The seasonality of total hospitalizations in Ontario by age and gender: a time series analysis.

BACKGROUND Consistent and predictable seasonal fluctuations in hospitalizations have been demonstrated for diverse communicable and non-communicable health conditions. The objective of this study was to examine the seasonal patterns of all hospitalizations by age and gender in order to determine whether the hospital system for a large geographical area was subject to consistent, predictable temporal variations. METHODS A retrospective population-based study of approximately 14 million residents of Ontario was conducted to assess temporal patterns in all hospitalizations from April 1, 1988 to March 31, 2000. Time series analysis, using spectral analysis, was conducted to assess seasonal variations and trends over time and to account for autocorrelation. RESULTS Conspicuous seasonality in hospitalizations was found in every age group for both sexes with the exception of males between the ages of 20 and 39. The average monthly variability ranged from lows of 15% for the age group 20-29 for both sexes, to highs of 34% in males between 5 and 9 years. For the total population, this represents a 12-year average variability of approximately 20% or 20,000 out of 97,000 hospitalizations. For both sexes, peak hospitalizations typically occurred in the spring and autumn for the youngest and oldest age groups, and in January for the middle age groups. CONCLUSION Seasonal factors play an important role in the utilization of hospital services in Ontario. The determinants of this seasonality, which include environmental and social/behavioural factors, are not well understood.