Tuberculosis

A patient can test positive for TB and never be contagious — but miss the distinction between latent and active disease, and you'll isolate the wrong person or fail to isolate the right one.

Tuberculosis is caused by Mycobacterium tuberculosis, an airborne pathogen requiring airborne precautions (negative-pressure room, N95 respirator, door closed). The critical clinical divide is latent TB infection (LTBI) versus active TB disease. In LTBI, the immune system walls off the bacteria; the patient is asymptomatic, has a positive tuberculin skin test (TST) or interferon-gamma release assay (IGRA), but has a normal chest X-ray and negative sputum — they are NOT infectious and do NOT require isolation. Active TB presents with a persistent cough lasting 3+ weeks, night sweats, low-grade fever, weight loss, and hemoptysis. Diagnosis requires a positive chest X-ray plus three sputum specimens for acid-fast bacilli (AFB) collected 8–24 hours apart, with at least one early-morning specimen. Active TB is confirmed by sputum culture, which takes 2–8 weeks. First-line treatment is RIPE therapy: Rifampin, Isoniazid (INH), Pyrazinamide, and Ethambutol for 2 months, then Rifampin and INH for 4 more months. INH requires pyridoxine (vitamin B6) supplementation to prevent peripheral neuropathy. Airborne precautions continue until the patient has three consecutive negative AFB sputum smears collected on separate days.

Key Distinctions

Don't confuse a positive TST with active disease — a positive skin test only shows exposure or prior BCG vaccination, not infectiousness. Students mix up droplet and airborne precautions: TB requires an N95 respirator and negative-pressure room, not a simple surgical mask. LTBI treatment is INH alone for 9 months; active TB requires multi-drug RIPE therapy — using single-drug therapy for active disease promotes resistance.

Clinical Pearl

RIPE cleans up TB: Rifampin (orange secretions — monitor LFTs), Isoniazid (give B6 — monitor LFTs), Pyrazinamide (uric acid up — monitor LFTs), Ethambutol (eye exams). Three negative sputums = isolation off.