Download Tuberculosis (2) - Florida Heart CPR

1
Florida Heart CPR*
Tuberculosis
2 hours
Objectives
By the end of the course, students will be able to:
A. Define TB and understand the current status of the disease in the American
population
B. Demonstrate knowledge about how TB is transmitted and prevented
C. Understand how to treat and diagnosis TB
Tuberculosis (TB), a chronic bacterial infection, causes more deaths
worldwide than any other infectious disease. TB is spread through the air
and usually infects the lungs, although other organs are sometimes involved.
Some 1.7 billion people - one-third of the world's population - are infected
with the predominant TB organism, Mycobacterium tuberculosis.
Most people infected with M. tuberculosis never develop active TB.
However, in people with weakened immune systems, especially those
infected with the human immunodeficiency virus (HIV, the cause of AIDS),
TB organisms may overcome the body's defenses, multiply, and cause
active disease. Each year, 8 million people worldwide develop active TB and 3
million die.
TB on the Rise in the United States.
In the United States, TB has re-emerged as a serious public health problem.
In 1993, a total of 25,287 active TB cases, in all 50 states and the District of
Columbia, were reported to the Centers for Disease Control and Prevention
(CDC), an increase
of 14 percent since 1985. Thanks largely to improved public health control
measures, this number decreased to 22,860 in 1995. In addition to those with
active TB, however, an estimated 15 million people in the United States have
latent TB infections and may develop active TB at some time in their lives.
Minorities are affected disproportionately by TB: 54 percent of active TB cases
in 1995 were among African-American and Hispanic people, with an additional
17.5 percent found in
Asians. In some sectors of U.S. society, TB rates now surpass those in the
world's poorest countries. Among African-American men in New York City
aged 35 to 44, for example, 315 out of 100,000 had active TB in 1993, many
times the national
average of 9.8 cases per 100,000 people.
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Drug Resistance a Concern
With appropriate antibiotic therapy, TB usually can be cured. In recent years,
however, drug-resistant cases of TB have increased dramatically. Drug
resistance results when patients fail to take their medicine consistently for the
six to 12 months necessary to destroy all vestiges of M. tuberculosis. In some
U.S. cities, more than 50
percent of patients - often homeless people, drug addicts, and others caught
in poverty - fail to complete their prescribed course of TB therapy. One reason
for this lack of compliance is that TB patients may feel better after only two to
four weeks of
treatment and stop taking their TB drugs, some of which have unpleasant side
effects.
Resistance also may develop when patients are treated with too few drugs or
with inadequate doses. Particularly alarming is the increase in the number of
people
with multi-drug-resistant TB (MDR-TB), caused by M. tuberculosis strains
resistant to two or more drugs. Even with treatment, the death rate for MDRTB patients is 40 to 60 percent, the same as for TB patients who receive no
treatment.
For people co infected with HIV and MDR-TB, the death rate may be as high
as 80 percent. The time from diagnosis to death for some patients with MDRTB and HIV may be only months as they are sometimes left with no treatment
options.
Of all culture-positive TB cases in New York State in 1995, at least 13 percent
were resistant to one or more antibiotic drugs. This figure is similar to that
seen in an earlier national survey. At least 39 states reported drug-resistant
cases of TB in 1995. In
addition, CDC received numerous reports of outbreaks of MDR-TB in
hospitals and prisons. During these outbreaks, MDR-TB has sometimes
spread to hospital patients, health care workers, prisoners, and prison guards.
What Caused TB's Resurgence?
During the 19th century, TB claimed more lives in the United States than any
other disease. Improvements in nutrition, housing, sanitation, and medical
care in the first half of the 20th century dramatically reduced the number of
cases and deaths.
TB's decline hastened in the 1940s and 1950s with the introduction of the first
effective antibiotic therapies for TB. By 1985, the number of cases had fallen
to 22,201 in the United States, the lowest figure recorded in modern U.S.
history.
