With an ageing population, understanding leading causes of hospitalisation in older adults is critical for care strategies. These leading causes may vary across residential settings and by seasonal patterns. This study examines the temporal trends of leading causes of hospitalisation among older adults in community-dwelling and nursing home settings, specifically comparing patterns during winter and summer seasons.

A retrospective analysis of electronic medical records from Hong Kong public hospitals (2012–2018) was conducted for three million adults aged ≥65. Age-standardised and sex-standardised monthly hospitalisation rates and average annual percentage change (AAPC, representing the average yearly percentage change in rates) were examined for leading causes during summer and winter across settings.

Among community-dwelling individuals, the top five causes in 2018 were symptoms, signs and abnormalities not classified elsewhere (NEC), neoplasms, genitourinary, circulatory and respiratory diseases in winter, with digestive diseases replacing respiratory diseases in summer. Symptoms, signs and abnormalities NEC (AAPC: 2.7% (95% CI 1.8% to 3.6%) in winter; 3.4% (2.8% to 4.0%) in summer), neoplasms (2.4% (1.4% to 3.4%) in winter; 2.5% (1.6% to 3.4%) in summer), genitourinary (2.5% (2.1% to 2.9%) in winter; 2.4% (1.8% to 3.0%) in summer) and digestive diseases (2.5% (1.6% to 3.3%) in winter; 2.6% (1.7% to 3.5%) in summer) increased, while circulatory diseases decreased in winter. In nursing home residents, the top five causes in 2018 were respiratory diseases, symptoms, signs and abnormalities NEC, genitourinary, circulatory and digestive diseases in winter and summer. Symptoms, signs and abnormalities NEC increased (2.9% (0.9% to 5.0%) in winter; 2.9% (0.8% to 5.1%) in summer), while circulatory diseases declined across seasons. Genitourinary diseases remained stable across seasons, whereas digestive diseases declined in winter.

In Hong Kong’s ageing population, seasonal and temporal shifts in hospitalisation causes were observed. Symptoms, signs and abnormalities NEC emerged as the top two causes across settings, highlighting challenges for primary care and hospital management and need for enhanced prevention and care strategies.