Introduction: The optimal distribution of burn centers remains unclear. We aimed to determine the appropriate number of burn centers per population (density) and examined a nationwide registry with the hypothesis that low-density burn centers would be associated with unfavorable outcomes. Patients and methods: A retrospective study was conducted using the Japanese Society of Burn Injury registry (2011–2021). Burn center density was defined as the number of burn centers per one million population in each prefecture, and centers were trisected on the basis of density. Hospital-free days until day 30 were compared between patients at high-, middle-, and low-density centers. Inverse probability weighting was conducted to adjust baseline characteristics, including age, burn mechanism, and burn severity. Results: We included 6764, 6209, and 2200 patients at high-, middle-, and low-density burn centers, respectively. After adjusting for patient demographics and burn severity, patients at high- and middle-density centers (≥0.4 centers per one million population) had longer hospital-free days compared with those at low-density centers (11 [0–23] vs 11 [0–23] vs 8 [0–22] days; p < 0.001). Conclusions: Low burn center density (<0.4 centers per one million population) was associated with longer hospital stay, whereas no higher limit was determined.
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