Analysis of intra-annual mortality fluctuations by cause of death in Italy, 2004-19.

Seasonal fluctuations in mortality significantly affect population health and remain an important public health challenge, particularly in the context of climate change and population ageing. Evidence on how different causes of death shape seasonal mortality patterns remains limited. We apply a novel framework to quantify, in a systematic, transparent, and comparable manner, the absolute and relative contributions of 17 cause-of-death groups to seasonal mortality in Italy. We analyzed monthly mortality data from the Italian National Institute of Statistics, disaggregated by cause of death, sex, and 5-year age groups, 2004-19. Excess mortality for 17 major causes of death was quantified by comparing the observed age-standardized death rate (SDR) with the baseline SDR, defined as the average of the 3 months with the lowest mortality each year. Heart and respiratory diseases were the leading contributors to excess mortality, accounting for approximately 40% and 15% of the intra-annual burden, respectively. The summer months exhibited significantly smaller excess mortality. Respiratory diseases showed the highest relative impact compared to the other causes of death. While baseline mortality decreased over time, the relative intra-annual burden remained stable or increased for specific causes, indicating persistent or growing seasonal vulnerabilities. Intra-annual mortality fluctuations in Italy were mainly driven by cardiovascular and respiratory diseases and have remained stable over time despite improvements in overall mortality. These persistent patterns highlight unmet seasonal vulnerabilities and the importance of integrating cause-specific seasonality into health planning, particularly in light of ageing populations and climate change challenges.