New strategies to prevent catheter-associated urinary tract infections

Catheter-associated urinary tract infection (CAUTI) is the most common health-care-associated infection worldwide. Although not all cases of bacteriuria result in clinical infection, several hundred thousand episodes of CAUTI occur each year in the USA alone. The milieu in which the catheter is placed is highly conducive to bacterial colonization, biofilm formation on the catheter surface, and inevitable catheter-associated bacteriuria. A multitude of novel methods of CAUTI prevention have been described, including established approaches that are routinely recommended, such as the use of a secured, closed, silicone urinary catheter drainage system that mimics normal voiding, and newer strategies focusing on biocompatible catheter materials that cause minimal host inflammatory response and retard biofilm formation. Much recent research has focused on modification of the catheter surface by either coating or impregnation with antimicrobials or antiseptics. However, clinical trials that analyse cost-effectiveness and rates of antimicrobial resistance are awaited. More recently, innovative use of iontophoresis, vibroacoustic stimulation, bacterial interference and bacteriophage cocktails has been reported.     

Positive urine cultures: A major cause of inappropriate antimicrobial use in hospitals?

INTRODUCTION

Urine specimens are among the most common samples submitted for culture to microbiology laboratories. The objectives of the present study were to describe the indications for obtaining urine cultures in a cohort of hospitalized patients, and to determine the appropriateness of antimicrobial therapy in response to urine culture results.

METHODS:

The study was performed at a teaching hospital with an adjoining long-term care facility from June 1 to July 31, 2006. The medical records of nonpregnant adult patients with and without bacteriuria were reviewed. A symptomatic urinary tract infection was defined as the presence of bacteriuria in a patient with fever or urinary symptoms; asymptomatic bacteriuria was defined as bacteriuria without urinary symptoms and no infection evident at another site.

RESULTS:

Medical records of 335 eligible patients (64% male; mean age 68 years) were reviewed, including all 137 with bacteriuria, and 198 with negative urine cultures. In total, 51% of the urine specimens were obtained from an indwelling urinary catheter, and 28% were voided urine samples. Confusion (57%) and fever (36%) were the most common indications noted for obtaining the urine cultures. Only 34 patients (25% of those with positive urine cultures) met the criteria for a symptomatic urinary tract infection; 67 (49%) had asymptomatic bacteriuria and 36 (26%) had infection at a nonurinary site. Of those with asymptomatic bacteriuria, 64% received antimicrobial therapy for a total of 347 days. Confused patients with asymptomatic bacteriuria were more likely to be treated than were bacteriuric patients without altered mental status (OR 1.8, 95% CI 1.2 to 4.1; P=0.03).

CONCLUSIONS:

Urine cultures are frequently obtained from hospitalizedpatients,evenintheabsenceofurinarysymptoms.Asymptomatic bacteriuria is often treated in these patients, and accounts for a substantial burden of inappropriate antimicrobial use in hospitals. Effective strategies to improve urine culture ordering and antimicrobial utilization in hospitals need to be implemented.     

A prospective microbiologic study of bacteriuria in patients with chronic indwelling urethral catheters

Bacteriuria is common in chronically catheterized patients and is associated with both acute and chronic complications. Of 605 consecutive weekly urine specimens from 20 chronically catheterized patients, 98% contained bacteria at high concentrations and 77% were polymicrobial. The mean interval between new episodes of bacteriuria was 1.8 weeks. Most species of bacteria caused five to seven new episodes of bacteriuria per 100 weeks of catheterization. Even though access to the catheter lumen was similar, the duration of bacteriuric episodes varied greatly by species. Of the episodes of bacteriuria caused by nonenterococcal gram-positive cocci, greater than 75% lasted less than one week. Mean durations of episodes of bacteriuria due to Escherichia coli, Proteus mirabilis, and Pseudomonas aeruginosa were four to six weeks, whereas those due to Providencia stuartii averaged 10 weeks and ranged up to 36 weeks. Thus, the very high prevalence of bacteriuria--virtually 100%--was a result of a high incidence caused by many different species combined with the prolonged residence of some gram-negative bacilli in the catheter and urinary tract.     

