Clinical Outcomes and Costs Due to Staphylococcus

Clinical Outcomes and Costs Due to Staphylococcus aureus Bacteremia Among Patients Receiving Long‐Term Hemodialysis • Author(s): John J. Engemann , MD; Joëlle Y. Friedman , MPA; Shelby D. Reed , PhD; Robert I. Griffiths , MS, ScD; Lynda A. Szczech , MD, MSCE; Keith S. Kaye , MD, MPH; Martin E. Stryjewski , MD; L. Barth Reller , MD; Kevin A. Schulman , MD; G. Ralph Corey , MD; Vance G. Fowler , Jr., MD, MHS Source: Infection Control and Hospital Epidemiology, Vol. 26, No. 6 (June 2005), pp. 534-539 Published by: The University of Chicago Press on behalf of The Society for Healthcare Epidemiology of America Stable URL: http://www.jstor.org/stable/10.1086/502580 . Accessed: 22/11/2013 11:12 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp

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534

INFECTION CONTROL AND HOSPITAL EPIDEMIOLOGY

June 2005

CLINICAL OUTCOMES AND COSTS DUE TO STAPHYLOCOCCUS AUREUS BACTEREMIA AMONG PATIENTS RECEIVING LONG-TERM HEMODIALYSIS John J. Engemann, MD; Joëlle Y. Friedman, MPA; Shelby D. Reed, PhD; Robert I. Griffiths, MS, ScD; Lynda A. Szczech, MD, MSCE; Keith S. Kaye, MD, MPH; Martin E. Stryjewski, MD; L. Barth Reller, MD; Kevin A. Schulman, MD; G. Ralph Corey, MD; Vance G. Fowler, Jr., MD, MHS

ABSTRACT

OBJECTIVE: To examine the clinical outcomes and costs associated with Staphylococcus aureus bacteremia among hemodialysis-dependent patients. DESIGN: Prospectively identified cohort study. SETTING: A tertiar y-care university medical center in North Carolina. PATIENTS: Two hundred ten hemodialysis-dependent adults with end-stage renal disease hospitalized with S. aureus bacteremia. RESULTS: The majority of the patients (117; 55.7%) under went dialysis via tunneled catheters, and 29.5% (62) under went dialysis via synthetic arteriovenous fistulas. Vascular

access was the suspected source of bacteremia in 185 patients (88.1%). Complications occurred in 31.0% (65), and the overall 12-week mortality rate was 19.0% (40). The mean cost of treating S. aureus bacteremia, including readmissions and outpatient costs, was $24,034 per episode. The mean initial hospitalization cost was significantly greater for patients with complicated versus uncomplicated S. aureus bacteremia ($32,462 vs $17,011; P = .002). CONCLUSION: Inter ventions to decrease the rate of S. aureus bacteremia are needed in this high-risk, hemodialysisdependent population (Infect Control Hosp Epidemiol 2005;26:534539).

Staphylococcus aureus is a serious, common cause of bacteremia. S. aureus is one of the most common pathogens isolated from the bloodstream,1 and rates of S. aureus bacteremia are increasing.2-4 During the 1980s, the rate of nosocomial primary bloodstream infection due to S. aureus more than doubled in hospitals reporting to the National Nosocomial Infections Surveillance System.4 Infectious complications of S. aureus bacteremia, such as endocarditis, osteomyelitis, and metastatic abscesses, are also common and may be increasing in frequency.5-7 Patients undergoing hemodialysis are at particularly high risk of developing S. aureus bacteremia.8-11 The annual incidence of S. aureus bacteremia among hemodialysis-dependent patients is 3% to 4%.11 The incidence of S. aureus bacteremia among patients with tunneled, cuffed hemodialysis catheters ranges from 0.6 to 3.9 per 1,000 catheter-days.10,12,13 In addition, hemodialysis-dependent patients with S. aureus bacteremia are at high risk for complications14 and recurrent infections.15,16 Despite its clinical significance, the economic impact of S. aureus bacteremia is poorly understood. Prior investiga-

