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Kim, Oh, Lee, Park, and Lew: Tuberculin Survey to Estimate the Prevalence of Tuberculosis Infection of the Elementary Schoolchildren under High BCG Vaccination Coverage
Original Article
Tuberculosis and Respiratory Diseases

Tuberculosis and Respiratory Diseases 2008; 65(4): 269-276.

Published online: 30 October 2008

DOI: https://doi.org/10.4046/trd.2008.65.4.269

Tuberculin Survey to Estimate the Prevalence of Tuberculosis Infection of the Elementary Schoolchildren under High BCG Vaccination Coverage

Hee Jin Kim, M.D.1, Soo Yeon Oh, R.N.1, Jin Bum Lee, R.N.1, Yun Sung Park2, Woo Jin Lew, M.D.1

1Korean Institute of Tuberculosis, The Korean National Tuberculosis Association, Seoul, Korea.

2Division of HIV & Tuberculosis Control, Korea Centers for Disease Control and Prevention, Seoul, Korea.

Address for correspondence: Woo Jin Lew, M.D. Korean Institute of Tuberculosis, 14, Wumyeon-dong, Seocho-gu, Seoul 157-900, Korea. Phone: 82-2-572-0709, Fax: 82-2-576-1914, wjlew@hanmail.net

Received 18 August 2008       Accepted 3 September 2008

Copyright © 2008 The Korean Academy of Tuberculosis and Respiratory Diseases

Abstract

Background

Although the prevalence of tuberculosis infections (PTBI) is one of the basic epidemiologic indices, no survey has been carried out since 1995 because the nation-wide tuberculosis prevalence survey was changed to a surveillance system. Subjects without a BCG scar are examined in a tuberculin survey. However, it is very difficult to select these subjects under high vaccination coverage. It is important to evaluate the impact of BCG vaccinations on the tuberculin response and estimate the PTBI regardless of the BCG vaccination status.

Methods

A nation-wide, school-based cross-sectional tuberculin survey was carried out among first graders in elementary school in 2006. A total of 5,148 children in 40 schools were selected by quota sampling. Tuberculin testing with 0.1 ml of two tuberculin units of PPD RT23 was carried out on 4,018 children. The maximum transverse diameter of induration was measured 48 to 72 hours later. The presence of a BCG scar was checked separately.

Results

There were no BCG scars in 6.3% of the subjects. The mean induration size of tuberculin testing was 3.7±4.4 mm, which included 1,882 (46.8%) subjects with an induration size of 0 mm. The PTBI was 10.9% (439 subjects) using a cut-off point of ≥10 mm (conventional method). The annual risk of tuberculosis infections (ARTI) was 1.9% when the mean age of the subjects was assumed to be 6 years. There was no difference in the PTBI according to the presence or absence of a BCG scar [11.2% vs 7.6% (OR: 1.54, 95% CI: 0.98~2.43)]. Using a mirror image technique with 16 mm as the cut-off point, the PTBI and ARTI had decreased to 2.4% and 0.4% respectively.

Conclusion

PTBI and ARTI, as estimated by conventional methods, appear to be high among BCG vaccinated children. A mirror image technique is more suitable for estimating the indices in a country with an intermediate burden of tuberculosis than the conventional method.

Keywords: Tuberculosis, Tuberculin test, Infection

Figures and Tables

Figure 1
Distribution of tuberculin reactors with 10 mm or more response.
trd-65-269-g001
Table 1
General characteristics of the subjects
trd-65-269-i001

*( ): column rate.

Table 2
Distribution of tuberculin reaction
trd-65-269-i002

*( ): row rate.

Table 3
Estimation of Infection Rate & Annual Risk of Infection at a mean age of 6 years old (%)
trd-65-269-i003

*Annual risk of tuberculosis infection.

Notes

This study was supported by International Tuberculosis Research Center (ITRC) Grant.

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