Comparison of hot and cold spell effects on cardiovascular mortality in individual population groups in the Czech Republic

We compared the effects of hot and cold spells on cardiovascular mortality in the Czech Republic over 1986-2006 and examined differences between population groups. We used analogous definitions for hot and cold spells that are based on quantiles of daily average temperature anomalies and do not incorporate any location-specific threshold. Epidemics of influenza/acute respiratory infections were identified, and corresponding periods were excluded from the analysis. Both hot and cold spells are associated with significant excess cardiovascular mortality. The effects of hot spells are more direct (unlagged) and typically concentrated in a few days of a hot spell, while cold spells are associated with indirect (lagged) mortality impacts persisting after a cold spell ends. Although the mortality peak is less pronounced for cold spells, the cumulative magnitude of excess mortality is larger for cold than hot spells. Gender differences consist mainly of much larger excess mortality of females in hot spells and more lagged effects in females than males associated with cold spells. Effects of hot spells have a similar temporal pattern in all age groups but much larger magnitude in the elderly. For cold spells, by contrast, relative excess mortality is largest in the middle-aged population (25-59 yr). The results suggest that mechanisms playing the dominant role in inducing cold-related mortality differ between this age group (in which the effects are unlagged) and older age groups (significant excess mortality at lags of around 7 d and longer). For both high and low temperature extremes, the formulation of preventive measures (implemented by means of warning systems and biometeorological forecast alerts) should take into account the varied effects in individual population groups.