FOLLOW-UP SURVEY OF TUBERCULIN REACTION AMONG CHILDREN IN OKINAWA
Report II. Estimation of Infection Rate of Tuberculosis
1973 Volume 48 Issue 4 Pages 111-119
Details
1973 Volume 48 Issue 4 Pages 111-119
An attempt was made to estimate the annual infection rate of tuberculosis from theautumn of 1968 to the autumn of 1969 among children in Okinawa, using the datacollected in a follow-up survey of tuberculin reaction, the results of which were reportedpreviously.
First, several available methods for estimation were examined to determine theiradaptability to this study.
The most popular method in which all positive convertors are considered to newlyinfected appeared to be inadequate for this study.
If the estimation is to be made on population basis, the method in which the differenceof tuberculin positive rate between the two surveys on same population would bexecommended, as it is not only simple but also independent from measurement errors.However, this method is not applicable if the number of negative convertors amongexaminees exceeds that of positive convertors.
The authors then examined the new method proposed by Raj Narain et al and adoptedit considering it to be the most suitable for this study.
In this method, the examinees showing an evident increase exceeding a certain degree intheir tuberculin allergy are considered to be the newly infected.In the distribution curve of the differences in tuberculin reaction from 1st to 2ndsurvey, of those with average reactions of 10-29mm, a bulge is usually found in the tail ofthe elevated side. This bulge represents a group that showed a distinct increase in allergyand, in all probability, consists of the newly infected.
In this survey, the bulge appeared in the elevated tail of more than 17mm.
According to this method, the estimated infection rates for children in Okinawa showedreasonable values: such as 0.313% for 0-4 age group, 0.144% for 5-9 age group, 0.373%for 10-14 age group and 0.261% for 0-44 age group.
In comparing these values with those in European countries, the infection rate oftuberculosis among children in Okinawa is almost the same as those of France or Switzerland at the beginning of the 1960's.
In order to explain the reasons why the positive conversion rate should not be used asthe primary infection rate in this survey, the authors discussed the significance of positiveconversion as an index of tuberculosis infection and factors relating to the fluctuation oftuberculin reaction.