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In 1985, however, the decline ended and the number of active TB cases in the
United States began to rise again. Several forces, often interrelated, were
behind TB's resurgence: The HIV/AIDS epidemic. People with HIV are
particularly vulnerable to reactivation of latent TB infections, as well as to
disease caused by new TB infections. TB transmission occurs most frequently
in crowded environments such as hospitals, prisons, and shelters where HIVinfected individuals make up a growing proportion of the population.
Increased numbers of immigrants from countries with many cases of TB,
many of whom live in crowded housing.
Because of language and economic difficulties, many immigrants have limited
access to health care and may not receive treatment. Increased poverty,
injection drug use, and homelessness. TB transmission is rampant in crowded
shelters and prisons where people weakened by poor nutrition, drug addiction,
and alcoholism are exposed to M. tuberculosis.
People in poor health, especially those infected with HIV, also are prone to
deactivation of latent TB infections. Poor compliance with treatment
regimens, especially among disadvantaged groups. Some of these people
may remain contagious while others develop and pass on resistant strains of
M. tuberculosis that are difficult to treat. Increased numbers of residents in
long-term care facilities such as nursing homes. Immune function declines
with age, and as patients live longer, many suffer recurrences of latent
infections often acquired in early adulthood. As a result, other elderly people,
especially those with weak immune systems, become newly infected with TB.
The TB Organism
TB is caused by repeated exposure to airborne droplets contaminated with M.
tuberculosis, a rod-shaped bacterium. The TB bacterium also is known as the
tubercle bacillus. (A small fraction of cases are caused by related bacteria, M.
africanum and M. bovis.) M. tuberculosis, like other mycobacteria, has an
unusual cell wall, a waxy coat comprised of fatty molecules whose structure
and function are not well known. This cell wall appears to allow M.
tuberculosis to survive in its preferred environment: inside immune cells called
macrophages, which ordinarily degrade pathogens with enzymes. The coat of
M. tuberculosis also renders it impermeable to many common drugs.
Biologists call M. tuberculosis and other mycobacteria "acid fast" bacteria
because their fatty cell walls prevent the cells from being decolorized by acid
solutions after staining during diagnostic tests. Several factors make M.
tuberculosis a difficult organism to study in the laboratory, hampering TB
research. The bacteria
multiply very slowly, only once every 24 hours, and take a month to form a
colony. By comparison, other bacteria such as E. coli form colonies within
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eight hours. TB bacilli tend to form clumps, which makes working with them
and counting them difficult. Most daunting, M. tuberculosis, a dangerous,
airborne organism, can
be studied only in laboratories that have specialized safety equipment.
Transmission
TB is primarily an airborne disease. The disease is not likely to
be transmitted through personal items belonging to those with
TB, such as clothing, bedding, or other items they have touched.
Adequate ventilation is the most important measure to prevent the
transmission of TB.
Because most infected people expel relatively few bacilli,
transmission of TB usually occurs only after prolonged exposure
to someone with active TB. On average, people have a 50
percent chance of becoming infected with TB if they spend eight
hours a day for six months or 24 hours a day for two months
working or living with someone with active TB, researchers have estimated.
People are most likely to be contagious when their sputum
contains bacilli, when they cough frequently and when the extent
of their lung disease, as revealed by a chest x-ray, is great. TB
is spread from person to person in microscopic droplets droplet nuclei - expelled from the lungs when a TB sufferer
coughs, sneezes, speaks, sings, or laughs. Only people with
active disease are contagious.
Droplet nuclei are tiny and may remain in the air for prolonged
periods, ready to be inhaled. They are small enough to bypass
the natural defenses of upper respiratory passages, such as
hairs in the nose or the hair like cilia in the bronchial tubes.
Infection begins when the bacilli reach the tiny air sacs of the
lungs known as alveoli, where they multiply within macrophages.
People who have been treated with appropriate drugs for at
least two weeks usually are not infectious.
Infection
The site of initial infection is usually the alveoli - the balloon like
sacs at the ends of the small air passages in the lungs known as
bronchioles. In the alveoli, white blood cells called macrophages
ingest the inhaled M. tuberculosis bacilli.
Some of the bacilli may be killed immediately; others may
multiply within the macrophages. Infrequently, but especially in
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HIV-infected people and in children, the bacilli spread to other
sites in the body. This dissemination sometimes results in
life-threatening meningitis and other problems.
