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Winter Mortality in Bourgogne-Franche-Comté

An analysis of all-cause mortality is conducted weekly at the national and regional levels, based on vital statistics data from approximately 3,000 French municipalities, which account for nearly 80% of all deaths. The expected weekly number of deaths is estimated by Santé publique France using the statistical model developed as part of the European EuroMomo project and used by 19 European countries, taking into account historical data over 6 years, the general trend, and seasonal fluctuations. These mortality data (administrative) provided by INSEE do not include information on causes of death. However, influenza is known to contribute significantly to the rise in winter mortality, particularly when the A(H3N2) virus is circulating, which has a particularly severe impact on the elderly (see PE 2017/10). This was the case with this winter’s influenza epidemic, which was dominated by this virus and lasted approximately ten weeks (from December 5, 2016, to February 12, 2017): an estimated 21,200 excess deaths compared to expected mortality during this period were recorded. This figure is comparable to that of the 2014–2015 winter (18,300 excess deaths), during which the A(H3N2) virus was dominant. According to a recent statistical model, approximately 14,400 of these 21,200 deaths (68%) are attributable to influenza.In Bourgogne-Franche-Comté (see figure), as in other metropolitan regions, mortality is typically higher during the winter months (red curve, which follows natural fluctuations in mortality), with marked and significant increases (above the statistical threshold shown in green). This excess mortality is evident during the winter of 2016–2017 (1,550 excess deaths from all causes over the 10-week epidemic period compared to the expected number, with a peak during the first two weeks of January), coinciding with the influenza epidemic and other winter epidemics (bronchiolitis, gastroenteritis). This excess was also observed during the winter of 2014–2015, but not in 2013–2014 and only slightly in 2015–2016 (a winter during which the flu epidemic occurred late). This excess was also observed in the summer, from June 29 to July 19, following the 2015 heat wave. The proportion attributable to influenza cannot be calculated precisely at the regional level, but the national estimate confirms that a large majority of excess deaths in Bourgogne-Franche-Comté this winter were linked to the influenza epidemic. However, other factors must be considered to explain this excess mortality: first, a proportion of elderly people higher than the national average in our region, which explains why the impact of the flu on mortality may be greater than in other regions; second, the impact of other factors cannot be ruled out (circulation of the respiratory syncytial virus responsible for bronchiolitis and respiratory infections, air pollution, etc.), and finally, cold weather may also play a role in winter, just as heat does in summer, in our continental climate zone (Grand Est, Bourgogne-Franche-Comté, Auvergne-Rhône-Alpes).