Long-Term Impact of Moscow Heat Wave and Wildfires on Mortality

To the Editor: In the summer of 2010, most of the European part of Russia suffered a heat wave that was unprecedented both in strength and duration, which led to 55,000 excess deaths during this period.1 In Moscow alone, an estimated 10,900 excess deaths from non-accidental causes occurred during the 44-day heat wave and a shorter smog episode caused by wildfires around the city.2 Although the short-term forward mortality displacement (typically within 15 or 30 days after heat stress) has been well described,3,4 there are few publications on long-term health consequences of heat waves. It has been proposed that the mortality displacement (ie, the ratio between the deficit after the heat event and the excess during the event) diminishes with the event’s strength, but the strongest heat events are likely to have pronounced long-term consequences.5 For example, the displacement within 1 year after the 2003 heat wave in France was about 20%.6 The aim of our study was to describe the temporal distribution of the displaced deaths after the Moscow 2010 heat wave, and to estimate the mortality displacement within any period until the end of 2012. We also conducted analyses stratified by age and cause of death to identify the main drivers of the mortality displacement. To estimate the difference between the observed and the expected number of daily deaths during and after the heat wave, a predictive model was developed, as described in eAppendix (https://links.lww.com/EDE/A874). We also used the annual mortality data from neighboring Saint Petersburg for comparison (eFigure 1, https://links.lww.com/EDE/A874).7 The Figure shows observed and expected deaths between 2009 and 2012 in Moscow. A major deficit in mortality occurred from the beginning of October until the end of the year of the heat wave. The deficit seemed to continue during 2011, after which there was an excess mortality in 2012. The cumulative excess mortality is illustrated in eFigure 2 (https://links.lww.com/EDE/A874). Non-accidental cumulative excess mortality reached its maximum of 11,300 (95% confidence interval [CI] = 10,800–11,800) almost 2 months after the end of the heat wave. A prolonged period of steady decline in cumulative excess mortality continued for 15 months after this date until the end of 2011, when the minimum of 5800 (1500–10,100) deaths was recorded. The mortality displacement during this period was 49% (95% CI = 11%–87%). In other words, about one-half of all excess deaths during the heat wave were forward-displaced for the period ranging from 2 to 17 months. Since January 2012, cumulative excess mortality began to increase again and the magnitude of harvesting diminished to 14% (0%–67%) by the end of 2012.FIGURE: Daily excess mortality from non-accidental causes in Moscow in 2009–2012. Red bar marks the heat wave period.Stratified analyses showed that the ratio of deaths among those aged 60 and over relative to those below 60 peaked during the heat wave and did not return to the pre-heat wave levels during 2012 (eFigure 3, https://links.lww.com/EDE/A874). The ratio of cardiovascular to non-cardiovascular mortality also increased during the heat wave, but showed a gradual decrease compared with the period before the heat wave. This indicates that the increase in deaths in 2012 was due to causes other than cardiovascular causes. In conclusion, marked mortality displacement was observed as a result of the 2010 heat wave in Moscow. This amounted to around half of all excess deaths during the heat wave; this displacement occurred mainly within few months, but extended for a longer period. The excess mortality observed after about 18 months following the end of the heat wave may indicate persistent long-term effects of the heat wave and smog episode, but it could also result from inaccurate projections of expected deaths. Dmitry ShaposhnikovBoris Revich Institute of Economic Forecasting Russian Academy of Sciences Moscow, Russia [email protected] Tom Bellander Getahun Bero Bedada Matteo Bottai Institute of Environmental Medicine Karolinska Institutet Stockholm, Sweden Tatyana Kharkova Ekaterina Kvasha Institute of Demography Higher School of Economics Moscow, Russia Tomas Lind Göran Pershagen Institute of Environmental Medicine Karolinska Institutet Stockholm, Sweden