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Case 5: A 32-Year-Old with Chronic Cough

You answered:

A If a nucleic acid amplification test on sputum is positive for Mycobacterium tuberculosis, sputum culture is not required.

This answer is incorrect. A positive nucleic acid amplification test on the patient’s sputum would help make a rapid diagnosis of TB, but the evaluation of all cases of suspected TB should include a sputum culture, both to confirm the diagnosis and to perform drug susceptibility testing. Although nucleic acid amplification testing has excellent specificity for M. tuberculosis (98-99%), it has a reported sensitivity of only 40-80% on smear-negative specimens.

Choose another answer:

B If the pleural effusion is tapped, there is greater than 80% likelihood that a Ziehl-Neelsen stain of pleural fluid will show AFB.
C The patient’s small tuberculin skin test reaction is probably due to prior BCG vaccination, and an alternative diagnosis should be sought.
D Therapy for TB should be initiated while the diagnostic work-up continues.
E The patient’s CD4 cell count is almost certainly less than 100 cells/mm3.

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