Comorbidity and risk of infection among patients with hip fracture: a Danish population-based cohort study

SUMMARY: Impact of comorbidity on infection risk among hip fracture patients is unclear. We found high incidence of infection. Comorbidity was an important risk factor for infection up to 1 year after surgery. Results indicates a need for additional investment in pre- and postoperative programs that assist patients with high comorbidity. PURPOSE: Comorbidity level and incidence of infection have increased among older patients with hip fracture. The impact of comorbidity on infection risk is unclear. We conducted a cohort study examining the absolute and relative risks of infection in relation to comorbidity level among hip fracture patients. METHODS: Utilizing Danish population-based medical registries, we identified 92,600 patients aged ≥ 65 years undergoing hip fracture surgery between 2004 and 2018. Comorbidity was categorized by Charlson comorbidity index scores (CCI): none (CCI = 0), moderate (CCI = 1–2), or severe (CCI ≥ 3). Primary outcome was any hospital-treated infection. Secondary outcomes were hospital-treated pneumonia, urinary tract infection, sepsis, reoperation due to surgical-site infection (SSI), and a composite of any hospital- or community-treated infection. We calculated cumulative incidence and hazard ratios (aHRs) adjusted for age, sex, and surgery year, including 95% confidence intervals (CIs). RESULTS: Prevalence of moderate and severe comorbidity was 40% and 19%, respectively. Incidence of any hospital-treated infection increased with comorbidity level within 0–30 days (none 13% vs. severe 20%) and 0–365 days (none 22% vs. 37% severe). Patients with moderate and severe comorbidity, compared to no comorbidity, had aHRs of 1.3 (CI: 1.3–1.4) and 1.6 (CI: 1.5–1.7) within 0–30 days, and 1.4 (CI: 1.4–1.5) and 1.9 (CI: 1.9–2.0) within 0–365, respectively. Highest incidence was observed for any hospital- or community-treated infection (severe 72%) within 0–365 days. Highest aHR was observed for sepsis within 0–365 days (severe vs. none: 2.7 (CI: 2.4–2.9)). CONCLUSION: Comorbidity is an important risk factor for infection up to 1 year after hip fracture surgery. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00198-023-06823-6.