[Comparative study of new method and the Kawai and Fukutomi methods for estimating excess mortality associated with influenza-epidemics, based upon national vital statistics from 1975 to 1997].
OBJECTIVE
In our previous paper, we proposed a new definition and method for estimating excess mortality associated with influenza epidemics. In this paper, we applied this new method to the national vital statistics for 1975-1997 in Japan and compared the estimates obtained with those generated with the Kawai and Fukutomi method.


METHODS
The monthly rates of death from all causes other than accidents (all-causes) and deaths attributed to pneumonia between 1975-1997 in Japan were analyzed using our new method. Epidemic periods were identified by examining the monthly rates for deaths attributable to influenza and associated excess mortality was then estimated for the 23-year period using defined criteria. Finally, the estimates obtained using the new method were compared with those obtained using the Kawai and Fukutomi method.


RESULTS
1) An increase in observed over expected mortality (i.e. excess mortality under the old definition) was detected even for months when influenza epidemics did not occur. 2) Estimates made using the Kawai and Fukutomi method were between 2,000-14,000 higher for deaths from all-causes and about 500-3,000 higher for those from pneumonia for each of the epidemic periods, compared to the relevant figures obtained using the new method. This finding provided a good indication of the methodological difference with the new method, which considers the range of random variation in seasonal mortality. Overall, the two methods differed in their estimates of which month had the highest excess monthly mortality rate for the year and which year had the highest excess annual mortality rate.


CONCLUSIONS
By comparing estimates obtained using the new method and the Kawai and Fukutomi method, we demonstrated that the former provides a more reasonable estimate of excess mortality rates, regardless of whether or not the period in question occurred during an influenza epidemic.
Takahashi
M
M
Department of Public Health, Saitama Medical School.
Tango
T
T
D004196:Disease Outbreaks; D004812:Epidemiologic Methods; D006801:Humans; D007251:Influenza, Human / Q000453:epidemiology / Q000401:mortality*; D007564:Japan / Q000453:epidemiology; D009017:Morbidity; D012621:Seasons; D013997:Time Factors; D014798:Vital Statistics