Clinical complications of urinary catheters caused by crystalline biofilms: something needs to be done

This review is largely based on a previous paper published in the journal Spinal Cord. The care of many patients undergoing long‐term bladder catheterization is complicated by encrustation and blockage of their Foley catheters. This problem stems from infection by urease‐producing bacteria, particularly Proteus mirabilis. These organisms colonize the catheter forming an extensive biofilm; they also generate ammonia from urea, thus elevating the pH of urine. As the pH rises, crystals of calcium and magnesium phosphates precipitate in the urine and in the catheter biofilm. The continued development of this crystalline biofilm blocks the flow of urine through the catheter. Urine then either leaks along the outside of the catheter and the patient becomes incontinent or is retained causing painful distension of the bladder and reflux of urine to the kidneys. The process of crystal deposition can also initiate stone formation. Most patients suffering from recurrent catheter encrustation develop bladder stones. P. mirabilis establishes stable residence in these stones and is extremely difficult to eliminate from the catheterized urinary tract by antibiotic therapy. If blocked catheters are not identified and changed, serious symptomatic episodes of pyelonephritis, septicaemia and endotoxic shock can result. All types of Foley catheters including silver‐ or nitrofurazone‐coated devices are vulnerable to this problem. In this review, the ways in which biofilm formation on Foley catheters is initiated by P. mirabilis will be described. The implications of understanding these mechanisms for the development of an encrustation‐resistant catheter will be discussed. Finally, the way forward for the prevention and control of this problem will be considered.     

Bacterial biofilms and catheters: A key to understanding bacterial strategies in catheter-associated urinary tract infection

Despite major technological improvements in catheter drainage systems, the indwelling Foley catheter remains the most common cause of nosocomial infection in medical practice. By approaching this common complicated urinary tract infection from the perspective of the biofilm strategy bacteria appear to use to overcome obstacles to produce bacteriuria, one appreciates a new understanding of these infections. An adherent biofilm of bacteria in their secretory products ascends the luminal and external surface of the catheter and drainage system from a contaminated drainage spigot or urethral meatus into the bladder. If the intraluminal route of bacterial ascent is delayed by strict sterile closed drainage or addition of internal modifications to the system, the extraluminal or urethral route assumes greater importance in the development of bacteriuria, but takes significantly longer. Bacterial growth within these thick coherent biofilms confers a large measure of relative resistance to antibiotics even though the individual bacterium remains sensitive, thus accounting for the failure of antibiotic therapy. With disruption of the protective mucous layer of the bladder by mechanical irritation, the bacteria colonizing the catheter can adhere to the bladder's mucosal surface and cause infection. An appreciation of the role of bacterial biofilms in these infections should suggest future directions for research that may ultimately reduce the risk of catheter-associated infection.     

Bacteriuria in pregnancy

The urinary tract undergoes profound physiologic and anatomic changes during pregnancy that facilitate the development of symptomatic urinary tract infections in women with bacteriuria. While the adverse effects of asymptomatic bacteriuria on maternal and fetal health continue to be debated, it is clear that asymptomatic bacteriuria is the major risk factor for developing symptomatic urinary tract infection and that symptomatic infections are associated with significant maternal and fetal risks. Because the majority of symptomatic urinary tract infections develop in women with bacteriuria earlier in pregnancy, treatment of bacteriuria is undertaken to prevent symptomatic infections. All women should be screened at the first antenatal visit, which is reliably and inexpensively done with a dipstick culture. Short-course therapy is as effective as prolonged therapy and should be followed with a repeat culture to document clearing of the bacteriuria. Failure to eliminate bacteriuria with repeated therapy or recurrence with the same organism is indicative of renal parenchymal infection or a structural abnormality. All women with persistent bacteriuria or recurrent infection should have follow-up cultures and a complete urologic evaluation after delivery.     

