Pulmonary tuberculosis
Alternative names:
TB; tuberculosis - pulmonary
Definition:
A contagious bacterial infection caused by Mycobacterium
tuberculosis (TB). The lungs are primarily involved, but the
infection can spread to other organs.
Causes, incidence, and risk factors:
Tuberculosis can develop after inhaling droplets sprayed
into the air from a cough
or sneeze by someone infected with Mycobacterium tuberculosis.
The disease is characterized by the development of granulomas
(granular tumors) in the infected tissues. The usual site
of the disease is the lungs, but other organs may be involved.
Primary infection is usually asymptomatic.
In the U.S., 95% of people will recover from primary TB infection
without further evidence of the disease.
Pulmonary TB develops in the minority of people whose immune
systems do not successfully destroy the primary infection.
The disease may occur within weeks after the primary infection
or it may lie dormant for years before causing disease. Infants,
the elderly, and individuals who are immunocompromised (for
example, those with AIDS,
those undergoing chemotherapy,
or transplant recipients taking antirejection medications)
are at higher risk for rapid progression to disease. In pulmonary
TB, the extent of the disease can vary from minimal to massive
involvement, but without effective therapy, the disease becomes
progressive.
The risk of contracting TB increases with the frequency of
contact with people who have the disease, and with crowded
or unsanitary living conditions and poor nutrition. An increased
incidence of TB has been
seen recently in the US. Factors that may contribute to the
increase in tuberculous infection are:
- Increase in HIV infection.
- Increasing number of homeless individuals (poor environment
and poor nutrition).
- the appearance of drug-resistant strains of TB.
Incomplete treatment of TB infections (such as failure to
take medications for the prescribed length of time) can contribute
to the proliferation
of drug-resistant strains of bacteria. Individuals with damaged
immune systems from AIDS have a higher risk of developing
active tuberculosis upon exposure to the organism. In addition,
without the aid of an active immune system treatment is more
difficult and the disease more resistant to therapy.
The incidence of pulmonary tuberculosis is 3 out of 10,000
people and increasing. In 1998, 18,361 cases of active tuberculosis
were reported to the U.S. Centers for Disease Control.
Also see:
Updated Date: 02/09/00
Updated By:J. Gordon Lambert, MD, Associate Medical Director,
Utah Health Informatics and adam.com
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