Diagnosis

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

Sign

Early

Late

Tuberculin test

Usually positive

Usually negative

Adenopathy

Unusual

Common

Pulmonary distribution

Upper lobe

Lower and middle lobes

Cavitation

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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