The presence of antibody-coated anaerobic bacteria in asymptomatic bacteriuria during pregnancy.

Quantitative anaerobic culture of urine samples obtained from 593 pregnant women by suprapubic bladder aspiration was performed to establish the involvement of anaerobic bacteria in asymptomatic urinary tract infections. The fluorescent antibody (FA) test was applied to the sediments of bladder aspirates to determine the site of infection. Anaerobic bacteriuria (greater than or equal to 10(4) microorganisms/ml of urine) was found in 34 patients, of whom five were FA-positive. These anaerobes were identified as Lactobacillus minutus, Veillonella parvula (two patients). Clostridium putrefaciens, and Peptostreptococcus anaerobius. Aerobic bacteriuria (greater than 10(4) microorganisms/ml of urine) was detected in 27 patients, of whom 13 were FA-positive. In 10 women with mixed aerobic/anaerobic bacteriuria, no FA-positive bacteria were found. The finding of FA-positive anaerobes may indicate that these organisms are involved in silent renal infection.     

Infecciones del tracto urinario nosocomiales

Nosocomial urinary tract infections (UTI) are mainly related to urinary catheterisation. In this paper we review the pathogenic mechanisms, particularly the route by which the microorganisms colonise the urinary tract, their adhesion ability, and their capacity to form biofilms, and are related not only to the microorganism but also to the type of urinary catheter. The aetiology of catheter related UTI is variable, and multiresistant microorganisms are often isolated, making empirical antibiotic therapy complex. Clinical findings are frequently atypical, and its diagnosis is difficult. The therapeutic management of catheter-related UTI should be stratified according to the type of UTI: asymptomatic bacteriuria should not be habitually treated, but patients with septic shock should receive a broad spectrum antibiotic. In this review, the value of the different preventive measures are discussed.     

Preventing catheter-related bacteriuria: should we? Can we? How?

Up to 25% of hospitalized patients undergo urinary catheterization, and about 5% develop bacteriuria each day of catheterization. Catheter-related bacteriuria is associated with increased morbidity and mortality. We performed an evidence-based synthesis of the literature on preventing catheter-associated urinary tract infections (UTIs) to develop recommendations for clinicians. Catheterization should be avoided when not required and when needed, should be terminated as soon as possible. Use of suprapubic and condom catheters may be associated with a lower risk of UTI than use of urethral catheters. Aseptic catheter insertion and a properly maintained closed drainage system are crucial to reducing the risk of bacteriuria. Instillation of antimicrobial agents into the bladder or urinary drainage bag and rigorous meatal cleansing seem to be of little benefit. Use of urinary catheters coated with silver alloy may reduce the risk of UTI. Systemic antimicrobial drug therapy seems to prevent UTIs, but primarily for patients catheterized for 3 to 14 days. Antibiotic drug prophylaxis is especially valuable in patients undergoing transurethral resection of the prostate or renal transplantation. Using these methods, urinary catheter-associated UTI can often be prevented for weeks, but not longer terms.     

Prevention of catheter-associated urinary tract infection

PURPOSE OF REVIEW: The underlying cause of catheter-associated urinary tract infection is biofilm formation by uropathogens on the urinary catheter. Biofilm is a relatively new concept in medicine, and current measures to prevent biofilm formation are inadequate. Considerable work is being done in this area, but little clinical progress has been made. The purpose of this review is to analyze recent publications concerning prevention of catheter-associated urinary tract infection. RECENT FINDINGS: Several recent studies have elucidated aspects of biofilm formation in catheter-associated urinary tract infection. Other researchers are working on methods to disrupt biofilm formation on catheter surfaces. At the same time, the magnitude of the problem of catheter-associated urinary tract infection has increased awareness of the effectiveness of basic infection control measures. A modern approach to infection control may include computerized ordering systems that minimize unnecessary days of catheterization. Finally, consumption of cranberry juice products and bacterial interference are two novel approaches to urinary tract infection prevention. SUMMARY: Biofilm-disrupting strategies offer promise for the future but have little immediate applicability. Implementation of infection control measures to improve catheter function and remove unnecessary catheters can be done at the present time. In general, prevention of catheter-associated urinary tract infection remains an elusive goal. More basic research at the level of pathogenesis is needed so that novel strategies can be designed.     

