Investigating the impact of influenza on excess mortality in all ages in Italy during recent seasons (2013/14 - 2016/17 seasons)

OBJECTIVES: In the recent years, Italy has been registering peaks in death rates, particularly among the elderly during the winter season. Influenza epidemics has been indicated as one of the potential determinants of such an excess. The objective of our study was to estimate the influenza-attributable contribution to excess mortality during the influenza seasons from 2013/14 to 2016/17 in Italy.

METHODS: We used the EuroMomo and the FluMomo methods, to estimate the annual trend of influenza-attributable excess death rate, by age group. Population data were provided by the National Institute of Statistics, data on influenza like illness and confirmed influenza cases were provided by the National Institute of Health. As indicator of weekly influenza activity (IA) we adopted the Goldstein index, that is the product of the percentage patients seen with influenza-like illness (ILI) and percentage of influenza-positive specimens, in a given week.

RESULTS: We estimated an excess deaths of 7,027, 20,259, 15,801 and 24,981 attributable to influenza epidemics in the 2013/14, 2014/15, 2015/16 and 2016/17, respectively, using the Goldstein index. The average annual mortality excess rate per 100,000 ranged from 11.6 to 41.2 with most of the influenza-associated deaths per year registered among elderly. However also children less than 5 years old reported a relevant influenza attributable excess death rate in the 2014/15 and 2016/17 season (1.05/100,000 and 1.54/100,000 respectively).

CONCLUSIONS: Over 68,000 deaths were attributable to influenza epidemics in the study period. The observed excess of deaths is not completely unexpected, given the high number of fragile very old subjects living in Italy. In conclusion, the unpredictability of the influenza virus continues to present a major challenge to health professionals and policy makers. Nonetheless, vaccination remains the most effective means for reducing the burden of influenza, and efforts to increase vaccine coverage and the introduction of new vaccine strategies (such as vaccinating healthy children) should be considered to reduce the influenza attributable excess mortality experienced in Italy and in Europe in the last seasons.