Analysis of the Impact of Surgical Site Infections on Post-Operative Length of Stay Following Hip Replacements and Revisions in New York State, 2008–2012

BACKGROUND: Each year in the United States, an estimated 332,000 hip replacement procedures are performed. Surgical site infection (SSI) can result in reduced quality of life and decreased functional outcomes. In New York State (NYS), acute care hospitals are required to track and report SSIs following hip surgery via the Centers for Disease Control and Prevention’s National Healthcare Safety Network (NHSN). NHSN classifies SSIs as superficial incisional primary (SIP), deep incisional primary (DIP), and organ/space (OS). This analysis explores the relationship between SSI infection depth and post-operative length of stay (LOS). 

METHODS: A retrospective study design of patients greater than 18 years of age who underwent a hip replacement or revision in NYS from 2008–2012 was performed. Procedure specific data from NHSN were paired with data from the Statewide Planning and Research Cooperative System (SPARCS) to obtain information on LOS and readmission. The primary outcome was post-operative LOS, defined as the sum of the number of days hospitalized following hip surgery and the total number of days of the first readmission to any hospital within one year for any reason. Multivariate linear regression models controlling for patient characteristics were used to estimate the mean LOS associated with SSI infection depth. To explore the relationship between SSI infection depth and pathogen distribution, descriptive statistics were calculated. 

RESULTS: From 2008–2012, a total of 132,192 hip replacements and revisions were performed in NYS; 6% (n=7,983) were excluded from analysis due to age, post-operative death, or incomplete data. Of the remaining 124,209 surgeries, 1% (n=1,437) resulted in SSI (SIP: 30% (n=438), DIP: 43% (n=614), OS: 27% (n=385)). Compared to patients without SSIs, patients with SSIs experienced a longer total LOS: SIP (+1.85 days, 95% CI: 1.76–1.95), DIP (+1.81 days, 95% CI: 1.73–1.89), or OS (+1.67 days, 95% CI: 1.58–1.76). Eighty-five percent (n=1,233) of all SSIs were detected on readmission, while 8% (n=109) were detected on current admission and 7% (n=95) on post-discharge surveillance. For all SSI depths, the three most common infectious etiologies were Staphylococcus aureus (54%, n=780), coagulase-negative staphylococci (14%, n=201), and enterococci (11%, n=153). 

CONCLUSIONS: In NYS, patients with SSIs following hip replacement or revision had a significantly longer LOS compared to patients without SSIs. SIP SSIs resulted in a similar increase in post-operative LOS as DIP and OS SSIs. Moreover, across SSI depths, the infectious etiologies remained the same.