Alan D. T. Barrett

The Infectious Agent

Occurrence Globally there are nearly 9 million new TB cases and nearly 2 million TB-related deaths each year. TB occurs throughout the world, but the incidence varies greatly (see Map 5-8). In some countries in sub-Saharan Africa and Asia the annual incidence is several hundred per 100,000. Drug-resistant TB is of increasing concern. Multidrug-resistant or MDR TB is TB resistant to at least two of the most effective drugs, isoniazid and rifampin (also called first-line drugs). Extensively resistant or XDR TB is resistant to at least these two drugs and any fluoroquinolone and at least one of three injectable drugs (i.e., amikacin, kanamycin, or capreomycin). Although MDR TB occurs globally, it is less common than drug-susceptible TB. There are nearly 500,000 new cases of MDR TB each year, with some countries having proportions of MDR TB as high as 20% (see Map 5-9). MDR and XDR TB are of particular concern among HIV-infected or other immunocompromised persons.