818 infection control & hospital epidemiology july 2017, vol. 38, no. 7


orthopedic procedures is approximately $3.5 million,10 and they cost up to 3.8 times more than an uncomplicated proce- dure.11,12 Other estimates have cited $565 million additional costs to hospitals annually due to HACs targeted byCMS, with most of the added cost attributable to orthopedic infections.13 To date, the effect of the CMS nonpayment penalty on patient outcomes has remained unclear. To examine the policy’s impact on targeted orthopedic SSI


rates, we conducted a difference-in-difference analysis com- paring the change in SSI rates among the Medicare population, who were directly affected by the policy before and after October 2008 to the change in rates among a similar age group in the non-Medicare population (control group) from 2000 to 2013. Our study provides new information about the relationship between the CMS nonpayment penalty and the targeted patient safety event.


methods Data


We analyzed data from the Healthcare Cost and Utilization Project (HCUP) National Inpatient Sample (NIS) from 2000 to 2013, the largest publicly available all-payer administrative database on hospital discharges. Following sampling redesign in 2012, the NIS approximates a 20% sample of discharges from all US community hospitals. We selected all inpatient discharges for 60–80-year-old patients who underwent spinal fusions, spinal refusions, and shoulder and elbow arthrodesis and repair procedures. Patients were identified using primary International Classification of Disease, Ninth Revision (ICD-9) procedure and diagnosis codes as defined by CMS.14 (Table 1). Primary payer status was used to differentiate Medicare and non-Medicare patients. In the analyses, we controlled for several patient and hos-


pital characteristics. At the patient level, we controlled for age, gender, race (white, black, Hispanic, Asian, other/missing),


elective admission, and comorbidities present on admission. We also controlled for hospital variables, including median household income for the patient’s ZIP code, teaching hospi- tal, and urban or rural location.


Analysis


Looking at SSI rates during pre- and postpolicy periods, we compared the change in rates of SSI among discharges having Medicare as the primary expected payer (60–80-year-old patients), relative to changes in rates among the non-Medicare population (60–80-year-old patients). The prepolicy period was defined as January 1, 2000, through September 30, 2008, and the postpolicy period was defined as October 1, 2008, through December 31, 2013. The analysis first identified the discharge rates of any diagnosed SSI as defined by the policy (Table 1) among the Medicare and control populations. The rate of SSI was compared pre- and postpolicy implementation among the 2 populations using a difference-in-difference approach,15–17 as in previous studies.18,19 We assumed that both Medicare and non-Medicare populations were similarly affected by larger secular trends and therefore had parallel time trends in SSI rates prior to the intervention. To determine prepolicy parallelism, we tested whether the regression mean functions of the Medicare and control groups were parallel. Because the policy only applied to Medicare patients, the difference in the change in SSI rates after policy implementation between Medicare and non-Medicare populations would be the policy’s intervention effect. Given that SSIs after these procedures were relatively rare events, we estimated rate ratios (RRs) using a Poisson regression model, and we adjusted for other patient- and hospital-level variables. The interaction between time period and payer status (Medicare vs non-Medicare) variables represent the intervention effect. Because not all sampled hospitals had discharges for spinal fusion or shoulder and/or elbow repairs, the use of sampling weights would result in


table 1. Diagnosis and Procedure ICD-9 Codes Identifying Orthopedic Procedures and Surgical Site Infections Type


ICD-9 Code Description


CMS-targeted procedure codes 81.01–81.08 Spinal fusion 81.23–81.24 Arthrodesis of shoulder or elbow 81.31–81.38 Spinal refusion 81.83 81.85


Shoulder repair Elbow repair


Procedures not targeted by CMS 81.80 81.81 81.84 03.09


Diagnosis codes


996.67 998.5


Arthroplasty; other total shoulder replacement Arthroplasty; other partial shoulder replacement Arthroplasty; total elbow replacement


Postoperative infection not elsewhere classified; excludes infections from implanted device, infusion/perfusion or transfusion and postoperative obstetrical wound infections


Infection and inflammatory reaction due to internal orthopedic device, implant or graft Other exploration and decompression of spinal canal NOTE. ICD-9, International Classification of Disease, Ninth Revision; CMS, Centers for Medicare and Medicaid Services.


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