Answer: Dialysis patients are at increased risk for infection for many reasons. This article will focus on infections in hemodialysis patients and will not address peritonitis or other infections related to peritoneal dialysis. Patients with chronic kidney disease have abnormalities in their immune system which impair their ability to fight infection. Although the white blood cell count in the typical laboratory testing profile may be normal, the dialysis patient's white blood cells (which are the primary line of defense against infection) typically do not function normally.

There are two major types of white blood cells: neutrophils and lymphocytes. Neutrophils are primarily involved in defending against bacterial infections but bacteria may survive in dialysis patients long enough to produce infections that would not occur in normal individuals. This is because neutrophils' ability to ingest and destroy bacteria is weakened in the setting of kidney disease.

Infections by bacteria called Staphylococcus are particularly common. Staphylococcus is a normal inhabitant of the skin but, given the decreased resistance to infection by Staphylococcus that often occurs in patients with kidney disease, these bacteria are much more likely to invade the body. Once these bacteria have access to the blood stream, they frequently spread to bones, joints and the heart, causing potentially lethal destruction of these tissues.

Lymphocytes are primarily involved in protection against infections caused by viruses and fungi. In patients with kidney disease, the activation of lymphocytes to a state where they are most effective in protecting against these infections is impaired, resulting in an increased incidence of viral and fungal infections. Viral infections include simple things like influenza, but also serious conditions such as shingles and hepatitis. Dialysis patients are not only more prone to developing all of these types of viral infections but, when these infections do occur, they tend to be more severe.

As a result, vaccines which decrease the severity of viral infections such as influenza and hepatitis B are strongly recommended in dialysis patients. Fungal infections are more common in dialysis patients than in the general population and need to be dealt with promptly before they become serious.

The most common type of fungal infection is the yeast infection which typically affects the vaginal area in women, the feet (athlete's foot), skin folds, and nail beds (onychomycosis). Although relatively easy to treat with currently available antibiotics, yeast can be dangerous if it spreads to catheters (hemodialysis or peritoneal dialysis catheters), where the infection can be almost impossible to eliminate unless the catheter is removed. Onychomycosis also is somewhat more difficult to eradicate than other fungal infections and generally requires several months of antifungal therapy.

Patients with kidney failure are more prone to developing urinary tract infections (UTIs) for a number of reasons. First of all, the mere act of passing urine tends to flush out the urinary tract of infectious agents so they cannot gain a foothold and cause problems. Once the kidneys fail and the production of urine is decreased, this normal flushing action is gone. UTIs usually are caused by bacteria which normally inhabit the bowel and spread to the urinary tract by local extension.

Patients with renal failure may have other urinary tract abnormalities which make them more prone to developing UTIs. These include cysts in the kidney which can become infected, obstruction of the urinary tract which impairs drainage and causes further stagnation of urine, and bladder reflux which causes urine in the bladder to move backwards into the kidneys and increases the chance that an infection in the bladder will spread to the upper urinary tract where it is more serious and likely to spread into the blood stream.

Infections in a hemodialysis vascular access () are amonurinary tract infections (g the most common causes for hospitalization in dialysis patients and can cause serious complications. Because catheters and grafts are made of plastic and are not normal human tissue, it is very difficult for the white blood cells that fight infection to penetrate into the vascular access material and eradicate the infection. That is why it is often necessary to remove a dialysis catheter or AV graft once it has become infected.

With less serious catheter and graft infections, it is sometimes possible to eradicate the infection with a several-week course of antibiotics. The persistence of fevers, an elevated number of white blood cells in the blood, or constitutional symptoms such as nausea, vomiting, fatigue or persistent pain may be a sign that the antibiotic treatment is unsuccessful and that the access should be removed. If the infection spreads from the catheter or graft into the blood stream, it may travel to other parts of the body producing additional problems in those areas. Staphylococcus is particularly notorious for this complication and may result in infection of the bones (particularly of the spine), heart valves, joints and kidneys.

Hemodialysis catheters are literally infections waiting to happen because they involve a foreign body, a persistent opening through the skin through which bacteria can travel and a patient whose ability to fight infections is impaired. As a result, patients with dialysis catheters are strongly encouraged to have a more permanent vascular access, such as a graft or fistula, placed so that the catheter can be removed and the risk of infection decreased.

AV grafts are less likely to become infected than catheters but, because they are composed of plastic and not natural human tissue, they are more likely to become infected than AV fistulas. This is one of the reasons why AV fistulas are the preferred permanent hemodialysis vascular access. When AV grafts become infected, it is usually because the formation of a hematoma (leakage of blood usually from a needle puncture site under the skin) has become infected and that infection spreads to the graft material nearby. Although an infected hematoma can often be treated effectively with antibiotics, once the infection has spread to the graft material itself, the graft must be removed for the infection to be eradicated.

The spread of infectious agents from the dialysis machine or procedure to the kidney patient is unusual in the setting of current infection control policies but does rarely occur. Even if the dialysate fluid is contaminated with an infectious agent, the dialyzer membrane material is an effective barrier to the spread of that agent from the machine to the patient's blood. Infections related to the dialysis treatment, although unusual, generally occur during the put-on or take-off process when infectious agents can be introduced into the patient's dialysis catheter or permanent vascular access because of improper sterile technique. Therefore, it is important for patients to become familiar with and insist that sterile technique be used during the beginning and ending of dialysis treatment.

Some of the medicines, which patients with certain forms of kidney disease take, may further suppress the immune system and predispose to infection. Patients with kidney diseases related to an inflammatory process such as systemic lupus or vasculitis may be placed on immunosuppressive agents (including prednisone) that can further predispose to infection.

The lymphocytes, which protect against viral and fungal infections, are also involved in rejecting transplanted organs. Therefore, most immunosuppressive agents that are given to patients with organ transplants depress lymphocyte function and increase the patient's susceptibility to viral and fungal infections.

Patients with diabetes, which is the most common cause of kidney failure in the United States , may have additional immune defects as well as vascular disease which may further increase the risk of certain types of infections (particularly fungal infections and infections caused by "anaerobic" organisms that can lead to gangrene). Foot care is particularly important to diabetic patients to diagnose such infections early so that they can be effectively treated with antibiotics.

The best defense against infection is education: understanding the increased risk and recognizing the earliest signs so that infections can be treated effectively. Many dialysis patients do not develop a fever when they are infected, so it is important for them to seek prompt medical attention whenever they develop otherwise unexplained symptoms such as unusual fatigue, loss of appetite, nausea, vomiting and changes in mental activity. Finally, dialysis patients should avoid the prolonged use of hemodialysis catheters because they are associated with frequent and serious infections.

Answer provided by Jay Wish, MD. Dr. Wish is a Professor of Medicine in the Division of Nephrology at University Hospital in Cleveland. He is also a member of the AAKP Medical Advisory Board.

The Dear Doctor column provides readers with an opportunity to submit renal related health questions to healthcare professionals who specialize in the area of concern. The answers are not to be construed as a diagnosis and therefore, altercations in current healthcare should not occur until the patient's physician is consulted.

This article originally appeared in aakpRENALIFE, November 2002 Volume 18 Number 3. 

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