Amdinocillin treatment of catheter-associated bacteriuria in rabbits

The effect of the beta-lactam antibiotic, amdinocillin, on the bacterial biofilm adherent to the Foley catheter surface, the bacterial microcolonies attached to the urinary bladder mucosa, and on planktonic bacteria in the urine was studied in a rabbit model of the closed urinary catheter drainage system. Progressively increasing the dose of antibiotic in this experimental catheter-associated urinary tract infection model first eliminated the bacterial population adherent to the bladder mucosa and then the planktonic population in the urine. The bacterial biofilm on the Foley catheter could be eradicated only by the highest dose of antibiotic (400 mg/kg). Scanning electron microscopy showed a gradual deterioration of bacterial biofilm and reduction in bacterial numbers with increasing antibiotic dosages. These data suggest that antibiotics used in short-term catheterization may reduce the serious sequelae associated with catheter-related infections by clearing the potentially dangerous bladder mucosal bacterial populations and urine planktonic bacteria.     

Catheter associated urinary tract infections in neurology and neurosurgical units

OBJECTIVE: Catheter associated bacteriuria is the most common infection acquired in hospitals. The objective of the study was (1) to study the incidence of bacteriuria following indwelling urethral catheterization in patients with short-term vs long-term catheterization (2) to define the antibiotic resistance pattern among these isolates so that the study can provide guidelines for choosing an effective antibiotic against infections in catheterized patients. METHODS: This is a prospective study carried out over a period of 18 months in Neurology/Neurosurgical patients who had indwelling catheters for > or =48 h. RESULTS: In this study, 68 out of 800 (8.5%) adult inpatients acquired urinary tract infection following indwelling bladder catheterizations. The risk was significantly higher for female, elderly patients, critically ill and patients on prolonged catheterization. Among the bacterial pathogens, Escherichia coli was the commonest organism isolated (32.9%) followed by Pseudomonas sp. (15.1%) and Staphylococcus aureus (12.3%). Candida sp. comprised 13.7% of all isolates. Among Gram negative bacterial pathogens maximum number of isolates were sensitive to Amikacin (sensitivity of 42%). All Gram positive organisms were however sensitive to Vancomycin. CONCLUSIONS: Our results provide guidelines for choosing salvage therapy against hospital resistant strains causing infection in catheterized patients. However, antibiotics seem to prevent urinary tract infections but primarily in patients catherized for short duration, i.e. 3-14 days and not in patients with long-term catheterization.     

Effect of confounding in the association between circumcision status and urinary tract infection

OBJECTIVES: To estimate the impact of confounding in the association between circumcision status and urinary tract infection from epidemiological factors, sample collection, and health-seeking behaviors in the first year of life. METHODS: Beginning with the assumption that true urinary tract infection occurred equally regardless of circumcision status, a Markov model incorporating the differences in the rates of prematurity, of urine collection, of false positive urine specimens, and of health-seeking behaviors in infant boys based on circumcision status was developed. Using this model, the rates of false-positive urine cultures, asymptomatic bacteriuria, and true urinary tract infection detected in the first year of life were estimated and contrasted. Error of the model was estimated using Monte Carlo simulations. RESULTS: Keeping the incidence of true urinary tract infection constant between groups, the factors included in the model could account for urinary tract infection being diagnosed 4.27 times more frequently in non-circumcised males under a year of age. CONCLUSIONS: Previously reported differences in the rate of urinary tract infection by circumcision status could be entirely due to sampling and selection bias. Until clinical studies adequately control for sources of bias, circumcision should not be recommended as a preventive for urinary tract infection.     

