| TUBERCULIN TESTING IN A PARTLY BCG VACCINATED POPULATION
|National Tuberculosis Institute, Bangalore: Indian
J TB 1992, 39, 149-58.
To obtain precise information for computing the
indices of tuberculosis situation in a community, with passage of
time, reliance has been placed on tuberculosis infection rates obtained
by carrying out tuberculin surveys. In most developing countries,
covered extensively by BCG vaccination without prior tuberculin
testing, the tuberculin test has problems of interpretation for
demarcating the infected persons from the uninfected. To overcome
the problem, therefore, the test results are analysed among persons
who do not show a BCG scar and are, thus, considered as normal population.
In this paper, an attempt is made to show that BCG vaccination not
always lead to the formation of a scar, and also that the scar resulting
from BCG vaccination may fade away with time and the person, thus,
may be wrongly included in the unvaccinated group. It has also been
found that there is greater fading of scars in the younger age groups:
in children 0-2 years of age, upto 52% of the scars faded away within
21 months of vaccination. This proportion steadily decreased to
about 8% in the 10-14 years age group.
The implication of the finding is that the demarcation line between
uninfected and infected persons may require to be shifted from survey
to survey, based on the distributions among the 'no scar' population.
Moreover, in a totally vaccinated community, the differences of
reactions may provide the answer to the problem of identifying the
newly infected persons.
|KEY WORDS: TUBERCULIN TEST, BCG SCAR, INFECTION,