Tuberculosis

Basics

Tuberculosis (TB) is an infectious disease with protean manifestations, causing significant global morbidity and mortality

Mechanism

Infectious droplet nuclei are inhaled through the respiratory tract
Bacteria are dispersed through coughing, sneezing, speaking, and singing
Primary TB/latent TB infection (LTBI):
- Initial infection occurs when organisms enter the alveoli, become engulfed by macrophages, and spread via regional lymph nodes to the bloodstream
- Patients are usually asymptomatic
- May be progressive/fatal in immunocompromised hosts
- Positive reaction to purified protein derivative (PPD) indicates past exposure or infection
- Negative PPD does not rule out active TB
- May progress to active TB (5–10%)
Reactivation TB:
- LTBI becomes active TB
- Systemic (15%) and pulmonary (85%) symptoms
TB has an incidence of 2.9 cases per 100,000 in the U.S.
2016 had the lowest number of reported new cases
Out of the approximately 9,200 new cases reported, 67% were foreign born and 86% were HIV positive
TB is the leading cause of death in those with HIV worldwide
Still an estimated 10–15 million people are infected in the U.S. alone

Infection with Mycobacterium tuberculosis, a slow-growing, aerobic, acid-fast bacillus resulting in disease
Humans are the only known reservoir
Recent TB epidemics:
- HIV-infected patients
- Multidrug-resistant TB (MDR-TB)
- Extensively drug-resistant TB (XDR-TB):
  - High mortality, few effective drugs

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