Clinical Manual for Management of the HIV-Infected ... - myCME.com

Mycobacterium tuberculosis: Treatment in the
United States and Other High-Income Nations
Background
Tuberculosis (TB) is an infection caused by organisms
in the family Mycobacteria. These organisms grow
slowly and can be identified only with special staining
techniques, a trait that led to the name “acid-fast
bacteria.” Organisms in the Mycobacterium tuberculosis
(MTB) group cause human disease, usually a chronic
pneumonia. The destruction of MTB may produce
holes or cavities in the lung containing huge numbers
of organisms. MTB can also cause disease in other
individual organs (eg, lymph nodes, meninges, bone,
pericardium, peritoneum, intestines, urogenital tract)
and can disseminate to multiple organs, often including
the lungs, blood, liver, and spleen.
TB is almost always transmitted by persons with active
pulmonary TB who release large numbers of organisms
in their sputum. The organisms remain suspended
in the air for hours or days, making TB one of the
most easily transmitted respiratory pathogens. Most
immunologically healthy persons who are infected with
MTB do not develop active TB but remain infected
with inactive organisms (latent TB infection); only
about 10% of infected persons develop active disease
during their lifetimes. Persons with HIV infection
have much higher rates of active TB and develop active
disease at a rate approximating 10% per year.
Before the development of effective treatment, half of
all persons with TB disease died within about 5 years;
others recovered but were prone to relapse. Appropriate
application of modern chemotherapy to drugsusceptible
MTB disease cured at least 95% of persons
in the pre-HIV era.
HIV and TB cause more deaths than any other
infectious diseases worldwide, each claiming millions
of lives annually. A biologic synergy exists between
these infections: HIV-induced immunosuppression
increases susceptibility to TB infection, and active
TB infection enhances HIV replication through
immunologic stimulation. The populations infected
by these 2 pathogens overlap in many respects,
creating epidemiologic synergy. Poverty, crowded
living conditions, and inadequate efforts to reduce
transmission combine to enhance the transmission of
both organisms.
Section 6—Disease-Specific Treatment | 6–65
In the United States, most cases of TB occur among
immigrants, and TB is a relatively infrequent AIDSdefining
illness. Nevertheless, TB remains important to
HIV clinicians in the United States because it is highly
infectious yet curable with proper treatment and because
improper treatment leads to drug resistance both in
the original patient and in those to whom that patient
transmits. Although other conditions (eg, malnutrition,
diabetes, end-stage renal disease, pulmonary silicosis,
iatrogenic immunosuppression) increase the risk of TB
disease, HIV is by far the most important risk factor.
Classic pulmonary TB, with upper-lobe infiltrates
and cavitary lesions, may occur in HIV-infected
persons with relatively intact immunity. As the CD4
cell count decreases, TB is more likely to manifest
atypically in the chest (without cavitary disease, or
with lower-lobe disease, adenopathy, pleural effusions,
or interstitial or miliary infiltrates), as extrapulmonary
disease (particularly in lymph nodes, as meningitis, and
as disseminated infection), or both. Bone, joint, and
urogenital sites of TB are less commonly associated with
HIV-induced immunosuppression. Symptoms and signs
of TB in HIV-infected person therefore can vary widely.
Improper or erratic treatment may cause resistance to
TB medications. MTB resistance to a single drug may
complicate treatment, but usually does not prevent
successful treatment. Resistance to several drugs
(polydrug resistance) requires a longer course of therapy
using medications that are less potent and cause more
adverse effects, and markedly reduces the chance of
cure. Resistance to both isoniazid and rifampin is called
multidrug resistance (MDR) and makes treatment
especially difficult. It is extremely important to try to
avoid the development of drug resistance, especially
MDR. Treatment of drug-resistant TB should be
managed by experts or in consultation with experts.