Population aging and changing hospitalization risks in Germany: a decomposition of changes in inpatient cases, 2005–2021

BACKGROUND: Inpatient care improves and maintains population health but requires a clear understanding of the drivers of inpatient care utilization. In Germany, inpatient cases increased from 16.5 to 19.4 million between 2005 and 2019 and dropped tremendously during the Covid-19 pandemic. We investigate how population aging and changing hospitalization risks in the German population contributed to the changes in inpatient case numbers remunerated according to the German Diagnosis-Related Groups (G-DRG) system between 2005 and 2021. METHODS: The analysis is based on more than 280 million cases from the G-DRG Statistic and population exposures from the Human Mortality Database and covers all ages from 0 to 95+. We employ the Total Hospitalization Rate (THR) as the outcome, which measures total inpatient case numbers in relation to the changing population size. Using Kitagawa decomposition techniques, we quantify the impact of population aging and changes in age-specific hospitalization risks on THR changes before and during the Covid-19 pandemic, for the total population, women and men. To consider disease-specific influences on the age-specific hospitalization risks, we stratified the hospitalization risk effect by the disease category of the underlying primary diagnosis. RESULTS: The THR experienced two distinct periods of change, increasing from 2005 to 2014 and decreasing afterwards, with a further drop related to the onset of the Covid-19 pandemic. Between 2005 and 2019, 64% of the increase in the THR can be attributed to the changing age structure. Population aging led to an increase in inpatient cases throughout the observation period, whereas the effect of changing age-specific hospitalization risks reversed from an increase in cases between 2005 and 2014 to a decrease in cases between 2014 and 2021. This trend shift has offset the effects of population aging since 2014 and was excessively strong during the Covid-19 pandemic. The decline in age-specific hospitalization risks across many disease categories underlines that no specific health conditions are responsible for the trend change in hospitalization risks. CONCLUSIONS: Our findings demonstrate the importance of population aging for inpatient case numbers. Future hospital planning needs to consider the central role of population aging in shaping inpatient care needs.