Tuberc Respir Dis.  2008 Oct;65(4):269-276.

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

• Kim HJ
• Oh SY
• Lee JB
• Park YS
• Lew WJ

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 > or =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: 0.98m2.43)]. 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.

Keyword

Tuberculosis; Tuberculin test; Infection

MeSH Terms

Child
Cicatrix
Humans
Mycobacterium bovis
Prevalence
Tuberculin
Tuberculin Test
Tuberculosis
Vaccination
Tuberculin

Figure

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  Figure 1 Distribution of tuberculin reactors with 10 mm or more response.

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