Out-of-Municipality Long-Term Care Insurance Benefits and Public Hospital Revenue Patterns in the Remote Oki Islands, Japan: An Exploratory Ecological Study.

Background Population aging and depopulation pose substantial challenges to the sustainability of healthcare and long-term care systems in rural and remote communities. This study aimed to describe temporal trends in out-of-municipality long-term care insurance (LTCI) benefits and contemporaneous public hospital management indicators in two remote island areas in Japan. Methods We conducted an exploratory descriptive ecological study using aggregated municipality-level LTCI and population data and hospital-level management data from fiscal year (FY) 2015 to FY2023 in the Oki Islands, Shimane Prefecture, Japan. We described trends in the Dozen region and Okinoshima Town, including population structure, the proportion of out-of-municipality LTCI benefits, inpatient and outpatient revenue, bed occupancy rates, and financial indicators. Percentage changes, annualized percentage changes, and outpatient-to-inpatient revenue ratios were calculated descriptively. No inferential hypothesis testing was performed. Results The population decreased in both areas. In the Dozen region, the proportion of out-of-municipality LTCI benefits increased overall from 9.5% in FY2015 to 21.9% in FY2023, whereas it remained relatively stable in Okinoshima Town, ranging from 2.6% to 3.2%. In Dozen Hospital, inpatient revenue decreased from JPY 330.8 million to JPY 260.6 million (-21.2%), while outpatient revenue increased from JPY 226.0 million to JPY 267.9 million (+18.6%). In Oki Hospital, inpatient revenue decreased from JPY 1,294.3 million to JPY 1,082.5 million (-16.4%), while outpatient revenue increased from JPY 1,035.5 million to JPY 1,116.2 million (+7.8%). The outpatient-to-inpatient revenue ratio increased from 0.68 to 1.03 in Dozen Hospital and from 0.80 to 1.03 in Oki Hospital. Conclusions The increase in out-of-municipality LTCI benefits in the Dozen region coincided with a comparatively large shift in the composition of Dozen Hospital revenue from inpatient toward outpatient services. These hypothesis-generating ecological findings do not demonstrate individual relocation or establish a causal relationship. Out-of-municipality LTCI benefits may warrant further evaluation as an administrative indicator alongside individual-level care utilization, residential histories, service capacity, and patient-flow data before being used to inform health policy or resource allocation.