tions17,18 have provided important insights into the economic burden of S. aureus. However, these studies had several limitations, including small sample size,17 retrospective design,18 a wide range of acute and underlying comorbid conditions,17,18 economic models combining cost estimates from multiple sources,18 and use of charges,18 which are not representative of true economic costs. No studies to date have rigorously quantified the cost of S. aureus bacteremia in a large cohort of prospectively identified patients with the same underlying comorbid conditions. We sought to describe the clinical outcomes, use of associated healthcare resources, and infectionassociated costs of S. aureus bacteremia in a large cohort of prospectively identified, hemodialysis-dependent patients with S. aureus bacteremia. METHODS Subjects and Setting All adult patients who were undergoing hemodialysis for chronic renal failure and who were admitted to Duke University Hospital with S. aureus bacteremia between

Drs. Engemann, Kaye, Stryjewski, Reller, Corey, and Fowler are from the Division of Infectious Diseases, Department of Medicine; Dr. Szczech is from the Division of Nephrology, Department of Medicine; Dr. Reller is also from the Clinical Microbiology Laboratory, Department of Pathology; Ms. Friedman and Drs. Reed and Schulman are from the Center for Clinical and Genetic Economics; and Ms. Friedman and Drs. Reed, Schulman, Szczech, Stryjewski, Corey, and Fowler are also from the Duke Clinical Research Institute, Duke University Medical Center, Durham, North Carolina. Dr. Griffiths is from Health Economics Consulting, Annapolis, Maryland. Address reprint requests to John J. Engemann, MD, Box 3038, Duke University Medical Center, Durham, NC 27710. [email protected] Supported in part by a research agreement between Duke University and Nabi Biopharmaceuticals. Dr. Engemann was supported by a fellowship from the Agency for Healthcare Research and Quality. Dr. Fowler was supported by grant AI-01647 from the National Institutes of Health. The authors thank Pamela R. Brown, RN; Lynn S. Harrington, RN, BSN; Annette B. McDaniel, MEd, MA; and Debra A. Montgomery, RN, MSN, for assistance with collection and preparation of the data for analysis. They also thank Damon M. Seils, MA, for editorial assistance and manuscript preparation. Presented in part at the 43rd Interscience Conference on Antimicrobial Agents and Chemotherapy; September 14-17, 2003; Chicago, IL.


Vol. 26 No. 6

S. AUREUS BACTEREMIA AMONG HEMODIALYSIS PATIENTS

September 1, 1994, and August 31, 2001, were identified prospectively and included in the study. Clinical characteristics of a subset of the patients in this study have been described previously.14 Daily reports were received from the microbiology laboratory regarding all patients with one or more blood cultures positive for S. aureus. All patients were evaluated within 36 hours of identification of S. aureus. Exclusion criteria included S. aureus bacteremia in non-hospitalized patients, age younger than 18 years, polymicrobial infection, neutropenia (absolute neutrophil count, < 1.0  109/L), and death prior to evaluation by the investigators. Patients who were not undergoing hemodialysis at the time of admission were also excluded from the study. The institutional review board of Duke University Medical Center approved this study. Data Collection Clinical data were collected at the time of patient hospitalization by investigators and were entered into an electronic database (Access, Microsoft Corp., Redmond, WA). Acute Physiology and Chronic Health Evaluation II scores were calculated on the date of initial positive blood culture.19 To preserve the statistical assumption of independence of observations, only the initial episode of bacteremia for each patient was included in the study. Clinical outcomes were assessed 12 weeks after the date of the initial positive blood culture. Supplemental data regarding diagnostic and therapeutic studies were obtained via medical record abstraction. An episode of bacteremia was defined as healthcare associated if positive blood cultures were performed within 72 hours of admission and nosocomial if they were performed more than 72 hours after admission. Corticosteroid use was defined as either chronic low-dose or acute highdose therapy.19 The source of bacteremia was considered to be a tissue infection if local signs of infection occurred prior to the diagnosis of bacteremia. An intravascular catheter was considered to be the portal of entry if inflammation was present around the insertion site, a catheter tip culture was positive for S. aureus, or both and no other source was evident.20 Septic shock was defined by standard criteria.21 Patients with complicated infection had a site of infection remote from the primary focus caused by hematogenous seeding (eg, endocarditis or vertebral osteomyelitis) or extension of infection beyond the primary focus (eg, septic thrombophlebitis or abscess). All cases of complicated infection were defined independently by radiologic imaging, culture of S. aureus from a normally sterile site, or the use of validated diagnostic criteria.22 Infective endocarditis was defined according to Duke criteria.23 Septic arthritis was defined by a positive result on Gram staining or isolation of S. aureus from synovial fluid or other tissues isolated from a joint space in the presence of bacteremia. Osteomyelitis was defined as the isolation of S. aureus from bone or intervertebral disk space or by radiographic evidence of osteomyelitis in the presence of S. aureus bacteremia.5 Deaths were attributed to S. aureus infection if there was clinical and microbiologic evidence of infection at the time of death without an alternative explanation.

