The Estimated Magnitude and Direct Hospital Costs of Prosthetic Joint Infections in the United States, 1997 to 2004 Matthew Hellmann, BA,* Supriya D. Mehta, PhD, MHS, y David M. Bishai, MD, PhD, z Simon C. Mears, MD, PhD, § and Jonathan M. Zenilman, MD* Abstract: To estimate the number and cost of prosthetic joint infection hospitalizations in civilian US hospitals, we analyzed the 1997 to 2004 National Hospital Discharge Survey for the 996.66 International Classification of Diseases discharge code (infection or inflammatory reaction secondary to internal joint prosthesis). The annual number of such hospitalizations averaged 17 589 from 1997 to 2000 and 29 225 from 2001 to 2004. The annual adjusted diagnostic-related group cost for such infection increased from $195 million to $283 million (1997-2004). The mean diagnostic- related group reimbursement ($9034 per hospitalization) did not vary over time or by comorbidity. The nearly doubled number of prosthetic joint infection–related hospitalizations may have been caused by an increased implant rate, changes in patient population, implant procedures, or causative organisms. Keywords: total joint arthroplasty, infection, cost, hospitalization, National Hospital Discharge Survey. © 2010 Elsevier Inc. All rights reserved. Total joint arthroplasty is a highly successful procedure for alleviating the pain and disability of diseases such as rheumatoid arthritis and osteoarthritis [1-4]. The num- ber of patients with prosthetic joints has increased markedly during the past 2 decades [3,5]. In 2004, there were 478 000 primary knee and 234 000 primary hip arthroplasties performed in the United States [6]. Prosthetic joint infection (PJI) is an infrequent but serious complication associated with high morbidity and cost [7-12]. The incidence of PJI has been reported to be 0.5% to 2% [13-24]. Revision procedures have higher infection rates than primary procedures; in some cases, the reason for revision may have been an infection or the infection may not have been identified before revision [13,18,21]. Prosthetic joint infection may occur at any time after joint arthroplasty. Few studies have quantified the national epidemiology of PJIs in terms of economic impact (such as absolute numbers, rate, and cost [8,11,13] in the United States). The National Hospital Discharge Survey (NHDS) is a systematic and statistically validated sample of US hospitalizations that has been collected annually since 1965 from civilian acute care facilities and has national coverage. Because nearly all patients with PJIs are hospitalized, we hypothesized that the NHDS data could provide representative epidemiologic surveillance data on PJI incidence. Our objectives in this study were (1) to estimate the absolute number and rate per person of PJIs in the United States from 1997 to 2004 and to summarize age, race, and sex of patients with PJI hospitalization; (2) to describe the prevalence of comor- bidities among patients with PJI (we hypothesized that a high proportion of PJI occurred in patients with multiple comorbidities); (3) to evaluate whether patient char- acteristics and comorbidities changed over 2 periods, 1997 to 2001 and 2001 to 2004 (these data would assist in generating hypotheses as to whether increased numbers of PJIs may be associated with increased patient risk profile, as defined by older age and comorbidities); and (4) to evaluate diagnosis-related group (DRG) reimbursement and estimate global From the *Division of Infectious Diseases, The Johns Hopkins University School of Medicine, Baltimore, Maryland; yDepartment of Epidemiology and Biostatistics, University of Illinois Chicago School of Public Health, Chicago, Illinois; zDepartment of Population and Family Health Sciences, The Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland; and §Department of Orthopaedic Surgery, The Johns Hopkins University School of Medicine, Baltimore, Maryland. Submitted December 11, 2008; accepted May 24, 2009. The authors thank Cubist Pharmaceuticals, Lexington, Mass, for support through an unrestricted research grant. Reprint requests: Jonathan M. Zenilman, MD, c/o Elaine P. Henze, BJ, ELS, Medical Editor and Director, Editorial Services, Department of Orthopaedic Surgery, Johns Hopkins Bayview Medical Center, 4940 Eastern Ave., #A665, Baltimore, MD 21224-2780. © 2010 Elsevier Inc. All rights reserved. 0883-5403/2505-0015$36.00/0 doi:10.1016/j.arth.2009.05.025 766 The Journal of Arthroplasty Vol. 25 No. 5 2010