High temperature effect on daily all-cause mortality in Tunis 2005-2007

The relationship between thermal stress and health has been only marginally investigated in North Africa. This study aimed to estimate the short-term effect of heat on total mortality, in the city of Tunis in 2005-2007, using time series analysis.

The study period was restricted to the summer season (May-October) and heat effect was assessed using maximum temperature as exposure variable. We estimated the breakpoint above which heat-related mortality begins to increase using a segmented linear regression. A Poisson Generalized Estimating Equations (GEE) model was then used to estimate the impact of heat on daily mortality. Models were adjusted for nitrogen dioxide (NO₂), trend, calendar month, day of the week, the Ramadan period, and holidays.

The estimated breakpoint was 31.5°C (standard deviation: 0.9°C). After adjustment for potential confounders, the daily mortality increased significantly by 2.00% [95% confidence interval: 0.68-3.16] for a 1°C increase in daily maximum temperature above the breakpoint. An increase of 10mg/m³ in NO₂ was associated with a significant increase in daily mortality (0.48% [0.08-0.88]).

There is an important effect of heat on daily mortality in the city of Tunis. This is the first evaluation of such an association in a North African city with hot and dry summers and a lower middle economy.