Objectives: The purpose of this study was to assess the effects of recent influenza epidemics on mortality in Japan.
Methods: We applied a new definition of excess mortality associated with influenza epidemics and a new estimation method (new method) proposed in our previous paper to the national vital statistics for 1975-1999 (ICD8- ICD10 had been adopted) in Japan. This new method has the advantages of removing a source of random variations in excess mortality and of being applicable to shifting trends in mortality rates from different causes of death in response to the revision of ICD. The monthly rates of death from all causes other than accidents (all causes) and some cause-specific deaths such as pneumonia, malignant neoplasm, heart disease, cerebrovascular disease (C. V. D) and diabetes (D. M.) were analyzed by total and by five age groups: 0-4 years, 5-24 years, 25-44 years, 45-64 years, and 65 years old or older.
Results: The following findings were noted:
1. For each epidemic in every other year since 1993, large-scale excess mortality of over 10, 000 deaths was observed and the effect of those epidemics could be frequently detected in mortality even among young persons, i. e., 0-4 years or 5-25 years.
2. Excess mortality associated with influenza epidemics influenced mortality by some chronic diseases such as pneumonia, heart disease, C. V. D., D. M., etc. For some epidemic years since 1978, excess mortality rates were detected even in mortality by malignant neoplasm.
Conclusions: It has been definitely shown by applying the new method to the national vital statistics for 1975-1999 in Japan that influenza epidemics in recent years exerted an influence on overall mortality, increasing the number of deaths among the elderly and the younger generation. Monitoring of the trends in excess mortality associated with influenza epidemics should be continued.
