3.4. AIDS and Opportunistic Infections: TB: An Airborne Disease
Description
This article is from the AIDS FAQ, by Dan Greening with numerous contributions by others.
3.4. AIDS and Opportunistic Infections: TB: An Airborne Disease
TB, a chronic bacterial infection, causes more deaths worldwide than
any other infectious disease. About one-third of the world's
population harbors the predominant TB organism, Mycobacterium
tuberculosis, and is at risk for developing the disease. The World
Health Organization (WHO) estimates that 4.4 million people worldwide
are coinfected with TB and HIV. WHO predicts that by the year 2000, TB
will take one million lives annually among the HIV-infected.
Because of their weakened immune systems, people with HIV are
vulnerable to reactivation of latent TB infections, as well as to new
TB infections. Transmission of this disease occurs most commonly in
crowded environments such as hospitals, prisons and shelters--where
HIV-infected individuals make up a growing proportion of the
population.
Active TB may occur early in the course of HIV infection, often months
or years before other OIs. TB most often affects the lungs, but it
also can cause disease in other parts of the body, particularly in
people with advanced HIV disease.
Of particular concern for people with AIDS is multi-drug-resistant TB
(MDR-TB). MDR-TB can occur when patients fail to take their TB
medicine for the prolonged periods necessary to destroy all TB
organisms, which then become resistant to the drugs. These resistant
organisms can be spread to other people. Even with treatment, for
individuals coinfected with HIV and MDR-TB, the death rate may be as
high as 80 percent, as opposed to 40 to 60 percent for people with
MDR-TB alone. The time from diagnosis to death may be only months for
some patients with HIV and MDR-TB, as they are sometimes left without
adequate treatment options.
The initial site of TB infection is in the balloon-like sacs at the
ends of the small air passages in the lungs. In these sacs, white
blood cells called macrophages ingest the inhaled TB organism. Some of
the organisms are killed immediately, while others remain and multiply
within the macrophages. If the organism breaks out of the sacs, TB can
become active disease. This spreading sometimes results in
life-threatening meningitis and other problems.
NIAID launched the first large U.S. study to assess TB treatment
strategies for people coinfected with HIV and TB. The study is aimed
at finding state-of-the-art treatment. NIAID is the lead institute for
TB research at the National Institutes of Health, supporting more than
50 research projects related to TB.
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