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BACKGROUND: Studies have examined the effects of temperature on mortality in a single city, country, or region. However, less evidence is available on the variation in the associations between temperature and mortality in multiple countries, analyzed simultaneously. METHODS: We obtained daily data on temperature and mortality in 306 communities from 12 countries/regions (Australia, Brazil, Thailand, China, Taiwan, Korea, Japan, Italy, Spain, United Kingdom, United States, and Canada). Two-stage analyses were used to assess the nonlinear and delayed relation between temperature and mortality. In the first stage, a Poisson regression allowing overdispersion with distributed lag nonlinear model was used to estimate the community-specific temperature-mortality relation. In the second stage, a multivariate meta-analysis was used to pool the nonlinear and delayed effects of ambient temperature at the national level, in each country. RESULTS: The temperatures associated with the lowest mortality were around the 75th percentile of temperature in all the countries/regions, ranging from 66th (Taiwan) to 80th (UK) percentiles. The estimated effects of cold and hot temperatures on mortality varied by community and country. Meta-analysis results show that both cold and hot temperatures increased the risk of mortality in all the countries/regions. Cold effects were delayed and lasted for many days, whereas heat effects appeared quickly and did not last long. CONCLUSIONS: People have some ability to adapt to their local climate type, but both cold and hot temperatures are still associated with increased risk of mortality. Public health strategies to alleviate the impact of ambient temperatures are important, in particular in the context of climate change.

Winds from the Sahara-Sahel desert region regularly transport large amounts of dust to the Americas, North Africa, and Europe. The presence of high dust concentrations for long periods of time, and the interaction between dust and man-made air pollution, raise concerns about adverse health effects and appropriate interventions by health authorities. This study tested the hypothesis that outbreaks of Saharan dust exacerbate the effects of man-made pollution, specifically fine and coarse particulate matter (PM2.5 and PM10-2.5, respectively) on daily mortality.We investigated the effects of exposure to PM10-2.5 and PM2.5 between March 2003 and December 2004 in Barcelona (Spain) on daily mortality; changes of effects between Saharan and non-Saharan dust days were assessed using a time-stratified case-crossover design. We studied the chemical composition of particulate matter to explain changes of effects.The study included 24,850 deaths. During Saharan dust days, a daily increase of 10 microg/m3 of PM10-2.5 increased daily mortality by 8.4% (95% confidence interval = 1.5%-15.8%) compared with 1.4% (-0.8% to 3.4%) during non-Saharan dust days (P value for interaction = 0.05). In contrast, there was no increased risk of daily mortality for PM2.5 during Saharan dust days. Although coarse particles seem to be more hazardous during Saharan dust days, differences in chemical composition did not explain these observations.Saharan dust outbreaks may have adverse health effects. Further investigation is needed to understand the role of coarse particles and the mechanism by which Saharan dust increases mortality.