The year by which tuberculosis could be eradicated, has been discussed for several
foreign countries, and based on those results, new strategic plans and goals have been
elaborated. Therefore, in Japan too, it was desired to estimate the point at which
eradication of tuberculosis would be achieved.
The author estimated the year of eradication of tuberculosis, according to the criterion
proposed by Dr. Styblo that "tuberculosis is eradicated when the prevalence of tuberculosis
infection in the general population has fallen below 1 % and continues to decrease".
If the risk of infection is changing at a regular rate, it is possible to estimate the risk
of infection at any particular time. Once the risk of infection is determined, it is also
possible to calculate the age-specific prevalence of infection and the proportion of the
population infected with tubercle bacilli at any given time.
In Japan, the risk of infection before World War ‡U was assumed to be around 4%;
since then, it has declined on average, by 10 to 11 % annually. The incidence rate in Japan
also has declined, on average, by 10 to 11 % annually. However, since late 197Os, the annual
speed of decline of the incidence rate has slowed down. Therefore, I assumed that the recent
trend of the infection risk is the same as the trend of the recent incidence rate among the
0-29 year age-group.
The size of the effect of age on the risk of infection has been discussed. The author also
considered age-effects in the model. The weight applied to the risk of infection by age was
determined by examining the age-specific positive rates in the 1930s, that's before the era
when BCG vaccination was widely used.
Weighting the risk-difference by age to the model that the annual risk of infection up
to 1947 was 4 % constantly since then, it declined by 10 % annually from 1948 to 1977 ; and
then, declined by 5 % annually, I concluded that the eradication of tuberculosis in Japan will
be achieved around 2060.
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