Public Health Microbiology
OUTLINE OF PRESENTATION
Tuberculosis is important communicable disease and is
a problem in developing countries as well as developed
It can develop in different parts of the body.
The main reservoir is the human population from which
it is mainly transferred by respiratory route.
If any part of the body is infected by Mycobacterium
tuberculosis, it sensitizes T cell which can be detected
by Mantoux test i.e. delayed type hypersensitive
reaction of tuberculin type( reaction seen after 12-48
In this test, a small amount of mycobacterial antigen in
the form of tuberculin or a purified protein derivative
(PPD) is injected intradermally, it reacts with sensitized
T cells and produce hypersensitivity reaction.
It results in local hardening at the site of injection which
is called indurations and swelling.
Redness appearing around the injected part is called
The diameter of induration is directly proportional to the
degree of sensitization.
PPD can be injected in different doses i.e. 1-5 Tuberculin
After injecting 0.1 ml of TU PPD intradermally, the
characteristic skin reaction develops fully after 48- 72
hrs. The result is interpreted as follows:
Area of induration 10 mm and more Reactive case
Area of induration 5-9 mm Intermediate
Area of induration less than 5 mm Non reactive
The test is though useful in diagnosis of tuberculosis, it
is not sufficient for interpreting the exact result. The test
should be correlated with clinical signs and symptoms,
clinical history and lab diagnosis .
Conditions like Mumps, Polio, Measles and malnutrition
of corticosteroids may give false positive result.
Select preferred site of injection , left hand forearm
dorsal surface, about 4 inches below the elbow joint
without vein using disinfectant 70 % ethanol around 5
With the help of 26 G needle , draw 0.1 ml of 5 TU
PPD without trapping any air bubbles.
Penetrate superficial layer of skin with an angle of 30°
with needle bevel pointing upwards and then inject
parallel to skin.
Pull the skin slowly with next hand and release the
solution, take out the syringe and mark the area.
Read the result after 72 hrs. Measure the diameter of
indurations and erythema using a ruler along the axis
of forearm in mm.
PPD solution should not enter the subcutaneous
Exposure to soap, water,scratching,rubbing or
touching the site of injection should be aovided.
The vial should not be vigorously shaken before
use to avoid the formation of air bubbles.