Water or antiseptic for periurethral cleaning before urinary catheterization: A randomized controlled trial

BACKGROUND: Despite a lack of empiric data to support the practice, traditionally, antiseptic solutions have been used to clean the periurethral area before inserting an indwelling catheter. The purpose of this study was to compare urinary colonization rates of subjects whose periurethral area was cleaned with water versus chlorhexidine 0.1% before the insertion of an indwelling urinary catheter. METHODS: Obstetric patients who required urinary catheterization as part of their routine care were randomly assigned to either the "water" or "chlorhexidine" group with a sealed envelope. A sterile specimen of urine was collected 24 hours after insertion of the catheter. RESULTS: Of the 436 patients (86.2%) with complete data (water group, 219; antiseptic group, 217), 38 (8.7%) had urinary tract bacteriuria >10(6) cfu/L. Rates of urinary tract infection were similar in each group (water group, 8.2%; antiseptic group, 9.2%; odds ratio 1.13; 95% confidence interval 0.58-2.21). CONCLUSION: The practice of periurethral cleaning with an antiseptic did not decrease the rates of bacteriuria in this population and is probably not useful.     

Urine sampling in ambulatory women: midstream clean-catch versus catheterization

We conducted a study to determine if there were any significant differences in urinalyses or urine cultures obtained by midstream clean-catch (MSCC) urine sampling in comparison with in-and-out catheterization (CATH). One hundred five women with symptoms suggestive of a urinary tract infection were studied prospectively. Each woman had a MSCC urine sample obtained initially, followed by a CATH sample. The MSCC and CATH urine samples were analyzed and compared for urine culture, leukocyte esterase, nitrites, microscopic bacteriuria, and pyuria. Of the 105 patients, 42 (40%) had a culture-proven urinary tract infection. The concordance rates between MSCC and CATH urine cultures, nitrites, leukocyte esterase, significant microscopic bacteriuria, and pyuria were 96%, 94%, 93%, 90%, and 90%, respectively. There were no statistically significant differences between MSCC and CATH sensitivities, specificities, or positive or negative predictive values for any urinalysis variable (leukocyte esterase, nitrites, significant microscopic bacteriuria, or pyuria). We conclude that if proper MSCC technique is used, the differences between MSCC and CATH urinalyses or urine cultures do not appear to be significant in the majority of ambulatory women without active vaginal bleeding who present with symptoms suggestive of a urinary tract infection.     

Natural history of bacteriuria in women with primary biliary cirrhosis and the effect of antimicrobial therapy in symptomatic and asymptomatic groups.

Primary biliary cirrhosis (PBC) patients have an increased incidence of recurrent urinary tract infection compared with patients with other chronic liver diseases. The course of significant asymptomatic and symptomatic bacteriuria in women with PBC was evaluated: consecutive patients were screened for bacteriuria at their outpatient appointments. Bacteriuric patients who were asymptomatic (n = 21) were randomised to receive antimicrobial therapy (n = 11), or no therapy (n = 10). Bacteriuric patients who were symptomatic (n = 13) were treated. All were followed up by weekly dipslide examination of urine. The course of bacteriuria in the 13 symptomatic and 11 asymptomatic treated patients was similar in terms of the medium interval between successive infective episodes (three and four weeks respectively), the number of relapses (six and seven) and reinfections (14 and 18). Most untreated asymptomatic patients became abacteriuric spontaneously but became reinfected with a different organism during the study period. A separate group of 24 PBC patients with no previous bacteriologically proved urinary tract infection was followed weekly in a similar fashion: seven (29%) became bacteriuric for two to four weeks during a three month period. This study suggests that treatment of recurrent bacteriuric episodes in PBC patients does not alter the natural history of their infection. The long term implication of periodically infected urine in these patients is currently unknown.     