535

Cost Data Cost analysis proceeded from the perspective of the healthcare system. Complete billing information (which included costs and charges) from the hospital accounting system (Transition Systems, Inc., Boca Raton, FL) was available for all patients hospitalized after July 1, 1996. Patients were included in the study only if their initial admission was due to S. aureus bacteremia. The entire cost of that admission was attributed to the infection. Outpatient costs and rehospitalization costs were included only for procedures and admissions related to S. aureus infection during the 12 weeks following the initial positive blood culture (eg, if a patient subsequently underwent debridement of an abscess or replacement of a vascular access device that was removed due to infection). Hospital costs and charges were obtained from the hospital accounting system and were adjusted to 2001 U.S. dollars using the Consumer Price Index for Medical Care.24 Charges were reported to allow direct comparisons with published estimates from prior studies. Results were reported as means, the preferred measure for reporting in economic analyses.25 Physicians’ fees were assigned to procedures performed to diagnose or treat a condition resulting from S. aureus infection and to care provided during the initial hospitalization, readmissions, and outpatient visits. Physicians’ fees were based on 2001 reimbursement rates from the Centers for Medicare & Medicaid Services for providers in North Carolina. Statistical Analyses Descriptive statistics are presented as counts and percentages for discrete variables. Continuous variables are reported as means and standard deviations. Means, standard deviations, and medians are reported for cost data. Continuous clinical variables were compared using the Student’s t test. Tests were two-tailed, with a P value of .05 or less considered statistically significant. Cost comparisons between patients with and without complications were performed using a generalized linear regression model specified using a log link and the gamma family of distributions to account for heteroskedasticity associated with the cost data.26 RESULTS From September 1994 through August 2001, a total of 210 patients with end-stage renal disease who were undergoing chronic hemodialysis were treated at Duke University Hospital for S. aureus bacteremia. Patient characteristics are listed in Table 1. The mean age of patients was 54.7 years; 114 patients (54.3%) were women, and 165 (78.6%) were African American. The most common causes of renal failure were hypertension (54.8%) and diabetes mellitus (46.2%). The mean duration of hemodialysis among study subjects was 2.9 years. The most common types of hemodialysis access were tunneled, cuffed dual lumen catheters (117; 55.7%) and polytetrafluoroethylene grafts (62; 29.5%). Although 18.6% of the patients had primary arteriovenous fistulas present at the time of admission, most were not actively being used—only 2 patients (1.0%)



536

TABLE 1 PATIENT CHARACTERISTICS (N = 210) Characteristic

No.

