Short-term effects of particulate matter on mortality during forest fires in Southern Europe: Results of the MED-PARTICLES project

Background: An association between occurrence of wildfires and mortality in the exposed population has been observed in several studies with controversial results for cause-specific mortality. In the Mediterranean area, forest fires usually occur during spring-summer, they overlap with Saharan outbreaks, are associated with increased temperature and their health effects are probably due to an increase in particulate matter. Aim and methods: We analysed the effects of wildfires and particulate matter (PM<inf>10</inf>) on mortality in 10 southern European cities in Spain, France, Italy and Greece (2003-2010), using satellite data for exposure assessment and Poisson regression models, simulating a case-crossover approach. Results: We found that smoky days were associated with increased cardiovascular mortality (lag 0-5, 6.29%, 95% CIs 1.00 to 11.85). When the effect of PM<inf>10</inf> (per 10 mg/m³) was evaluated, there was an increase in natural mortality (0.49%), cardiovascular mortality (0.65%) and respiratory mortality (2.13%) on smoke-free days, but PM<inf>10</inf>-related mortality was higher on smoky days (natural mortality up to 1.10% and respiratory mortality up to 3.90%) with a suggestion of effect modification for cardiovascular mortality (3.42%, p value for effect modification 0.055), controlling for Saharan dust advections. Conclusions: Smoke is associated with increased cardiovascular mortality in urban residents, and PM<inf>10</inf> on smoky days has a larger effect on cardiovascular and respiratory mortality than on other days.