Pharmacology
The attributable clinical and economic burden of skin and skin structure infections in hospitalized patients: a matched cohort study

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Abstract

We estimated the incremental clinical and economic burden of skin and skin structure infections (SSSI) in hospitalized patients using a matched cohort study design. Cases with SSSI as secondary diagnosis were matched with up to 4 randomly selected non-SSSI controls by age, gender, admission date, and ICD-9 code of principal diagnosis. Among the 1 472 965 hospitalizations episodes, 23 026 had SSSI as their secondary diagnosis. Matching was successful in 22 551 (98%) cases. Compared with controls (n = 87 811), the cases had an average mean unadjusted length of hospital stay (LOS) of 5 days longer and excess hospital charges over $21 000 and higher mortality rate (5.4% versus 3.5%). Adjusted estimates from regression models revealed that SSSI incurred on average 3.81 additional days and $14 794 excess hospitalization charges. Risk of mortality was significantly higher in the cases (odds ratio, 1.32). P value was <0.0001 for all unadjusted and adjusted outcomes. Compared with their matched controls, patients with SSSI had significantly longer LOS, higher mortality, and higher hospital charges.

Introduction

Complicated skin and skin structure infections (SSSIs) represent different types of infections with varying degrees of severity, including surgical site infections (SSIs), diabetic foot infections (DFIs), cellulitis, osteomyelitis, necrotizing fasciitis, and burn infections (Lee et al., 2005). Estimates from the Medicare beneficiary data found that there were more than 330 000 cellulitis-related and 16 000 osteomyelitis-related hospitalizations in the United States in 1995 (Eron et al., 2003). Recently, McCaig et al. (2006) from the Centers for Diseases Control estimated that there were 11.6 million SSSI-related emergency room and outpatients clinic visits in the United States for the years 2001 to 2003. This figure represented 1% of all ambulatory visits made, with a standardized visit rate of 410.7 per 10 000 persons. Authors further noted that although the overall rate of visits during the years 2001 to 2003 was not different than that encountered for the years 1992 to 1994, the proportions of SSSI cases seen in outpatient clinics and emergency rooms increased by 59% and 31%, respectively. Furthermore, 4% of SSSI cases seen in ambulatory care settings ended up in hospitalizations.

Because SSSI are caused primarily by Gram-positive pathogens, with Staphylococcus aureus as the predominant pathogen (Lee et al., 2005), their clinical management is further complicated by the increasing prevalence of multidrug-resistant pathogen isolates that were associated with these infections, including methicillin-resistant S. aureus (Frazee et al., 2005, Moet et al., 2007). Aside from the clinical challenges associated with the management of patients, SSSI leads to increase in the cost of hospitalizations (Davis et al., 2007, Shorr, 2007). In this regard, a recent noteworthy ruling was announced by Centers for Medicare and Medicaid Services (CMS), the agency responsible among other things, for the financial managements of both Medicare and Medicaid. As part of the Deficit Reduction Act of 2005, the Secretary of Health and Human Services was requested to identify conditions that are as follows: a) high cost or high volume or both, b) result in the assignment of a case to a Diagnosis-related Group (DRG) that has a higher payment when present as a secondary diagnosis, and c) could reasonably have been prevented through the application of evidence-based guidelines. As a result, CMS announced it will no longer pay for the costs of services incurred in the management of certain surgical site skin type infections occurring during hospitalizations, after October 1, 2008, if these infections were not present on admission (Medicare Program, 2007). Such ruling will most likely increase the economic burden on payers and calls for better management of SSSI during hospitalization. The overall objective of this study was to estimate the incremental clinical and economic burden attributable to SSSI as measured by excess length of hospital stay (LOS), total hospital charges, and mortality.

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Materials and methods

Because of the difficulty in separating the incremental outcomes of SSSI from those related to the underlying diseases, a matched cohort design was employed. The study was designed to estimate the incremental outcomes due to SSSI by comparing 2 groups of patients sharing similar principal diagnoses and differing in whether they had SSSI or not. By controlling for principal diagnoses, differences in outcomes between the 2 groups are most likely attributable to whether patients had SSSI as

Results

Among the 1 472 965 hospitalizations included in the database, 47 889 SSSI cases were extracted. After excluding 128 cases with appendicitis, 752 cases with peritonitis, and 3808 cases with pneumonia, 43 201 cases (or 2.93% of 1 472 965) with SSSI as principal (20 175 cases or 47% of 43 201) or secondary diagnosis (23 026 cases or 53%) remained. The group with principal SSSI included 47 DFI cases (0.2% of 20 175), 11 099 cellulitis cases (55.0%), 8256 SSI cases (40.9%), 512 cases of

Discussion

On all outcome parameters measured, patients with SSSI did not fare as well as their matched controls. Cases had higher CCI score (i.e., with more comorbidities and/or more severe comorbidities), were less likely to be home discharged, and were almost twice as likely to be discharged to skilled nursing home facility. Also, cases had higher intensity of services and consequently incurred higher overall hospital charges. The conservative adjusted estimate on excess LOS is 3.2 days in mean and 2

Acknowledgments

This study was supported by a contract from Johnson and Johnson Pharmaceutical Services, LLC, Raritan, NJ, to Hind T. Hatoum and Company, Chicago, IL.

K.A. Akhras is an employee of Johnson and Johnson. Both H.T. Hatoum and S.J. Lin are paid consultants to Johnson and Johnson Pharmaceutical Services, LLC.

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Partial data were presented at Society for Healthcare Epidemiology of America (SHEA) Annual Meeting, Orlando, FL, April 2008.

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