| 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,
|WANING OF BCG SCAR AND ITS IMPLICATIONS
|R Channabasavaiah, V Murali Mohan, HV Suryanarayana,
MS Krishna Murthy, & AN Shashidhara: Indian J TB 1993, 40,
It has been postulated that BCG scar disappears
in a good number of children and some of the vaccinated children
will get included in the non- vaccinated group and cause difficulty
in interpreting the results of tuberculin test. It was decided to
analyse information on BCG scar status in the younger population
of a rural community in 3 taluks of Bangalore district with an objective
to find out whether disappearance of BCG scar is dependent on the
age of the child, size of post-vaccination induration at initial
survey and tuberculin sensitivity status of children in whom BCG
scar has disappeared, in comparison with children in whom the BCG
scar has not disappeared. In all, 1095 children aged 0 to 14 years
were found with BCG scar in 119 randomly selected villages during
an epidemiological survey done in 1961 at the time of intake. Following
two groups of children were studied for disappearance of the scar.
Of them, a) 796 children who had BCG scar at the first survey, and
whose BCG scar status was available at 4th survey, b) 299 who showed
no BCG scar at first survey but were found with BCG scar at 2nd
survey and whose BCG scar status was available at 4th survey.
Of the BCG scars recorded at intake, 26.4% and
32.5% disappeared subsequently during three and a half and five
year periods respectively. The waning of BCG scars was independent
of age of the child and tuberculin sensitivity status at intake.
Tuberculin sensitivity status in children in whom scar had disappeared
was the same as that found in children in whom scar had persisted
at intake and after five years. The misclassification of children,
in whom scars have disappeared, as unvaccinated leads to a difficulty
in interpreting the results of tuberculin test done for the purpose
of computation of the Annual Risk of Infection. Further,
the extent of misclassification increases in proportion with the
increase in BCG coverage of the population. This finding justifies
the practice of identifying the demarcation level on the basis of
the distribution of tuberculin induration sizes for classifying
the infected persons in a population in each survey.
|KEY WORDS: BCG SCAR, WANING, RURAL POPULATION,
RISK OF INFECTION.