Tuberculosis
1. Identification-identification requires finding the organism
Mycobacterium tuberculosis, the cause of TB. Respiratory symptoms
should prompt an exam of the sputum, first by an acid-fast smear, then
by
culture and identification of the organism. The smear results should be
available in hours. If positive, a diagnosis of TB should be assumed and
treatment started. Final confirmation requires isolation of the culture.
Radiographs of the chest are helpful in the identification.
2. Agent-TB is caused by an infectious agent known as mycobacterium
tuberculosis.
3. Occurrence-The number of TB cases had been declining by an
average of 5% per year nationally since 1953. This situation changed in
1985, when the incidence began to climb. In 1990, 25,701 TB cases were
reported to the CDC. This represented a 9.4% increase over 1989 and
was the largest for a single year since 1953. Reported cases increased
15.89% between 1985 and 1990.
Although the AIDS epidemic has caused many of the changes,
immigration, homelessness, drug abuse prison overcrowding, acts in
public health funding, and drug resistance have also contributed to a
situation that is out of control in some parts of the country. And
because
TB is contagious, the risk extends beyond the groups traditionally
considered high risk.
TB has changed from a disease of older people to one of young
adults
and children. It has also evolved from a disease that struck across all
racial and ethnic lines to one that is far more common among black and
Latino populations than whites. The age distribution of new cases also
point to a strong-but not absolute-link with AIDS. The greatest increase
has been in people 24-44, the same group most seriously affected by HIV
infection.
4. Reservoir-Only people were discussed but also animals.
5. Mode of Transmission-The agent infects the lungs by inhalation of
infected droplets formed during coughing, singing or sneezing of an
individual with the active form of the disease.
6. Incubation period-about 4-12 weeks
7. Period of communicability-As long as viable tubercle bacilli are
being
discharged in the sputum.
8. Susceptibility-The most hazardous period for development of clinical
disease is the first 6-12 months after infection. But in the case of HIV
infection, infection and development of TB symptoms is shorter than
that in HIV negative patients with TB. According to some reports, HIV
infected patients can develop primary progressive TB within a few weeks
of exposure to M. tuberculosis.
9. Resistance-TB has changed bacteriologically. Today in New York, as
many as 20% of TB patients are infected with M. tuberculosis that is
resistant to isoniazid (INH) and rifampin. TB experts believe that the
drug
resistance problem is due in part to poor compliance, which is bad among
TB patients. In addition, widespread indifference to TB during the last
two
decades meant that no new specific anti-TB drugs entered the pipeline,
monitoring for resistance lagged, and rapid diagnostic tests were not
developed.
10. Methods of control-Controlling TB is very difficult.
A. Preventive measures-TB specialist overwhelmingly prefer the
intradermal Mantoux test for screening. Candidates for screening include
HlV-positive patients, close contacts of TB patients, people from
countries
with high TB rates or medical conditions that predispose to active TB,
and
residents of long-term-care facilities. Because of the high prevalence
of
anergy among HlV-infected patients, the CDC recommends administering
companion tests for delayed-type hypersensitivity simultaneously with
the
Mantoux test.
Most TB patients are treated with INH and rifampin as outpatients
for 6
to 9 months. Much of the responsibility for detection, prevention and
treatment lies with our increasingly impacted and understaffed public
health clinics throughout the country. The private sector also shares in
an
increasing demand for treatment of cases. More than 35% of the reported
cases reported to the county health department come from sources other
than public health facilities.
Preventive therapy ordinarily consist of INH 300 mgs. daily for 6
to 12
months. Where the risk of TB is very high, such as in those who are HlV-
positive, 12 months is recommended. In all cases it is essential to rule
out
active TB before giving INH alone.
The BCG (Bacillus of Calmette and Guerin) vaccine has been used in
many parts of the world to prevent TB. Unless the BCG vaccine has been
received within the past year, a positive TB skin test result in any
person
should be considered as indicating TB infection regardless of the remote
history of a BCG vaccination. They should be assessed regarding TB
disease.
B. Control of patients, contacts and the immediate environment-Of
particular concern is the documented increase of disease in children.
When TB is under control in a community, children should rarely be
infected and essentially have no disease because they get the disease
only from undetected adult cases. This indicates that adults with
undetected TB are transmitting it to children.
Another reason TB has remained endemic is because of the dramatic
increase in the population and the changing demographics. Immigration of
large numbers of persons from countries where TB is common has
resulted in sustained numbers of new TB cases, despite the general
decline in those born in the U.S.
References
Benenson, A.S., (1990). Control of communicable disease in man (15th
ed.). Washington D.C.: American Public Health Association.
Davidson, P.T., Diferdinanando, G.T., Reichman, L.B., Snider,D.E. (May
15,1992). TB: coming soon to your town? Patient Care.
