— As correctly pointed out by Dr Bayuk, the current overseas medical examination procedures for persons applying for immigration to the United States are designed to exclude applicants with infectious TB. According to the regulations, a person is considered to have infectious TB if the CXR is compatible with active TB and one or more sputum smear examinations is positive for acid-fast bacilli (AFB).1The decision to define infectiousness on the results of sputum smears rather than culture is based on the lower risk of transmission among persons who are AFB smear-negative1 and on at least two practical considerations. First, immigrants and refugees come from more than 100 countries, many of which do not have the laboratory capabilities to conduct mycobacterial culture. Also, drug susceptibility testing is rarely available, making it difficult to prescribe an appropriate regimen in countries with relatively high rates of drug resistance.
Cantwell MF, Onorato IM, Cauthen GM, Binkin NJ, Tipple MA. Tuberculosis Screening of Applicants for US Immigration-Reply. JAMA. 1995;273(4):287. doi:10.1001/jama.1995.03520280030029