An estimated 9 million new cases of TB occurred worldwide in 2013, with ~1.5 million TB-related deaths—almost entirely in low-income countries. Globally, TB rates are stable or falling.
- In the United States, TB primarily affects HIV-infected adults, immigrants, the elderly, and disadvantaged/marginalized populations.
- Isolates of M. tuberculosis that are multidrug-resistant (MDR; resistant to at least isoniazid and rifampin) and extensively drug-resistant (XDR; resistant to isoniazid, rifampin, and fluoroquinolones and to amikacin, kanamycin, or capreomycin) are increasing in frequency; ~480,000 cases of MDR-TB may have emerged in 2013, of which ~10% were probably XDR.
- Disease from a pt with pulmonary TB is spread by droplet nuclei that are aerosolized by coughing, sneezing, or speaking.
- - Droplets <5-10 µm in diameter may be suspended in air for several hours.
- - Transmission is determined by the intimacy and duration of contact with a pt with TB, the degree of infectiousness of the pt, and the shared environment.
- - Pts with cavitary or laryngeal disease are most infectious, with as many as 105-107 acid-fast bacilli (AFB)/mL of sputum.
- Risk factors for development of active disease after M. tuberculosis infection include recent acquisition (i.e., within the preceding 18 months), comorbidity (e.g., HIV disease, diabetes, silicosis, immunosuppression, gastrectomy), malnutrition, tobacco smoking, and presence of fibrotic lesions.