The diagnosis of pulmonary TB is made by the demonstration of acid-fast bacilli (AFB) in sputum and the growth of M. tuberculosis in culture. These patients typically have an abnormal chest radiograph, as previously described. M. tuberculosis is a slow-growing bacterium, and cultures can take up to 6 weeks to grow. A PCR assay developed for M. tuberculosis can be run on AFB smear-positive sputum to hasten the diagnosis of pulmonary TB. A positive PCR on AFB-positive sputum is diagnostic of pulmonary TB, but a negative test does not rule out the diagnosis.

Table 16-5 Clinical Manifestations of Active Tuberculosis in Early verus Late* Human Immunodeficiency Virus Infection




Tuberculin test

Usually positive

Usually negative




Pulmonary distribution

Upper lobe

Lower and middle lobes


Often present

Typically absent

Extrapulmonary disease

10%-15% of cases

50% of cases

Modified from Murray JF. Cursed duet: HIV infection and tuberculosis. Respiration 1990;57:210-220.

"For practical purposes, "early" and "late" may be defined as CD4+ cell counts >300 cells/mm3 and <200 cells/mm3, respectively.

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