Once-daily irrigation of long-term urethral catheters with normal saline. Lack of benefit

Urinary incontinence is often managed with a long-term urethral catheter after other methods have failed. Such urethral catheterization is associated with polymicrobial bacteriuria, catheter obstruction, fever, bacteremia, urinary tract stones, and death. Periodic catheter irrigation is a common but untested management procedure intended to prevent catheter obstruction, fevers, and/or bacteremia. To evaluate this technique, we performed a randomized crossover trial comparing ten weeks of once-daily normal saline irrigation with ten weeks of no irrigation in 32 long-term catheterized women. The incidence of catheter obstructions and febrile episodes and the prevalence and species of bacteriuria were similar whether examined as completed crossover patients (N = 23) or as partially completed trials (N = 9). Once-daily irrigation with normal saline of long-term urethral catheters is a time-consuming and costly procedure that is unlikely to have an impact on the morbidity associated with such catheters.     

Catheter-associated urinary tract infection is rarely symptomatic: a prospective study of 1,497 catheterized patients

BACKGROUND: Catheter-associated urinary tract infection (CAUTI) is the most common nosocomial infection, accounting for more than 1 million cases each year in US hospitals and nursing homes. OBJECTIVE: To define the clinical features of CAUTI. SETTING AND PATIENTS: A university hospital; 1,497 newly catheterized patients. DESIGN: Every day that the catheter was in place, a quantitative urine culture and urine leukocyte count were obtained, and the patient was queried by a research worker regarding symptoms. To more precisely define the role of CAUTI in patients' symptoms, a subset of 1,034 patients, 89 of whom developed CAUTI with more than 10(3) colony-forming units per milliliter, who did not have another potentially confounding site of infection besides the urinary tract, was analyzed. OUTCOME MEASURES: Presence of fever, symptoms commonly associated with community-acquired urinary tract infection, and peripheral leukocytosis. RESULTS: There were 235 new cases of nosocomial CAUTI during the study period. More than 90% of the infected patients were asymptomatic; only 123 infections (52%) were detected by patients' physicians using the hospital laboratory. In the subset analysis, there were no significant differences between patients with and without CAUTI in signs or symptoms commonly associated with urinary tract infection-fever, dysuria, urgency, or flank pain-or in leukocytosis. Only 1 of the 235 episodes of CAUTI that were prospectively studied was unequivocally associated with secondary bloodstream infection. CONCLUSIONS: Whereas CAUTIs are a major reservoir of antibiotic-resistant organisms in the hospital, they are rarely symptomatic and infrequently cause bloodstream infection. Symptoms referable to the urinary tract, fever, or peripheral leukocytosis have little predictive value for the diagnosis of CAUTI.     

Urinary tract infection in long-term-care facility residents.

Urinary tract infection is the most frequent bacterial infection in residents of long-term-care facilities. Most infections are asymptomatic, with a remarkable prevalence of asymptomatic bacteriuria of 15%-50% among all residents. The major reasons for this high prevalence are chronic comorbid illnesses with neurogenic bladder and interventions to manage incontinence. Prospective, randomized, comparative trials of therapy and no therapy for asymptomatic bacteriuria among nursing home residents have repeatedly documented that antimicrobial treatment had no benefits. However, there is substantial diagnostic uncertainty in determining whether an individual with a positive urine culture has symptomatic or asymptomatic infection when there is clinical deterioration and there are no localized findings. In the noncatheterized resident, urinary infection is an infrequent source of fever but may not be definitively excluded. The use of antimicrobials for treatment of urinary infection is part of the larger concern about appropriate antimicrobial use in long-term-care facilities and the impacts of the selective pressure of antimicrobials on colonization and infection with resistant organisms.     

Practical management of catheter-associated UTIs

In the long-term catheterized elderly, damage to the epithelial wall is primarily responsible for bladder infections, due to the presence of the catheter as a foreign body and its frequent manipulations. The presence of bacteriuria, a classic sign of infection in the non-catheterized patient, is of little diagnostic importance in the long-term catheterized patient, since it is both permanent and inevitable. Routine preventive measures--eg, frequent catheter changes, prophylactic antibiotics--are of no value. Other measures are worth considering and, if instituted, will reduce the frequency of severe complications from long-term catheterization and improve quality of life.