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Mycobacterium tuberculosis

SHEFF, BARBARA RN, CPH, HNC, MT(ASCP), MA

MICROBE OF THE MONTH
Free

Mycobacterium tuberculosis

Barbara Sheff is a microbiology consultant in Boston, Mass.

This department offers key clinical points about a particular microbe. Because of space constraints, it's not comprehensive.

Type of microbe: acid-fast, rod-shaped bacteria

Diseases caused: Airborne droplets from an infected person usually transmit Mycobacterium tuberculosis, causing tuberculosis (TB). Bacteria settle in the lungs, where they're ingested by macrophages and carried to the lymph nodes and possibly other organs and tissues. Depending on immune-system function, bacteria either become inactive (latent TB) or active (TB disease).

Signs and symptoms: A person with latent TB has no signs or symptoms, but he can develop TB disease if he's not treated. A patient in the early stage of TB disease may be asymptomatic or have nonspecific symptoms, such as anorexia, fatigue, weight loss, low-grade fever, night sweats, chest pain, shortness of breath, fever, and a productive cough with occasional hemoptysis.

Diagnosis: Collect a deeply expectorated sputum sample from the patient as soon as he awakes on three consecutive mornings. Send the samples for culture and an acid-fast bacilli (AFB) smear. Nucleic acid amplification tests can identify species of bacteria in 3 hours. Skin testing with a purified protein derivative can detect whether the patient's had contact with the bacterium, but it can't detect active infection. A chest X-ray, computed tomography, and magnetic resonance imaging can reveal characteristic cavitations in the lungs. A patient with X-ray abnormalities may undergo a bronchoscopy to obtain a tissue specimen for an AFB smear and mycobacterial culture.

Treatment: A patient with TB disease receives isoniazid, rifampin, and pyrazinamide for 2 months, followed by 4 months of isoniazid and rifampin. Ethambutol or streptomycin may be used during the first 2 months or until drug susceptibility results become available.

Nursing interventions: Place a patient with active or suspected TB disease in a negative-pressure room with respiratory airborne isolation and use standard precautions. He should remain in isolation until three consecutive sputum cultures have tested negative. Notify your infection control practitioner of suspected and confirmed TB cases.

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© 2003 Lippincott Williams & Wilkins, Inc.