Catheter-associated urinary tract infections: diagnosis and prophylaxis☆
Introduction
Catheter-associated urinary tract infection (CAUTI) is the most common nosocomial infection in hospitals and nursing homes world-wide with more than one million episodes in the United States alone [1], [2]. Although most CAUTIs are asymptomatic [3], rarely extend hospitalization and add only US$ 500–1000 to the direct costs of acute care hospitalization [4], asymptomatic infections often precipitate unnecessary antimicrobial therapy. Although the costs of catheter-associated urinary tract infections are not as high as for example a deep surgical site infection or a nosocomial pneumonia, CAUTIs are a cause for concern as they are a major reservoir of resistant pathogens [5], [6]. Numerous studies have documented a high prevalence of resistant pathogens in CAUTI and the association between nosocomial CAUTI and surgical site infections has been made [7].
Section snippets
Diagnosis
In a study conducted almost 20 years ago, Stark and Maki [8] showed that in the absence of antibiotics, even one microorganism per ml would predictably multiply over time to reach 105–106 microorganisms per ml in the catheterized urinary tract. They showed that 103 microorganisms per ml is a sensitive cut-off for CAUTI. In non-catheterized patients, by convention, 105 organisms per ml of urine is used as a criterion for diagnosis of UTI but for symptomatic women with UTIs, a much lower colony
Pyuria
Pyuria is widely used as a criterion for diagnosing urinary tract infections in non-catheterized patients. However, in a large prospective study of more than 750 patients [10], pyuria was found to be most useful in predicting CAUTI in patients with UTI due to Gram-negative pathogens while CAUTI caused by large numbers of yeasts and enterococci or staphylococci were less significantly associated with pyuria. This is thought to be due to less urinary tract inflammation elicited by these
Symptoms
Symptoms are also not reliable for the diagnosis of CAUTI. Although many guidelines [13], [14] make the distinction between “symptomatic CAUTI” and asymptomatic bacteriuria in the management of CAUTI, we were unable to demonstrate a difference in presence of fever or symptoms related to the urinary tract in catheterized patients with and without CAUTI, in a large prospective study [4]. The catheter can itself be the source of symptoms as was noted in that study in which the proportion of
Pathogenesis
The entry of a urinary catheter bypasses the normal host defences at the meatus and allows the entry of pathogens into the bladder. The presence of a foreign body also allows for the formation of a biofilm, which is a conduit for pathogens to multiply and cause infection. It has been postulated that there are two main routes for CAUTI. Firstly, the extraluminal route: this could be either early at the time of catheter insertion due to inadequate antisepsis or contamination, or late due to
Risk factors
At least five prospective studies [22], [23], [24], [25], [26] have conducted multivariate analysis of the risk factors associated with CAUTI with daily urine cultures to detect all CAUTIs in large numbers of patients. These studies were found to have remarkably similar results. The most important risk factors have been prolonged catheterization and being female. Other risk factors identified have included catheterization outside the sterile environment of the operating room, being on a urology
Prevention
The best way of preventing a CAUTI is to remove the catheter or to avoid its use. All studies have shown the duration of catheterization as a significant risk factor for nosocomial CAUTI [22], [23], [24], [25]. A recent study by Saint et al. [27] showed that a number of physicians at various levels are unaware that their patients are catheterized. Catheters have been described as a “one-point restraint” for hospitalized patients [28], and in a classic editorial nearly half a century ago, Beeson
Silver-coated catheters
Silver is a well-known antiseptic with a long history, as an antiseptic rather than an antibiotic and the risk of generating antibiotic resistance would be expected to be low. Argyrism is a potential concern that has limited the use of silver on the internal coating of catheters and possibly limited its efficacy. There are a number of studies that have evaluated silver-coated catheters including silver oxide catheters and silver alloy catheters. Silver oxide catheters were found to have no
Antibiotic coated catheters
Antibiotic coated catheters using a combination of rifampicin and minocycline [45] have been used and were found to be effective in preventing nosocomial intravenous catheter related infections as well [46]. The rifampicin-minocycline catheter was most effective in preventing CAUTI caused by Gram-positive rather than Gram-negative bacteria thus limiting its practical efficacy. The concern has been in the development of antibiotic resistance. In many parts of the world, where Mycobacterium
Novel technologies
Other technologies that appear promising on the horizon include the use of urethral stents [47]. Even further on the horizon perhaps are technologies, which translate bench research into cell-cell communications which would inhibit the formation of the biofilm in the first place. Quorum sensing is an area of intense research interest. A quorum sensing inhibitor has been shown in vivo to be effective in preventing the development of a biofilm by Staphylococcus epidermidis [48] and this could
Conclusion
There are clearly many challenges that face researchers and clinicians working in the field of CAUTI. Foremost among these must be the prevention of these infections. Effective interventions to prevent CAUTI will doubtless help to reduce the reservoir of resistant pathogens in the intensive care units, wards and long-term care facilities. This will be a critical step in the battle against antibiotic resistance.
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Presented in part at the Surgical Infections: Prevention and Management Conference held on 29–30 May 2003 in Moscow, Russia.