During the two to eight weeks after initial infection in people with
intact immune systems, macrophages present pieces of the
bacilli, displayed on their cell surfaces, to another type of white
blood cell - the T cell. When stimulated, T cells release an
elaborate array of chemical signals. Once this response, called
cell-mediated hypersensitivity, is established, a person's T cells
usually will respond to the tuberculin skin test (PPD test) and
produce a characteristic red welt.
Some of the T-cell signals produce inflammatory reactions;
other signals recruit and activate specialized cells to kill bacilli
and wall-off infected macrophages in tiny, hard grayish capsules known as
tubercles.
From then on the body's immune system maintains a standoff
with the infection, sometimes for years. In the tubercles, TB
bacilli may persist within macrophages, but further multiplication
and spread of M. tuberculosis are confined. Most people
undergo complete healing of their initial infection, and the
tubercles calcify and lose their viability. A positive TB skin test,
and in some cases a chest x-ray, may provide the only evidence of the
infection.
If, however, the body's resistance is low because of aging,
infections such as HIV, malnutrition, or other factors, the bacilli
may break out of the tubercles in the alveoli and lead to active disease.
Active Disease
On the average, people infected with M. tuberculosis have a 10
percent chance of developing active TB at some time in their
lives. The risk of developing active disease is greatest in the
first year after infection, but active disease sometimes does not
occur until many years later.
Active TB usually results from the spread of bacilli from the
alveoli through the bloodstream or lymphatic system to other
sites, usually elsewhere in the lungs or local lymph nodes. In 15
percent of cases, the bacilli cause disease in other regions,
such as the skin, kidneys, bones, or reproductive and urinary systems.
At the new sites, the body's immune defenses kill many bacilli,
but immune cells and local tissue die as well. The dead cells
and tissue form granulomas with the consistency of soft cheese,
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where the bacilli survive but do not flourish. The early symptoms
of active TB can include weight loss, fever, night sweats, and
loss of appetite, or they may be vague and go unnoticed by the affected
individual.
As more lung tissue is destroyed and the granulomas expand,
cavities in the lungs develop, and sometimes break into larger
airways called bronchi. This allows large numbers of bacilli to
spread when patients cough. As the disease progresses, the
granulomas may liquefy, perhaps as a result of enzymes
secreted by the body's own immune cells. This creates a rich
medium in which the bacilli multiply rapidly and spread, creating
further lesions and the characteristic chest pain, cough, and,
when a blood vessel is eroded, bloody sputum.
Most patients do not suffer shortness of breath until the lungs are
extensively damaged by the formation of cavities. Symptoms of
TB involving areas other than the lungs vary, depending upon the organ
affected.
Diagnosing TB
The tuberculin skin test, also known as the Mantoux test, can
identify most people infected with tubercle bacilli six to eight
weeks after initial exposure. A substance called purified protein
derivative (PPD) is injected under the skin of the forearm and
examined about 48 to 72 hours later. If a red welt forms around
the injection site, the person may have been infected with M.
tuberculosis, but doesn't necessarily have active disease. Most
people with previous exposure to TB will test positive on the
tuberculin test, as will some people exposed to related
mycobacteria. An important exception is people with severely
weakened immune systems, such as those with HIV.
If a person has a significant reaction to the tuberculin skin test,
additional methods can determine if the individual has active
TB. This is sometimes difficult because TB can mimic other
diseases, such as pneumonia, lung abscesses, tumors, and
fungal infections, or occur along with them. In making a
diagnosis, doctors rely on symptoms and other physical signs, a
person's history of exposure to TB, and x-rays that may show
evidence of TB infection, usually in the form of cavities or lesions in the lungs.
The physician also will take sputum and other samples, because
a positive bacteriologic culture of M. tuberculosis is essential to
confirm the diagnosis and determine which drugs will work
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against the strain of TB the patient carries. Because M.
tuberculosis grows very slowly, the laboratory diagnosis
requires approximately four weeks. An additional two to three
weeks usually are needed to determine the drug susceptibility of
the organism, making treatment decisions difficult.
