The paper on prevalence of tuberculosis (TB) infection according to BCG
vaccination status by Pulickal and Fernandez is appreciated for the
focus on childhood TB infection, especially in Kerala where it had not
previously been explored(1). Several studies in other parts of India
report lack of protection of TB infection by BCG vaccination(2). The
protection reported in Kerala appears to be artifact of analysis. Using
10 mm cut-off value for PPD response in non-vaccinated and 15 mm in
vaccinated children deflates sensitivity of TB infection in the
latter(2-5). Different cut-off values is inappropriate in school-age
children in India(2-5). The recommendation is to ignore BCG status for
assessing TB infection prevalence by PPD test(2,3,5).
The analysis should have started with determining the
cut-off values appropriate for Palakkad region, by drawing superimposed
graphs of frequency distributions of reaction sizes in both groups(2,
4). Examples of this method may be found in several papers(2-5). If they
are similar, the common antimode should be used as cut-off value. If
they are dissimilar then the 2 antimodes give valid cut-off values for
comparison. Clues in the table suggest that distributions are quite
similar, as the proportions according to reaction sizes are similar.
Thus, <5 mm reaction was 60.3% and 60.2% and >9 mm was 26% and 24% in
the 2 groups, respectively(1). Neither difference is statistically
significant(1).
A re-analysis and re-interpretation are requested so
that we may know if BCG response is qualitatively better in Kerala than
in neighbouring Tamil Nadu and other States in India(2-5).
T. Jacob John,
439 Civil supplies Godown Lane,
Kamalakshipuram,Vellore, TN, 632 002, India.
E-mail:
[email protected]
1. Pulickal AS, Fernandez GVJ. Comparison of the
prevalence of tuberculosis infection in BCG vaccinated versus
non-vaccinated school age children. Indian Pediatr 2007; 44: 344-347.
2. Gopi PG, Subramani R, Nataraj T, Narayanan PR.
Impact of BCG vaccination on tuberculin surveys to estimate the annual
risk of tuberculosis infection in south India. Indian J Med Res 2006;
124; 71-76.
3. Chadha VK, Jagannatha PS, Suryanarayana HV.
Tuberculin sensitivity in BCG vaccinated children and its implication
for annual risk of infection estimation. Indian J Tuberc 2000; 47:
139-146.
4. John TJ. BCG, tuberculin surveys and annual rate
of tuberculosis infection in south India. Indian J Med Res 2007; 125:
95-98.
5. Chadha VK, Jagannatha PS, Kumar P. Tuberculin sensitivity among
children vaccinated with BCG under universal immunisation programme.
Indian J Pediatr 2004; 71: 1063-1068.
