Vopni R, Voice A, de Riese CS et al: Use of antimicrobial-coated catheters in preventing catheter-associated urinary tract infections and bacteriuria: a meta-analysis for clinicians. Urol Pract 2021; 8: 705.

Between 15% and 25% of all patients require indwelling urinary catheters at some stage during their hospital stay, posing a significant risk of catheter-associated urinary tract infections (CAUTIs).¹ As a medical intervention, primitive catheters have been used to treat urinary retention since as early as 3,000 BCE. Early catheters were composed of oiled reeds and palm leaves, and progressed to metals such as copper, tin, gold and even lead.² Refinement improved flexibility, and then the introduction of rubber catheters in the 18th century was a major step toward patient comfort. Another important step in the evolution of catheters was made by Frederic Foley, who first developed a self-retaining balloon catheter in the late 1920s. He demonstrated this to the AUA in the mid 1930s and published a paper in 1937.³

In the ongoing quest of reducing the risks of CAUTIs, Ludwig Guttmann advocated sterile catheterization, and Jack Lapides recommended intermittent catheterization.² However, CAUTIs remain a significant burden on morbidity, mortality and health care costs. While considered preventable, CAUTIs account for 35% of nosocomial infections, resulting in more than 13,000 deaths each year, which is a major concern to physicians and hospitals alike.⁴ Direct treatment costs due to CAUTI are estimated to be greater than $350 million each year, which are not eligible for reimbursement by Medicare or Medicaid.⁵ Suboptimal catheter materials are considered the main cause of biofilm formation, leading to bacteriuria and severe infection.¹ In this context, we performed a meta-analysis of prospective and randomized studies on coated indwelling bladder catheters published over the last 2 decades (between January 2000 and December 2020).⁶ Figure 1 shows the flowchart using the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines for this review analysis. Many studies were published, but only 15 fulfilled the main scientific inclusion criteria (prospective and randomized; see table). Figure 2 illustrates the forest plot of CAUTI incidence comparison between noncoated (control) and coated (experimental) groups.

Figure 1. PRISMA flowchart with detailed description of identification, screening, eligibility and included steps performed for article collection.

Figure 2. Forest plot of study CAUTI incidence rates between noncoated (control) and coated (experimental) groups with odds ratio analysis including 95% confidence intervals.

To qualify for the diagnosis of CAUTI, a patient must have urinary tract infection (UTI)-associated symptoms and ≥10³ colony-forming units/ml in the absence of other infection sources besides the catheter.⁷ It is well documented in the literature that bacteriuria occurs within 24-48 hours after placing an indwelling catheter, but screening for or treatment of asymptomatic bacteriuria is not recommended. Because the incidence of bacteriuria is easier to track, many studies have reported on bacteriuria only rather than symptomatic UTIs.

Additionally, the definitions of UTI and CAUTI have varied in the literature over time, and even the Centers for Disease Control and Prevention (CDC) guidelines have caused confusion by inconsistently including asymptomatic bacteriuria.⁸ It has been estimated that 10%-20% of patients with bacteriuria develop episodes of symptomatic UTIs with the risk of sepsis, suggesting that any improvements in bacteriuria rates should help in reducing the incidence of symptomatic CAUTIs and other serious sequelae. As a result of extensive research, we now understand that bacteriuria is facilitated by a bacterial biofilm on the surface of catheters and the bladder mucosa. Biofilm is a conglomerate of bacteria embedded in a 3-dimensional structure of polysaccharides, proteins and lipids resistant to mechanical stress such as urine flow and bladder irrigation.⁹

Different antimicrobial catheter coatings have been studied for their ability to prevent or inhibit biofilm formation, encrustation and thus bacteriuria. Many antimicrobial coatings interfere with bacterial metabolism and disrupt bacterial colonization. Silver as catheter coating is particularly well studied due to its ability to kill microbes at low concentrations without causing resistance. One of the main factors impacting the tolerability of silver-nanoparticle coating is its slow release of ions, which otherwise could cause an extensive inflammatory response of the bladder wall. In nitrofurazone-coated catheters, nitrofural inhibits protein synthesis for various bacterial enzymes even at low concentrations, and despite years of use, bacterial resistance remains rare. Furthermore, noble metal alloys (such as gold, copper, palladium and platinum) have proven to be effective against biofilm as single-substance coating as well as combined, with synergistic effects.¹⁰ Other new coating substances have been studied over recent years: for instance, JUC^® spray, a nanotechnological substance with promising antimicrobial features in preventing biofilm formation. Furthermore, CyanoCoating, graphene and, most promising, bacteriocins from lactobacillus have been reported with excellent bactericidal and anti-biofilm in vitro properties, although only very limited clinical data are currently available.

Our meta-analysis showed evidence that catheter coating may be advantageous in lowering the incidence of bacteriuria and CAUTIs. However, the limited number of prospective randomized studies with limited statistical power as well as the heterogeneity between studies have been the main barriers for establishing catheter coating technology in routine clinical practice. Therefore, future prospective randomized clinical trials will have to focus on standardized clinical criteria in definitions of bacteriuria/CAUTI combined with excellent numbers of participating patients (to improve statistical power) in order to validate superiority of coated catheters.