Mean age, y (± SD)

TABLE 2 COMPLICATIONS AND OUTCOMES OF STAPHYLOCOCCUS AUREUS BACTEREMIA (N = 210) No. (%) of Patients

54.7 (± 15.1)

Male

96 (45.7%)

Race African American

165 (78.6%)

White

42 (20.0%)

Other

3 (1.4%)

Comorbidities Diabetes mellitus*

109 (51.9%)

Injection drug use

19 (9.1%)

Immunosuppression due to corticosteroid use

18 (8.6%)

Malignancy

8 (3.8%)

HIV infection

5 (2.4%)

History of infective endocarditis

5 (2.4%)

Characteristics of kidney disease Presumed etiology of kidney failure Diabetes mellitus

97 (46.2%)

Hypertension

115 (54.8%)

Glomerulonephritis

14 (6.7%)

Other or unknown

39 (18.6%)

History of kidney transplantation†

27 (12.9%)

Mean duration of hemodialysis, y (± SD)

2.9 (± 3.6)

Hemodialysis access (in use at admission) Tunneled, cuffed catheter

117 (55.7%)

Polytetrafluoroethylene graft‡

62 (29.5%)

Primary arteriovenous fistula§

2 (1.0%)

Temporary catheter

3 (1.4%)

Implanted subcutaneous access device Unknown

1 (0.5%) 25 (11.9%)

Signs and symptoms at admission Temperature > 38°C

200 (95.2%)

Evidence of central nervous system involvement

32 (15.2%)

Heart failure

18 (8.6%)

Septic shock (systolic blood pressure < 90 mm Hg)

31 (14.8%)

Presumed source of bacteremia Hemodialysis access

185 (88.1%)

Tissue source

4 (1.9%)

Device other than hemodialysis access

2 (1.0%)

Other

5 (2.4%)

Unknown

14 (6.7%)

Nosocomial acquisition

14 (6.7%)

MRSA infection

70 (33.3%)

SD = standard deviation; HIV = human immunodeficiency virus; MRSA = methicillin-resistant Staphylococcus aureus. *Includes 61 patients with insulin-dependent diabetes mellitus. † All patients were undergoing hemodialysis at the time of admission. ‡ Polytetrafluoroethylene grafts (including nonfunctional) were present in 109 (51.9%) of the patients. § Primary arteriovenous fistulas (including nonfunctional) were present in 39 (18.6%) of the patients.

admitted with bacteremia had undergone dialysis via native vessel fistulas. The vascular access device was the suspected source of bacteremia in 185 patients (88.1%). Other prosthetic devices were present in 6 patients: 4

June 2005

Complication Any complication*

65 (31.0)

Infective endocarditis

36 (17.1)

Osteomyelitis

12 (5.7)

Abscess

12 (5.7)

Septic arthritis

10 (4.8)

Septic emboli

10 (4.8)

Meningitis

5 (2.4)

Stroke

3 (1.4)

Septic thrombophlebitis

3 (1.4)

Other†

11 (5.2)

Outcome Mortality at 12 wk‡

40 (19.0)

Due to S. aureus

22 (10.5)

Due to other causes Recurrent S. aureus infection at 12 wk

18 (8.6) 27 (12.9)

*Although individual patients may have had more than one complication, they were counted only once in the “any complication” category. † Other complications included mycotic aneurysm, pericarditis, pneumonia, and pseudoaneurysm. ‡ In-hospital mortality was as follows: overall, 20 (9.5%); due to S. aureus, 15 (7.1%); and due to other causes, 5 (2.4%).

