Tuberculin Skin Testing in a Elementary School in Taiwan

Chiu-Hsia Su

2007 Vol.23 NO.9

Correspondence Author: Chiu-Hsia Su


from Chinese version, pp,477-488
The two major uses of tuberculin skin test (TST) are for surveying the infection prevalence of tuberculosis (TB) the pathogen and for diagnosing the latent infection of TB the disease. In the past, however, due to worrying about possible interference in the test from BCG vaccination, we seldom made use of TST as a tool in TB-related studies here in Taiwan, especially on child TB situations. This study was initiated by an incidence close to the end of 2005 when an elementary school teacher was suddenly diagnosed, confirmed, and notified as an open type TB sufferer. To fulfill the required contact search protocol, we conducted a TST (2 TU PPD) screening project among the pupil population of the school. The findings are quite interesting. Firstly we saw that all 5 claimed “intimate” contacts – the five pupil officers of the teacher’s own class – showed positive TST reactions, and 3 out of the five (60%) had swollen masses ≧15 mm in diameter. Secondly, the first round TST screening involved almost all pupils attending the teacher’s class, or to them he was the homeroom teacher, and pupils of two other classes in the nearest vicinity of the first one, in which the percentages of having TST positive results turned out to be 56.7% (17/30), 43.8% (14/32), and 34.5% (10/29), respectively. The figures show that pupils attending the teacher’s class seemed to have a higher positive rate, but a chi-square test told us the differences were not statistically significant. Thirdly, a second round TST screening was also carried out which had 347 (21.2% of the entire pupil population excluding the aforementioned three classes) voluntary pupils completed the test, including 42 1st graders, 69 2nd graders, 44 3rd graders, 66 4th graders, 63 5th graders, and 63 6th graders, and the outcome showed their positive rates to be 26.2% (11/42), 26.1% (18/69), 36.4% (16/44), 48.5% (32/66), 42.9% (27/63), and 39.7% (25/63), respectively. In short, those data showed the lower grades had the lowest TST positive rate, but such seemly trend turned out to be not statistically meaningful according to our further analysis. When we conducted a regression analysis on the TST data of all participating pupils, the results said that sex and grade (age) were marked determinants for TST positive rate, but not TB contact history and BCG vaccination history because data of the latter two were not statistically significant. This article is a record of the TST screening effort, and hopefully it can provide some useful information for future TST applications and TB control on school grounds.
Keywords: tuberculosis (TB), Bacille Calmette-Guerin (BCG), tuberculin skin test (TST)