The trend of transitional age structure underestimates influenza excess mortality in Mongolia
Session I – Nukiwa, Nao – Poster Only
Title of Contribution: The trend of transitional age structure underestimates influenza excess mortality in Mongolia
Author(s): Nao Nukiwa1, Alexander Burmaa2, Taro Kamigaki1, Hitoshi Oshitani1, Pagbajabyn Nymadawa2
Affiliation(s):
1 Department of Virology, Graduate School of Medicine, Tohoku University, Sendai, Japan
2 National Center of Communicable Diseases, Ministry of Health, Ulaanbaatar, Mongolia
Abstract:
Objectives
Influenza is an acute viral respiratory disease and usually develops mild symptoms. But sometimes it causes severe complications which may lead to hospitalizations and deaths. The disease burden of influenza is important to guide public health actions including vaccination. However it is largely unknown in developing countries including Mongolia. Mongolia is located in the mountainous plateau of East Central Asia with about 2.5 million population. Influenza causes annual epidemics in Mongolia and there is a clear seasonality of influenza observed through national influenza surveillance. All-cause mortality in 2004-2007 did not indicate particular excess mortality during influenza season, which was estimated Serfling model. Here we examined if the mortality impact of influenza is partly depending on age structure of population in Mongolia.
Materials and Methods
Age group mortality data as well as census population of Mongolia was collected between 1998 and 2007. In addition to that, monthly mortality data as well as mortality data by age group was collected from Japanese national vital statistics and age group was also collected from Japanese census for the same period. First we examine age structure of total population and mortality data between two countries and then compared the difference by age group. Next, to examine the effect of Mongolian age structure for influenza excess mortality estimates, we fitted a monthly mortality rate which was estimated from Japanese data to the age structure of Mongolian population.
Result and Discussion
The population structure of Mongolia are expansive type and most populated age group was between 15 and 29 years old (30.6%) while population of more than 70 years old was only 2.02% during study periods. In terms of number of deaths, 28.9 % of total deaths occurred among people aged above 70 years in Mongolia and 72.2% in Japan. Meanwhile Mongolian age structure with Japanese monthly mortality rate indicated a diminished seasonal component which turned out to be no excess mortality. Mongolia has a expanding population and less age proportion above 70 years old. This demographic characteristic can reduce observed mortality impact of influenza. In conclusion, expanding type age structure observed in Mongolia can be one of reasons to explain little excess mortality. As a study limitation, disease specific mortality of Mongolia did not examined in this study, which reflected mortality impact of influenza. To estimate more accurate burden of influenza in developing country, other indicators such as severe pneumonia incidence or hospitalization should be examined to estimate the disease burden of influenza clearly.
