TB; tuberculosis - pulmonary
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
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
numbers of AIDS cases
number of homeless individuals (poor environment and
appearance of drug-resistant strains of TB
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 almost
universally develop 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. For the year July 1993 to July
1994 there were 11,694 cases of active tuberculosis reported
to the U.S. Centers for Disease control.
tuberculosis (affects the whole body)
Routine skin testing for tuberculosis is done during routine
well-baby exams. Infants are normally screened at 1 year
and children at 5 years. Individuals exposed to tuberculosis
should be skin tested immediately and the skin test repeated
in 3 to 6 months if the initial skin test is negative.
Detection of early cases and prompt treatment are paramount
in controlling the spread of tuberculosis.
A BCG vaccination for tuberculin-negative people who have
been exposed to TB is given in some situations, but its
effectiveness is under dispute. BCG is routinely used in
some countries in Europe but is not routinely used in the
United States. People who have had BCG should not be skin
tested for tuberculosis.
not apparent, or limited to minor cough and mild
fever and night sweats
symptoms that may be associated with this disease:
of the fingers or toes
Examination of the lungs by stethoscope (auscultation)
Tests often include:
The goal of treatment is to cure the infection with antitubercular
drugs. Daily oral doses of rifampin, isoniazid, and pyrazinamide
(or occasionally others) are continued for 1 year. For atypical
tuberculosis infections, or drug-resistant strains, other
drugs may be indicated to treat the infection. Treatment
of tuberculosis is often accomplished with multiple medications.
Hospitalization is indicated to prevent the spread of the
disease to others until the infectious period is over, usually
2 to 4 weeks after the start of therapy. Normal activity
can be continued after the infectious period.
Rest, a healthy environment (clean dry air), stress
reduction and a good diet high in vitamin C, factors
normally considered conducive to good health, improve the
speed and response to treatment.
The stress of illness can often be helped by joining a support
group where members share common experiences and problems.
Symptoms may improve in 2 to 3 weeks, with improvement seen
in the chest X-ray lagging behind clinical improvement.
All medications used to treat TB have some toxicity. Rifampin
and isoniazid may both cause a noninfectious hepatitis.
Rifampin may also cause an orange or brown coloration of
tears and urine.
Other complications include drug resistance to particular
TB strains and a relapse of the disease in some patients.
Calling your health
Call your health care provider if you have been exposed
to tuberculosis, or if symptoms of TB develop.
Call your health care provider if symptoms persist despite
Also call if new symptoms develop, including indications
that complications are developing.