tetano
Editor, Senior Moderator
[h=2]Mortality attributable to seasonal influenza in Greece, 2013 to 2017: variation by type/subtype and age, and a possible harvesting effect
[/h]
Introduction
Go to section...
Seasonal influenza is a considerable public health problem worldwide. A 2018 modelling study estimated that 291,000?646,000 annual deaths globally are attributable to influenza, most of those in older adults [1]. The impact of influenza on mortality can vary widely each year and across different populations, due to factors such as the types/subtypes of circulating viruses, the age structure of the population, its level of health and access to healthcare, and its degree of immunity due to vaccination or previous influenza epidemics [2,3].
There is intense interest in obtaining accurate and timely estimates of influenza-attributable mortality across all age groups, in order to inform public health policy and evaluate the effectiveness of preventive interventions. Numerous studies have attempted to assess influenza-attributable mortality, mostly in high-income countries, and with heterogeneous results [4]. Differences in study methodology are important contributors to this heterogeneity, besides actual host- and pathogen-related factors [4].
The variety in the employed methods is a reflection of the many challenges involved in accurately estimating the part of population mortality that is attributable to influenza. First, the types/subtypes of circulating influenza viruses need to be taken into account in any statistical model, as not all types/subtypes may have the same effects on all age groups [5]. This highlights the need to have solid laboratory data to inform an influenza activity proxy, as models without such a proxy tend to produce higher mortality estimates [4]. Second, estimation needs to adjust for the confounding effect of ambient temperature, not only at the extremes but also at milder cold levels, which may account for substantially more temperature-related deaths than extreme cold [6]. Finally, the association between influenza circulation and mortality is characterised by a lag that cannot be assumed to be fixed; not all people die at the same time after falling ill with influenza, therefore the effect of a given level of influenza activity on mortality is likely to be distributed over a period of time. Such distributed-lag associations with mortality have been previously described for temperature [6] and air pollution [7], but are also likely for influenza as well. To our knowledge though, very few studies to date have attempted to account for the lag dimension in the association between influenza and mortality [8-11], despite the availability of powerful relevant methods [12].
The objective of the current study was to examine the mortality attributable to influenza over four winter seasons in Greece, and across different age groups, while addressing the methodological issues outlined above. For this purpose we combined epidemiological, virological and mortality data routinely collected as part of public health surveillance, with temperature data covering the entire country. A secondary objective was to compare the mortality attributable to cold temperatures with that attributable to influenza, in order to assess which one is the primary driver of excess winter deaths [13,14].
...
full article
https://www.eurosurveillance.org/content/10.2807/1560-7917.ES.2019.24.14.1800118
- Theodore Lytras[SUP]1[/SUP], Katerina Pantavou[SUP]2[/SUP], Elisavet Mouratidou[SUP]1[/SUP], Sotirios Tsiodras[SUP]1,3[/SUP]
Introduction
Go to section...
Seasonal influenza is a considerable public health problem worldwide. A 2018 modelling study estimated that 291,000?646,000 annual deaths globally are attributable to influenza, most of those in older adults [1]. The impact of influenza on mortality can vary widely each year and across different populations, due to factors such as the types/subtypes of circulating viruses, the age structure of the population, its level of health and access to healthcare, and its degree of immunity due to vaccination or previous influenza epidemics [2,3].
There is intense interest in obtaining accurate and timely estimates of influenza-attributable mortality across all age groups, in order to inform public health policy and evaluate the effectiveness of preventive interventions. Numerous studies have attempted to assess influenza-attributable mortality, mostly in high-income countries, and with heterogeneous results [4]. Differences in study methodology are important contributors to this heterogeneity, besides actual host- and pathogen-related factors [4].
The variety in the employed methods is a reflection of the many challenges involved in accurately estimating the part of population mortality that is attributable to influenza. First, the types/subtypes of circulating influenza viruses need to be taken into account in any statistical model, as not all types/subtypes may have the same effects on all age groups [5]. This highlights the need to have solid laboratory data to inform an influenza activity proxy, as models without such a proxy tend to produce higher mortality estimates [4]. Second, estimation needs to adjust for the confounding effect of ambient temperature, not only at the extremes but also at milder cold levels, which may account for substantially more temperature-related deaths than extreme cold [6]. Finally, the association between influenza circulation and mortality is characterised by a lag that cannot be assumed to be fixed; not all people die at the same time after falling ill with influenza, therefore the effect of a given level of influenza activity on mortality is likely to be distributed over a period of time. Such distributed-lag associations with mortality have been previously described for temperature [6] and air pollution [7], but are also likely for influenza as well. To our knowledge though, very few studies to date have attempted to account for the lag dimension in the association between influenza and mortality [8-11], despite the availability of powerful relevant methods [12].
The objective of the current study was to examine the mortality attributable to influenza over four winter seasons in Greece, and across different age groups, while addressing the methodological issues outlined above. For this purpose we combined epidemiological, virological and mortality data routinely collected as part of public health surveillance, with temperature data covering the entire country. A secondary objective was to compare the mortality attributable to cold temperatures with that attributable to influenza, in order to assess which one is the primary driver of excess winter deaths [13,14].
...
full article
https://www.eurosurveillance.org/content/10.2807/1560-7917.ES.2019.24.14.1800118