pacemakers or defibrillators, 1 heart valve, and 1 orthopedic device. S. aureus infection was suspected at admission in only 76.2% (160) of the patients. Twenty-four percent of the patients were initially believed to have other medical issues necessitating admission. One-third (70) of the study patients had methicillin-resistant S. aureus bacteremia. More than 70% (151) of the patients received vancomycin as the principal antibiotic therapy. The mean duration of antimicrobial therapy was 28.3 days (standard deviation, ± 17.4 days; range, 5 to 184 days). Thir ty-one percent of the patients developed a complication of S. aureus bacteremia (Table 2). Endocarditis was present in 17.1% of the patients, abscess in 5.7%, septic ar thritis or septic emboli in 4.8%, and meningitis in 2.4%. Twelve patients had osteomyelitis, primarily consisting of ver tebral infection (8; 67%). At the time of discharge from the hospital, 81% of the patients were thought to be cured of infection. Twenty-seven patients (12.9%) developed recurrent infection due to S. aureus within 12 weeks. Twenty patients (9.5%) died during the initial hospital admission; 20 additional patients died in the 3 months after diagnosis of S. aureus bacteremia. The overall mor tality rate at 12 weeks was 19%. Diagnostic and Therapeutic Procedures Radiologic and surgical procedures used to diagnose the extent of and guide the treatment of complications of S. aureus bacteremia are detailed in Table 3. Echocardiog-


Vol. 26 No. 6


raphy was performed in 68% of the patients; two-thirds of these studies were transthoracic. The bulk of surgical procedures performed were device related; 80.5% (169) of the patients underwent at least one such procedure, most related to removal or replacement of vascular access. Three patients had infected pacemakers or defibrillators removed. One patient with prosthetic valve endocarditis underwent valve replacement, and another patient had an infected hip prosthesis removed. Fourteen percent (30) of the patients underwent at least one surgical procedure unrelated to an implanted device. Duration of Hospitalization During the index admission, patients were hospitalized for a median of 9 days (mean, 14.7 days; interquartile range, 6 to 16 days) due to S. aureus infection. When the days prior to the blood culture positive for S. aureus were excluded, the median length of stay was 8.5 days (mean, 13.3 days). Forty-eight patients (22.9%) were hospitalized in the intensive care unit. The bulk of patient hospital days were spent on general wards (median, 8 days; interquartile range, 5 to 13 days). Forty-three patients (20.5%) were readmitted within 12 weeks for reasons related to the initial S. aureus infection. The median length of hospitalization for readmissions was 7 days (mean, 10.7 days). Readmissions were due to recurrent bacteremia in 33 patients (69% of readmissions and 15.8% of the overall cohort) and revision of vascular access in 10 patients (23% of readmissions and 4.8% of the overall cohort). Fifty-four patients (25.7%) had a total of 97 outpatient visits attributable to S. aureus infection. Eighty-three (85.6%) of these outpatient visits were to specialists; the remainder were to the emergency department. Costs Cost data were available for all patients admitted after July 1, 1996 (143; 68.1%). The mean cost of the initial hospitalization was $20,685 per patient (median, $15,121), with physicians’ fees making up $1,941 (median, $1,588) of the total (Table 4). Twenty (14%) of the 143 patients for whom cost data were available were rehospitalized for reasons associated with the index S. aureus infection. The mean cost of each readmission was $24,317. Twenty-five percent of these 143 patients with cost data had outpatient services related to S. aureus. Among these patients, the mean outpatient cost was $330 per patient. Hospitalization costs for patients with arteriovenous fistulas (mean, $17,888; median, $13,792) and for patients with tunneled, cuffed catheters (mean, $22,430; median, $15,155) did not differ significantly (P = .20). The mean total cost of the initial hospitalization was significantly higher among patients with complicated S. aureus bacteremia ($32,462 ± $25,281; median, $25,762) versus uncomplicated S. aureus bacteremia ($17,011 ± $16,889; median, $12,853; P = .002). On average, patients with endocarditis were 1.73fold more costly (95% confidence interval [CI95], 1.27 to 2.35) and patients with septic arthritis were 1.81-fold more costly (CI95, 1.08 to 3.02) than patients with uncomplicated bacteremia. Patients with osteomyelitis were, on average,

537

TABLE 3 DIAGNOSTIC AND THERAPEUTIC PROCEDURES (N = 210) Procedure

No. (%) of Patients

Diagnostic study* Echocardiography

143 (68.1)

Transthoracic

135 (64.3)

Transesophageal

75 (35.7)

Computed tomography scan

67 (31.9)

