Table 3 Results of the generalized linear mixed model analysis in which patient volume was included as a categorical variable (≤ 5 or > 5)
Population of severe burn patients adjusted by the prognostic burn index | ||||||
 Primary outcome | Hospitals with annual patients ≤ 5, n (%) | Hospitals with annual patients > 5, n (%) | Crude odds ratio (95% CI) | p value | Adjusted odds ratio (95% CI) | p value |
  In-hospital mortality | 768 (21.1) | 519 (32.4) | 1.80 (1.58–2.05) | < 0.001 | 1.85 (1.42–2.41) | < 0.001 |
 Secondary outcomes | Hospitals with annual patients ≤ 5, median [IQR] | Hospitals with annual patients > 5, median [IQR] | Crude difference (95% CI) | p value | Adjusted difference (95% CI) | p value |
  Total healthcare costs per admission, USD | 19,500 [6510, 48,618] | 35,400 [11,600, 88,034] | 27,141 (25,132–29,151) | < 0.001 | 29,564 (26,237–32,890) | < 0.001 |
  Hospital-free days at 90 days, days | 37 [0, 71] | 3 [0, 53] | − 12.2 (− 13.2 to − 11.2) | < 0.001 | −15.4 (− 17.9 to − 13.0) | < 0.001 |
Population who were directly transported from the scene of injury adjusted by the prognostic burn index | ||||||
 Primary outcome | Hospitals with annual patients ≤ 5, n (%) | Hospitals with annual patients > 5, n (%) | Crude odds ratio (95% CI) | p value | Adjusted odds ratio (95% CI) | p value |
  In-hospital mortality | 792 (26.1) | 225 (33.1) | 1.40 (1.17–1.68) | < 0.001 | 1.40 (0.97–2.02) | 0.072 |
 Secondary outcomes | Hospitals with annual patients ≤ 5, median [IQR] | Hospitals with annual patients > 5, median [IQR] | Crude difference (95% CI) | p value | Adjusted difference (95% CI) | p value |
  Total healthcare costs per admission, USD | 20,657 [6645, 54,832] | 32,934 [9553, 83,600] | 23,169 (20,369–25,969) | < 0.001 | 24,677 (20,236–29,119) | < 0.001 |
  Hospital-free days at 90 days, days | 27 [0, 68] | 0 [0, 54] | − 8.5 (− 9.9 to − 7.1) | < 0.001 | − 11.8 (− 15.3 to − 8.3) | < 0.001 |
Population whose prognostic burn index ≥ 120 adjusted by the prognostic burn index | ||||||
 Primary outcome | Hospitals with annual patients ≤ 5, n (%) | Hospitals with annual patients > 5, n (%) | Crude odds ratio (95% CI) | p value | Adjusted odds ratio (95% CI) | p value |
  In-hospital mortality | 600 (16.6) | 276 (23.9) | 1.57 (1.34–1.85) | < 0.001 | 1.77 (1.31–2.38) | < 0.001 |
 Secondary outcomes | Hospitals with annual patients ≤ 5, median [IQR] | Hospitals with annual patients > 5, median [IQR] | Crude difference (95% CI) | p value | Adjusted difference (95% CI) | p value |
  Total healthcare costs per admission, USD | 21,565 [7193, 52,228] | 37,724 [15,388, 87,400] | 25,201 (22,995–27,408) | < 0.001 | 29,976 (26,068–33,885) | < 0.001 |
  Hospital-free days at 90 days, days | 41 [0, 71] | 19 [0, 57.25] | − 10.5 (− 11.6 to − 9.4) | < 0.001 | − 15.3 (− 18.0 to − 12.6) | < 0.001 |
Cohort of severe burn patients who survived for more than 2 days of admission adjusted by the developed risk adjustment model | ||||||
 Primary outcome | Hospitals with annual patients ≤ 5, n (%) | Hospitals with annual patients > 5, n (%) | Crude odds ratio (95% CI) | p value | Adjusted odds ratio (95% CI) | p value |
  In-hospital mortality | 615 (17.1) | 341 (25.6) | 1.66 (1.43–1.93) | < 0.001 | 0.97 (0.71–1.33) | 0.853 |
 Secondary outcomes | Hospitals with annual patients ≤ 5, median [IQR] | Hospitals with annual patients > 5, median [IQR] | Crude difference (95% CI) | p value | Adjusted difference (95% CI) | p value |
  Total healthcare costs per admission, USD | 22,516 [7668, 53,255] | 39,157 [16,339, 94,715] | 27,999 (25,805–30,192) | < 0.001 | 22,750 (16,969–28,530) | < 0.001 |
  Hospital-free days at 90 days, days | 40 [0, 71] | 17.5 [0, 57.25] | −10.6 (−11.6 to − 9.6) | < 0.001 | − 7.3 (− 8.7 to − 5.8) | < 0.001 |