Advances in Diagnosis
Recently, researchers supported by the National Institute of
Allergy and Infectious Diseases (NIAID) as well as other
investigators developed tests that use nucleic acid amplification
to speed the diagnosis of TB from four weeks to two days.
Another test in development uses luminescent chemicals from
the firefly to determine, in 24 to 48 hours, which drugs can kill the TB strain a
patient carries.
Treatment of Active Disease
The death rate for untreated TB patients is between 40 and 60
percent. With appropriate antibiotics, however, people with
drug-susceptible cases of TB can be cured more than 90 percent of the time.
Successful management of TB depends on close cooperation
between the patient and physicians and other health care
workers. Patient education is essential, and many doctors opt
for supervised, directly observed therapy (DOT). Treatment
usually combines the drugs isoniazid (INH) and rifampin, which
are given for at least six months, and pyrazinamide, which is
used only in the first two months of treatment. This treatment is
referred to as short-course chemotherapy. A fourth drug,
ethambutol, sometimes is added if a physician suspects that
drug-resistant organisms are present.
Therapy for MDR-TB
Treatment for MDR-TB often requires the use of a second line of
TB drugs, all of which can produce serious side effects. Therapy
for 18 months to two years may be necessary, and patients
often receive three drugs, one as an injection, after drug susceptibility testing.
Prevention
TB is largely a preventable disease. In the United States,
prevention has focused on identifying infected individuals early -
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especially those who run the highest risk of developing active
disease - and treating them with drugs in a program of directly observed
therapy.
INH prevents the disease in most people in close contact with
infected people or who are infected with the tubercle bacilli but
who do not have active TB. The drug is given daily for six to 12
months and strict patient compliance in taking medication is
essential to prevent drug-resistant strains from emerging.
Adverse reactions to INH are rare, although a small percentage
of patients, especially those older than 35, suffer INH-related
hepatitis. Rifampin for one year is recommended for close
contacts of patients with INH-resistant TB organisms.
In the United States, people with any of the following risk factors
should be considered for preventive therapy, regardless of age,
if they have not been previously treated for TB:
Close contacts of people with newly diagnosed infectious
TB; (In addition, children and adolescents who react
negatively to the PPD test, but who have been in close
contact with infectious people within the past three months
should be considered for preventive therapy. Therapy
should continue until a second skin test is done 12 weeks
after their first contact with an infectious person.)
People with positive tuberculin skin tests and abnormal
chest x-rays compatible with inactive TB (lesions caused by prior disease);
People whose skin test results have recently converted from negative to
positive;
People with positive skin test reactions who also have
special medical conditions known to increase the risk of
TB (e.g., HIV infection, diabetes mellitus) or who are on corticosteroid therapy;
HIV-positive people or those suspected to be HIV-infected
who now have, or had at any time in the past, positive skin
test reactions, but who do not have active infection; and
Injection drug users who have positive skin test reactions.
In addition, people younger than 35 in the following groups
should be considered for preventive therapy if they have positive skin test
reactions:
Foreign-born people from countries where TB is common;
People in medically underserved, low-income groups,
especially African Americans, Hispanics, and Native Americans; and
Residents of long-term care facilities such as prisons,
nursing homes, and mental institutions.
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Health care workers in frequent contact with TB patients or
involved with high-risk procedures such as those that induce
coughing should have a skin test every six months.
Hospitals and clinics caring for high-risk populations can take
precautions to prevent the spread of TB. All patients should be
taught to cover their mouths and noses when coughing or
sneezing. Ultraviolet light can be used to sterilize the air, and
negative pressure rooms and special filters are available, as
are special respirators and masks, that filter out the droplet
nuclei. Until they are no longer infectious, hospitalized TB
patients should be isolated in rooms with controlled ventilation and air flow.
More Effective Vaccines are Needed
In those parts of the world where the disease is common, a
vaccine composed of live, attenuated (weakened) mycobacteria
from cows (M. bovis, called bacillus Calmette-Guerin [BCG]) is
given to infants as part of the immunization program
recommended by the World Health Organization (WHO). In
infants, BCG prevents the spread of M. tuberculosis within the
body, but does not prevent initial infection.
