Burn the bridge! Infections, antibiotic-resistant pathogens linked to catheters in dialysis settings
Dialysis population will almost double by end of decade
The increasing use of catheters to deliver hemodialysis care is spurring a rise in both infections and antibiotic resistant pathogens, health care epidemiologists reported recently in San Diego at the Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC).
Hemodialysis requires frequent access to the patient’s blood stream, and vascular access has been called the "Achilles’ heel" of hemodialysis care.1 Three types of vascular access predominate: AV (arteriovenous) fistulas, AV grafts, and catheters. Catheters often are "bridge" devices, used to fill the gap between the start of dialysis treatments (often an emergency) to when the patient’s AV fistula or AV graft has matured and is ready for use. Catheters are generally not recommended as long-term devices, as they tend to have higher rates of infection and thrombosis. However, in many cases, dialysis centers are not aggressively pursuing better options for both vascular access and antibiotic therapy, speakers at an ICAAC session underscored.
"Clearly, we shouldn’t be using hemodialysis catheters as much as we do," said Mark Rupp, MD, a medical epidemiologist at the University of Nebraska Medical Center in Omaha. "We need to try to push patients toward getting AV fistulas and grafts as much as possible. If we do dialyze through a catheter, we should be using cuffed, tunneled catheters. And I think that your cutoff for using [regular uncuffed catheters] should probably be somewhere in the neighborhood of two to three weeks. If you’ve got a patient you think is going to get dialyzed for more than a couple or three weeks, you should be pushing toward using tunneled catheters."
Exacerbating the problem is a demographic trend that shows a steady increase in the patient population undergoing dialysis.
"This problem is going to continue to get larger," he said, noting that projections indicate the current total of about 400,000 patients with end-stage renal disease will increase to some to 700,000 by the end of the decade. "This is largely fueled by the amount of hypertension and diabetes in an increasingly aging population."
In outlining the problem, Rupp cited emerging data from the new dialysis surveillance system by the Centers for Disease Control and Prevention.2 (See Healthcare Infection Prevention, October 2002, at www.HIConline.com.) In addition to ongoing infection problems associated with vascular access, the CDC is finding a diverse and deadly variety of outbreaks in the dialysis setting. Overall, the CDC is finding that vascular access infections are common, but the risk of acquiring infection varies substantially among different vascular access types.
"Infection is the second-leading cause of death behind cardiovascular disease in our hemodialysis patients, and it is responsible for somewhere around 15% to 35% of all caused mortality," Rupp said. "Vascular access [infections] result in about four days of hospitalization per patient per year at a cost of about a billion dollars per year in the United States." Complicating prevention efforts, the line between endogenous and exogenous reservoirs for infecting organisms is often blurred, Rupp said.
"It’s difficult to figure out [by] which of these routes the organisms gain access to the catheters, but by far the most important are via the skin and also via the hub," he said. "Very rarely do you have hematogenous seeding of the catheters or a contaminated infusate."
The key step in the pathogenesis of the infections is the ability of the pathogens to adhere and proliferate on the surface of the catheter, he added. "Effective treatment often requires removal of these catheters either to go to a de novo exchange or via guidewire exchange," Rupp said. "[In] any patient who has a hemodialysis catheter infection — where they are obviously septic or have a very significant systemic inflammatory response syndrome — the catheter should come out. Also, you should have a very high suspicion of removal of these catheters if there is a tunnel tract infection."
About one third of dialysis patients are dialyzed through AV fistulas and about 41% through grafts made up of Gore-Tex or polytypofluoroethylene. That leaves some 25% of dialysis patients on tunneled and cuffed catheters, and 3% being dialyzed through noncuffed catheters, he said. "The number of patients that are being dialyzed through catheters is rising dramatically," he said. "Back in 1995, about 10% to 12% [of patients were] dialyzed through catheters. Currently in our centers, somewhere around 25% to 30% are being dialyzed through catheters. The reason that this is so important, is that the risk of bacteremia is hugely driven by patients who are being dialyzed through catheters."
In the CDC dialysis surveillance system, the rate of bacteremia expressed in 100 patient-months — which is essentially the percent of patients in any given month who experience a bacteremia — is 1% for AV fistulas; about 5% for cuffed catheters; and 9% for noncuffed catheters. "Catheters are very much more prone to have bacteremia associated with them," he said. "The ramifications of this are profound for our patients in terms of morbidity, mortality and cost, but also in terms of our society, in the promotion of antibiotic resistance."
The major infecting pathogen in dialysis is Staph-ylococcus aureus, which leads to the use of vancomycin for treatment of its methicillin-resistant (MRSA) strains. Historically, vancomycin has been the drug of choice in the setting because it can be given conveniently at one dose a week. However, clear signs of emerging resistance to vancomycin have appeared in the last decade. Most of the cases of vancomycin-intermediate S. aureus (VISA), which began occurring in the mid-1990s, have been in dialysis patients.
As of June 2002, eight patients with clinical infections caused by VISA, which is partially resistant to vancomycin, have been confirmed in the United States. Of even greater concern, the first completely vancomycin-resistant strain of S. aureus (VRSA) occurred in June 2002. The isolate was found on a swab obtained from a catheter exit site of a 40-year-dialysis patient. If VRSA is to arise and establish a threatening niche on the health care landscape, it likely will be via dialysis patients.
More than a coincidence
"I don’t think it’s a coincidence that many of the first cases of vancomycin intermediate susceptible Staph aureus were defined in dialysis patients, and the first case of a high-level resistant strain was defined in a dialysis patient," Rupp said.
According to current antibiotic prescribing guidelines, vancomycin may be used for empiric treatment for febrile hemodialysis patients with an unknown infection site pending susceptibility data if there is a high prevalence of methicillin-resistant pathogens in that dialysis unit; or the patient has a history of colonization or infection with methicillin-resistant pathogens, said Loreen Herwaldt, MD, medical epidemiologist at the University of Iowa Hospital and Clinics in Iowa City.
Other indications for vancomycin include initial treatment for infected prosthetic access; treatment of known beta lactam-resistant pathogens; treatment of patients with serious beta lactam allergy; and for prophylaxis during placement of foreign bodies such as catheters for dialysis in a facility with a high prevalence of methicillin-resistance pathogens, she said.
"Vancomycin should not be used in dialysis patients just because the dosing interval is convenient," Herwaldt told ICAAC attendees. "It also should not be used for routine prophylaxis of patients who are treated with peritoneal dialysis or hemodialysis."
An alternative therapy is administration of a first-generation cephalosporin. "Gentamicin should be used until culture results are available except if the patient is septic, has a history of MRSA or beta lactam allergy, or a prosthetic access," she said. "Then vancomycin is the better choice"
With problems emerging with antibiotic resistance and overuse of catheters, adherence to basic infection control measures in dialysis becomes all the more important, she noted. "It’s important to know that we can not only select resistant organisms; we can transmit them," Herwaldt said. "I can also tell you from my peritoneal dialysis unit at home, we now have evidence of numerous strains of susceptible Staph aureus being shared by a number of the patients and health care workers in that unit."
Increased use of alcohol-based hand hygiene products — now being heavily emphasized throughout the health care system — may be an important infection control adjunct measure in dialysis units as well, she added.
1. RenalWEB. Dialysis topics. Functioning vascular access device. At www.renalweb.com/topics/out_vascaccess/vascaccess.htm.
2. Tokars JI, Miller E, Stein G. New national surveillance system for hemodialysis-associated infections: Initial results. Am J Infect Control 2002; 30:288-295.