures, including urodynamics, and the administered antibiotic regimen is best chosen based on results of urine cultures and antimicrobial susceptibility tests obtained before the procedure.
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