The time of eradication of tuberculosis has been discussed for several countries, and
based on those results, a new strategic plan and goals have been elaborated. Considering
such developments, and in order to make a new tuberculosis control strategy, it is
important to determine the point at which eradication of tuberculosis would be achieved in
Japan.
Styblo proposed the two conventional definitions of eradication of tuberculosis, namely
that the incidence of smear-positive tuberculosis has fallen below 1 per million population
or that the prevalence of tuberculosis infection in the general population has faflen below 1
% and continues to decrease.
The bacteriological results of new cases have been reported since 1975 in Japan.
However, those results are still of doubtful validity and reliability. Therefore, the author
estimated the year of eradication of tuberculosis, according to the criterion that
tuberculosis is eradicated when the proportion of the population infected with tubercle
bacilli is less than 1 %.
If the risk of infection is changing at a regular rate, it is possible to estimate the risk
of infection at any time in the past and in the future. 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 various times in the past and
in the future.
In Japan, the risk of infection before World War ‡U was assumed to be around 4 % and
not to vary with calendar year. And based on the data from the prevalence surveys in
Okinawa in 1968 and 1973, the risk of infection was estimated 0.3 % in 1968 and has declined
on average, by 10 to 11 % annually. At that time, Okinawa was the only area free from
BCG vaccination in Japan.
The incidence rate in Japan also has declined, on average, by 10 % annually. However,
since late l970s, the annual speed of decline of the incidence rate has been 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.
---------------------[End of Page 1]---------------------