A 29-year-old man is admitted to the hospital with fever and

[kailash]

A 29-year-old man is admitted to the hospital with fever and cough. The symptoms began roughly 1-month prior and have been intermittent. He states that his cough is often productive of thick secretions and that, despite normal food intake, he has lost about 10 pounds in the past month. He is a volunteer at a local hospital and has received no special health care personnel vaccinations or screening tests. On examination, the patient appears somewhat thin, tired, and is coughing intermittently. His temperature is 38.0 C (100.4 F) and respirations are 16/min. He has patchy bilateral rhonchi over all lung fields. Prior to initiating therapy for this condition, the laboratory test required to confirm the suspected diagnosis is a

A. chest radiograph
B. sputum acid-fast stain
C. sputum culture
D. sputum Gram stain
E. tuberculin skin test

[kailash]

The answer is B. The patient likely has tuberculosis. Virtually all M. tuberculosis is transmitted by airborne particles that are 1 to 5 µm in diameter. The symptoms of tuberculosis are protean and nonspecific and can be classified as either systemic or organ-specific. Classic systemic symptoms include fever, night sweats, anorexia, weight loss, and weakness. However, since tuberculosis is associated with other illnesses that have similar symptoms, this lack of specificity can result in a delayed diagnosis or even a misdiagnosis. Organ-specific symptoms of pulmonary tuberculosis include cough, pleuritic pain, and hemoptysis. The requirement for diagnosis is the presence of the organism that appears by acid-fast staining in a sputum sample.

In patients with primary tuberculosis, chest radiographs (choice A) often show infiltrates in the middle or lower lung zones, with ipsilateral hilar adenopathy. These findings are non-specific and are not used for confirmation of the diagnosis.

A sputum culture (choice C) is not useful in this case since the organism responsible for TB is fastidious and is difficult to culture, and certainly does not grow rapidly.

The organism responsible for TB does not stain with traditional Gram stain dyes (choice D) and therefore requires special staining such as acid-fast in order to detect it.

Although it is imperfect, the gold standard for diagnosing latent tuberculosis infection remains the intradermal injection (choice E) of purified protein derivative (5 TU) into the volar or dorsal surface of the forearm (Mantoux method). The test has no role in the diagnosis of active infection.