Magnetic resonance imaging

31 (14.8)

Ultrasound

64 (30.5)

Nuclear medicine

26 (12.4)

Other non-interventional diagnostic tests

25 (11.9)

Interventional diagnostic tests†

95 (45.2)

Lumbar puncture

12 (5.7)

Surgical procedures related to hemodialysis access‡ Tunneled, cuffed catheter§

123

Removal

119 (96.7)

Replacement

100 (81.3)

Temporary catheter

210

Removal

109 (51.9)

Replacement

108 (51.4)

Polytetrafluoroethylene graft§

109

Removal

35 (32.1)

Debridement or drainage

18 (16.5)

Replacement

12 (11.0)

Thrombectomy

11 (10.1)

Primary arteriovenous fistula§

39

Removal

2 (5.1)

Debridement or drainage

3 (7.7)

Replacement

2 (5.1)

Thrombectomy

3 (7.7)

Surgical procedures on native tissues Debridement or replacement of heart valve

2 (1.0)

Debridement or drainage of joint

4 (1.9)

Debridement or drainage of spine

6 (2.9)

*Performed during the initial admission and the 12-week follow-up period. Patients with more than one identical procedure were counted only once for that procedure. Percentage of patients reflects the percentage of the cohort of 210 who underwent the procedure. † Includes aspiration or biopsy. ‡ Percentage of patients with an access device who underwent the procedure. § Performed during the initial admission and the 12-week follow-up period. Subcategories are not mutually exclusive.

1.38-fold more costly, but this finding was not statistically significant (CI95, 0.87 to 2.19). The mean total charge for the initial admission was $31,964 (standard deviation, ± $33,742; median, $21,672). For the 19 patients with available financial data who were readmitted, the mean rehospitalization charge was $31,620 (standard deviation, ± $25,172; median, $25,520). The mean total charge, exclusive of charges for outpatient care, for an episode of S. aureus bacteremia was $36,165 (standard deviation, ± $35,797; median, $25,724).


538


June 2005

TABLE 4 HOSPITAL COSTS (N = 143)* Item

Mean (SD)

Median (IQR)

18,744 (18,874)

13,339 (8,059–22,730)

Initial hospitalization (n = 143) Medical care Physicians’ fees Subtotal

1,941 (1,717)

1,588 (915–2,450)

20,685 (20,225)

15,121 (8,892–24,612)

23,419 (17,563)

19,556 (10,553–35,414)

Rehospitalization (n = 19)† Medical care Physicians’ fees

898 (568)

689 (526–1,180)

24,317 (17,988)

19,973 (11,093–36,866)

468

257

Initial hospitalization

20,685 (20,225)

15,121 (8,892–24,612)

Rehospitalization‡

3,230 (10,470)

0

Subtotal Outpatient care (n = 36)† Total costs

Outpatient care‡ Total

118

0

24,033 (21,995)

17,187 (10,665–29,425)

SD = standard deviation; IQR = interquartile range. *Costs are reported in 2001 U.S. dollars for all patients admitted after July 1996. † Includes patients who were initially admitted after July 1996. Cost data for the patients who were readmitted (n = 19) and the patients who incurred costs for outpatient care (n = 36). ‡ Reflects costs averaged for 143 patients.

