Nice Question Kamal
For those who don't knkow Montoux test (Tuberculin test) is one of the TB investigations. In the Montoux test 0.1 ml of standard purified protein derivative (PPD) is injected on the anterior surface of forearm using a 27-gauge needle. The transverse width (in mm) of the induration at the skin test site should reocrded after 48-72 hours.
A negative mantoux test does not rule out the diagnosis of tuberculosis while the positive test may be helpful in the diagnosis only, not to judge whether the TB treatment will be started or not.
Test is positive if the induration is 10 mm or more in diameter.
MT should be considered positive if > 5mm for patient with HIV and close contact of patient with active TB.
So the positivity of this test is not something especial for somalis or those visiting America, there is what is called "False Positive Mantoux Test" which the tuberculin test may be falsely positive without the disease due to infection with non-tuberculous mcobacterium, and also positive in individuals who have been infected sometime with mycobacterium tuberculosis, but does not distinguish between current disease and past infection, also in miliary TB the MT is usually positive.
Tuberculin test may be negative in the presence of infection with mycobacterium tuberculosis because of weak immunity as a result of malnutrition, Old age, Immunodeficiency states such as AIDS, corticosteroid therapy, chronic renal failure, and fulminant tuberculosis, it may be negative due to improper testing technique and this is also known as "False Negative Mantoux Test", for these reasons this test is not diagnostic but helpful especially if the infected person lives in a place where the TB is hardly seen.
The BCG also interferes with Mantoux test giving negative false results.
Other investigations you can do:
1- Chest X-ray
2- Sputum micriscopy (AFB smear)
3- Pleural fluid D/R, AFB culture
4- Pleural biopsy
5- Bronchial washing and biopsy for AFB smear and culture
6- PCR or M.tuberculosis
7- Biopsies of lymph node, liver, bone marrow