1186
Of these, 258 developed a complex infection within 90 days of arthroplasty: 145 following a hip replacement and 113 following a knee replacement. Therefore, the percentage who developed a complex infection was 1.04%: 1.48% for hips and 0.76% for knees. The most commonly identified pathogen for a complex SSI was S. aureus. We identified 94 cases of methicillin-sensitive S. aureus (MSSA) and 5 cases of MRSA, which accounted for 38% of all complex SSIs. A causative pathogen was not identified for ~9% of the complex SSIs. Death was significantly more common in the infected cohort
compared to the noninfected cohort (12% vs 3.8%; P < .0001). There was no significant difference in outmigration between the infected and noninfected cohorts (0.9% overall). Additionally, the proportion of patients with >2 Elixhauser comorbidities was sig- nificantly higher in the infected cohort (30.6% vs 20.5%; P < .001).
12- and 24-month costs
The 12-month costs were significantly higher in the infected versus noninfected cohort for hospitalizations, emergency room, day surgery, and day medicine visits. The total mean costs included initial arthroplasty and costs for admission at the time of infection for those in the infected cohort (Table 2). This was true for overall costs as well as when the specific ICD-10 codes were used for tracking costs. The costs at 24 months were not sub- stantially higher than the 12-month costs; overall the total mean cost at 24 months was $106,361 (IQR, 53,718–137,997) (US$ 76,043) for the infected cohort and $25,143 (IQR, 13,680– 25,538) (US$ 17,976) for the noninfected cohort. When only the ICD-10 codes related to infection were used to track costs, the 24-month cost was $74,294 (IQR, 37,209–89,252) (US$ 53,117) for the infected cohort and $13,565 (IQR, 10,269–13,162) (US$ 9,698) for the noninfected cohort. When the overall total mean costs at 12 months were divided
into subgroups, costs were all significantly higher in the infected versus the noninfected group (Table 3). The difference in costs between S. aureus and all other pathogens for the infected cohort can be found in Table 3. Overall, the costs of S. aureus infections following knee and hip arthroplasties were $99,765 (US$ 71,327) and $116,417 (US$ 83,232), respectively.
Adjusted costs
After adjustment for age, sex, First Nations status, and patient comorbidities, the total mean costs at 12 months for the infected and noninfected cohorts were $94,183 and $13,204, respectively (US$ 67,336 and US$ 9,440). When considering only hospita- lization and emergency room, day surgery, and day medicine visits for infection-related ICD-10 codes, the total mean costs at 12 months for the infected and noninfected cohorts were $69,699 and $13,203, respectively (US$ 49,831 and US$ 9,440). Infection, advancing age (≥65 years), hip replacement, con- gestive heart failure, diabetes with chronic complications, renal failure, and increasing number of Elixhauser comorbidities were associated with increased 1-year costs (Table 4).
Length of stay
The mean LOS at time of initial arthroplasty was 5.1 days for those who subsequently developed a complex SSI versus 3.8 days for those who did not. Overall, the mean LOS for all hospital visits after the initial arthroplasty, in the first year for patients who developed an infection was 38.9 days (36.9 and 40.5 days for knee
Elissa D. Rennert-May et al
Table 2. Mean Overall and Infection Related Costs Including Interquartile Range (IQR) Over 12 Months for Patients With and Without Complex Surgical Site Infection
Variable Cost of initial arthroplasty
Cost of admission at time of infection
Overall 1-year mean costs Hospitalization costs
Emergency room, day surgery and day medicine costs
Total Mean costb
Infection related 1-year mean costs Hospitalization costs
Emergency room, day surgery, and day medicine costs
Total mean costb
Infected Cohort, $ (IQR)a
14,071
(10,400–14,202) 16,870
(0 –22,331) 54,499
(18,113–73,653) 9,881
(4,635–12,758) 95,321
4,351 (0–0)
3,340 (1,453–4,089) 19,893 (49,623–120,636) (12,610–19,723) 38,397
(13,060–48,876) 1,106
(369–1,490) 70,144 (35,923–86,368) 953 (0–0)
38 (0–0)
13,195 (10,269–13,049) aMann-Whitney U P values <.001 for all comparisons in the table between overall 1-year
mean costs and infection related 1-year mean costs. bThese total mean costs include initial arthroplasty cost, cost of admission at time of infection (for the infected cohort), hospitalization costs, and emergency room, day surgery, and day medicine costs.
and hip, respectively), compared to 3.4 days (3.2 and 3.7 days for knee and hip, respectively) for the noninfected group (P < .001). When considering only hospitalizations for infection related ICD-10 codes, the mean LOS for hospital visits outside of the initial arthroplasty at 1 year was 28 days (27.9 and 28.1 days for knee and hip, respectively) versus 1.0 days (0.8 and 1.1 days for knee and hip, respectively) for the infected and noninfected cohorts, respectively (P < .001). For those who did develop a complex SSI, the mean LOS for those with an S. aureus infection was 15.4 days compared to all other pathogens, for which the mean LOS was 12.2 days.
Discussion
We observed significantly higher 1-year healthcare costs for those who developed a complex SSI following primary hip or knee arthroplasty, considering either total healthcare costs ($95,321 vs $19,893; P < .001 (US$ 68,150 vs US$ 14,223)), or only the subset of costs related to infection-related hospitalizations and emer- gency room, day surgery, and day medicine visits ($70,144 vs $13,195; P < .001 (US$ 52,043 vs US$ 9,790)). After adjusting for age, sex, First Nations status, and medical comorbidities, higher 1-year costs were associated with a higher number of Elixhauser comorbidities as well as diabetes with chronic complications, metastatic cancer, and renal failure. Our results are similar to 2 prior studies completed in the
United States, one looking at the economic burden associated with SSI following knee arthroplasty,20 and one examining the
Noninfected Cohort, $ (IQR)
12,203
(10,269–12,562) ...
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