DISCUSSION S. aureus is an increasing cause of morbidity, mortality, and expense. Accurately quantifying the full impact of this pathogen on patients and on the healthcare system has been limited by the absence of data from a large cohort of well-characterized patients with a common acute (bacteremia) and chronic (hemodialysis) condition. Previous studies focused on the epidemiology of S. aureus bacteremia and associated clinical outcomes in a population with end-stage renal disease,8-16 but did not enumerate the considerable diagnostic and therapeutic resources required to diagnose and treat S. aureus bacteremia and its complications. Published studies regarding the economic burden of S. aureus bacteremia have not provided detailed information regarding the clinical outcomes and complications of infection.17,18 In addition, prior studies of S. aureus used charge estimates, whereas cost data better represent the true value of resources consumed and are the preferred metric when reporting the economic burden of a condition.27 Our analysis employed detailed information on resource use and economic costs from the largest prospectively identified cohort of hemodialysis-dependent patients with S. aureus bacteremia reported to date. The results of our study yielded several key findings. First, the mean cost of S. aureus bacteremia in this population of hemodialysis-dependent patients was considerable ($24,034 per patient). These results are consistent with those of prior studies17,18 but represent a novel contribution because the current study reflects cost data, was not restricted to patients with nosocomial infection, and included directly measured cost data rather than estimates obtained via modeling. Prior studies of S. aureus found the direct medical charges attributable to S. aureus bacteremia to total $31,300 per case18 and the cost of an episode of

bacteremia to range from $9,661 to $27,083.17 The former study modeled charges using administrative data, and the latter study was restricted to nosocomial infections. Second, resource use associated with S. aureus bacteremia in dialysis patients was substantial. Two-thirds of the patients underwent echocardiography; almost half of the patients in this study underwent invasive diagnostic procedures related to their infection, such as biopsy or aspiration. Vascular access was the presumed source of bacteremia in 89% of the patients; this necessitated the removal of catheters in 97% of the patients with tunneled, cuffed catheters and the removal of grafts in 32% of the patients with synthetic grafts. Given the limited options for vascular access in many patients receiving chronic hemodialysis, loss of vascular access represents a devastating consequence of this infection. Finally, the use of vancomycin in this study population was much greater than would have been expected based solely on the rate of infection due to methicillin-resistant S. aureus. The overall complication rate in this cohort was consistent with the rates of prior studies and highlighted the high risk of metastatic complications among patients with S. aureus bacteremia. Transesophageal echocardiography has been recommended by some authorities to rule out vegetations in patients with catheter-associated bloodstream infections due to S. aureus.28 Given the frequency of endocarditis among the patients in this study (17%), strong consideration should be given to the use of transesophageal echocardiography in hemodialysis patients with S. aureus bacteremia. Complications significantly increase the cost associated with treating S. aureus infections: the mean cost was $14,000 more for patients with complicated S. aureus bacteremia compared with patients with uncomplicated


Vol. 26 No. 6


bacteremia. Given the high risk for complications and increased costs, potential interventions to decrease rates of infection, such as vaccination29 or nasal decolonization,30 may be particularly important in hemodialysis patients. There are several limitations to this study. First, we did not capture costs for patients admitted to outside hospitals. However, follow-up at 12 weeks was performed for all patients, so the risk of missing an admission to an outside hospital was small. Second, the cost analysis was restricted to patients admitted to the hospital for treatment of bacteremia, as we did not include individuals who were treated solely as outpatients. However, because most patients with S. aureus bacteremia are treated as inpatients, this fact is unlikely to have significantly affected our results. Third, referral bias could have overestimated the true cost of bacteremia if patients with uncomplicated bacteremia were preferentially admitted to other hospitals. This risk was minimized because the majority of the patients in this study were from Duke University Health System–affiliated hemodialysis units for which our institution is the primary healthcare facility. Finally, we did not have access to cost data for patients hospitalized prior to July 1996. However, the reported cost data were obtained from a robust sample (n = 143) representing recent treatment patterns and may be more generalizable to current clinical practice. The findings from this study highlight that 3 of every 10 patients undergoing hemodialysis who develop S. aureus bacteremia will suffer a complication. In addition to the substantial morbidity and mortality associated with S. aureus infection, the economic cost of S. aureus bacteremia in this population is striking. The total cost of treating the 143 patients admitted to the hospital after July 1996 was $3.45 million. The number of patients with end-stage renal disease receiving chronic hemodialysis in the United States was 246,000 in 2000 and is projected to increase by an average of 7.1% annually through 2009.31,32 Effective interventions to prevent S. aureus bacteremia in this growing, highrisk population are needed. REFERENCES

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