VACCINATION SITE REACTION
Read the vaccination site this way. A skin induration of 10 mm or more is
considered a reaction. Less than 10 mm induration is a nonreaction. Read the
vaccination site using a millimeter ruler and only the amount of induration, not the skin
redness. Reactions are classified in these three types: a positive reaction; a negative
reaction; and a conversion reaction.
The induration is 10 mm or more in diameter and indicates that the person has a
tuberculin infection now or has had an infection in the past. Two to eights weeks after a
person is infected with the tubercule bacillus, the skin test may provide a positive
reaction. Disadvantaged people in all countries have a higher rate of positive reactions.
Induration less than 5 mm in diameter is considered a negative reaction and
indicates that a tuberculosis infection is unlikely. A variety of factors make it possible for
the tuberculin reaction to decrease in size or even disappear even though the person
has tuberculosis. These factors include overwhelming tuberculosis, exanthematous
(eruptive) diseases, corticosteroid treatment, sarcoidosis, debility, and increased age.
Also consider that there may be something wrong with the materials used in testing. If
you suspect that the person may have tuberculosis, even though the reaction is
negative, give that test again or use another method of testing for tuberculosis.
6-10. CONVERSION REACTION
A positive reaction that has developed within a year after a negative reaction is
called a conversion reaction. This means that the skin induration has changed from a
skin induration of less than 10 mm in diameter a year ago to a skin induration greater
than 10 mm in diameter and that the increase in the size of the induration is at least 6
mm. The importance of this finding is that it indicates that the person may have had a
tuberculosis infection recently. That person will need to be checked periodically
because the possibility of developing tuberculosis is greatest during the first two years
after an infection.
6-11. GENERAL MEASURE OF CONTROL
It is more difficult to control outbreaks of respiratory infections (including
tuberculosis) than many other types of communicable diseases. In general, control
efforts are based on improving personal hygiene, avoiding contacts with patients and
carriers, controlling dust and aerial contamination, preventing overcrowding and fatigue,
and immunizing when applicable.