Infection Control & Hospital Epidemiology Revision procedures
Revisions are an infrequent outcome of a primary arthroplasty and can occur at any time following the initial arthroplasty.22 We created a cohort of individuals eligible for a revision who had previously had a primary procedure. This cohort was estimated from 2000 through 2014 using the NIS data and data obtained from our primary arthroplasty model from 2015 onward. Revision rates were based on published literature sources esti-
mating the risk of revision following primary arthroplasties. Sources showed similar rates of revision for hip and knee arthroplasties (ranging from 81.2% to 96% implant survival at 10 years).22–26 For this study, we applied rates from Katz et al22 to all age and gender cohorts for all arthroplasties. We selected the data from Katz et al because their rates were calculated using a large administrative dataset (vs a single facility) over a 12-year time period. Revision SSI rates were estimated from NHSN data following
revision hip and knee arthroplasty for years 2012 through 2015 stratified by age and gender.Weutilized SSI counts standardized by NHSN arthroplasty totals, averaged across years 2012 through 2015, and input them into the model as time-constant infection rates.
Mortality rate
Background mortality was obtained from the US Census Bureau estimates and projections for 2000 through 2030 stratified by age (until age 85, where the mortality rate applied to age 85 and over). The model applied the mortality rate to individuals in the simulated baseline population who had not already received an arthroplasty (primary or revision dependent on model) based on the current year and current age of the individual.
HHS action plan goals
To assess the potential impact the HHS target rate reduction would have on SSI burden from 2020 to 2030, we reduced each stratified rate in our model by 30% beginning in 2020 and sus- tained through 2030. We compared these results with the original projections.
Obesity rate
To assess the model’s sensitivity to changes in comorbidities, we conducted a secondary analysis utilizing projected obesity
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increases and stratified obesity rates. Finkelstein et al27 projected that obesity (defined as BMI ≥ 30) would increase from 34% in 2015 to 42% in 2030. Using these projections, we stratified the baseline population into nonobese and obese. We obtained stra- tified relative risks for obese and nonobese populations for pri- mary arthroplasties using 2012–2014 Cerner HealthFacts, a large electronic health records database. We estimated BMI-stratified SSI rates from 2012–2015 NHSN data. We applied these relative risks as multipliers to our previous primary arthroplasty and SSI rates to calculate the estimated obese and nonobese arthroplasty and SSI rates. Thus, we obtained a baseline population rate, an arthroplasty rate, and an SSI rate for each gender, age, and BMI cohort (Appendix Table 1). We ran the primary model with the new cohorts with and without increasing population obesity rates from 2015 through 2030.
Results
Our model projected 15,820,475 primary and revision hip and knee arthroplasties and 77,653 subsequent SSIs from 2020 through 2030. The number of arthroplasties increased 13%, with a 14% increase in total SSIs, representing 179,106 additional arthroplasties and 937 additional SSIs in 2030 compared to 2020 (Fig. 2 and Appendix Table 2). Primary and revision hip arthroplasties combined were pro-
jected to increase by 15%, and subsequent SSIs increased by 16% to 4,063 infections in 2030 (Fig. 2 and Appendix Table 2). The model projected primary and revision knee arthroplasties would increase by 12%, and subsequent SSIs following knee arthro- plasties would increase by 13%, with 3,443 SSIs in 2030 (Fig. 2 and Appendix Table 2). Furthermore, SSIs following hip arthro- plasties contributed 54% of the total SSIs following arthroplasties. Arthroplasty revisions accounted for 10% of all arthroplasties
(1,512,661 cumulative revisions across all years). From 2020 through 2030, the model projected revisions would increase 23% (Fig. 2 and Appendix Table 2). SSIs following revision increased by 21% and accounted for 26% of all SSIs (Figure 2 and Appendix Table 2). Most arthroplasties and SSIs were performed on patients aged
between 65 and 84 years. The percent of the total arthroplasties and SSIs increased between 2020 and 2030, from 52% and 59% of total arthroplasties and SSIs respectively in 2020 to 59% and 65% in 2030 (Fig. 3). (Table 1)
Fig. 2. Projected 2020 to 2030 complex surgical site infections (SSIs) following primary and revision hip and knee arthroplasties with 95% confidence intervals.
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