In adults, the effectiveness of BCG has varied widely in
large-scale studies. In addition, positive skin test reactions
occur in people who have received BCG vaccine, thus limiting
the effectiveness of the PPD skin test to identify new infections.
As a result, BCG is not recommended for general use in the
United States. Because of BCG's limitations, more effective vaccines are
needed.
TB and HIV Infection
WHO estimates that 4.4 million people worldwide are coinfected with TB and
HIV. By the year 2000, TB will claim 1
million lives annually among the HIV-infected, WHO projects. In
the United States, an estimated 100,000 HIV-infected people
also carry M. tuberculosis, according to CDC.
TB frequently occurs early in the course of HIV infection, often
months to years before other opportunistic infections such as
Pneumocystis carinii pneumonia. TB may be the first indication
that a person is HIV-infected, and often occurs in areas outside
the lungs, particularly in the later stages of HIV disease.
In the United States, people coinfected with TB and HIV develop
active TB at a rate of about 8 percent each year. By
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comparison, otherwise healthy individuals infected with M.
tuberculosis have a 10 percent lifetime risk of developing
active TB. People with HIV also are at greater risk of having a
new infection progress directly to active disease.
MDR-TB in people coinfected with HIV appears to have a more
rapid and deadly disease course than seen in patients with
MDR-TB who are otherwise healthy.
Diagnosing TB in HIV-infected people is often difficult. These
patients frequently have conditions that produce symptoms
similar to those of TB, and may not react to the standard
tuberculin skin test because their immune systems are
suppressed. Although investigators have hypothesized that a
two-stage TB skin test might be more reliable than a
single-stage test in HIV-infected individuals, a recently
completed NIAID study found this not to be the case.
X-rays, sputum smears and physical exams may also fail to
provide an indication of TB infection in the HIV-infected. As a
consequence, doctors must often decide to begin anti-TB
therapy in HIV-infected people suspected of having active TB
while waiting for the results of cultures of sputum or other specimens.
Information provided by the NIH & NIAID,
Office of Communications
National Institute of Allergy and Infectious Diseases
National Institutes of Health
Bethesda, MD 20892
Public Health Service
U.S. Department of Health and Human Services
Florida Heart CPR*
Tuberculosis Assessment
1. ______, a chronic bacterial infection, causes more deaths worldwide than any
other infectious disease.
a. Malaria
b. Cholera
c. Tuberculosis
d. HIV/AIDS
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2. Lack of compliance in patients taking medication for TB may result from
a. Unpleasant side effects
b. Elimination of symptoms after 2-4 weeks of treatment
c. The extended length of time required for treatment
d. All of the above
3. Improvements in_____ dramatically reduced the number of deaths from TB in the
first half of the 20th century.
a. Nutrition
b. Housing
c. Sanitation
d. All of the above
4. The rod shaped bacterium, M. tuberculosis, is able to resist many medications
and survive inside macrophages due to its
a. Incredibly rapid proliferation
b. Unique DNA structure
c. Waxy cell wall made of fatty molecules
d. A and B
5. TB is primarily a(n)
a. Bloodborne disease
b. Airborne disease
c. Genetic disease
d. Idiopathic disease
6. The site of initial infection is usually the _____ - the balloon like sacs at the ends
of the small air passages in the lungs known as bronchii.
a. Loop of Henle
b. Alveoli
c. Medulla
d. Trachea
7. A substance called purified protein derivative (PPD) is injected under the skin of
the forearm and examined about 48 to 72 hours later. If a red welt forms around
the injection site, the person may have been infected with M. tuberculosis, but
doesn't necessarily have active disease. This process is known as the
a. TB vaccine
b. Tuberculin skin test
c. Viral screening
d. None of the above
8. The death rate for untreated TB patients is between 40 and 60 percent. With
appropriate antibiotics, however, people with drug-susceptible cases of TB can
be cured more than ____ percent of the time.
a. 50
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b. 75
c. 80
d. 90
9. TB is largely a _____ disease.
a. Unpreventable
b. Preventable
c. Rare
d. B and C
10. The spread of TB can be reduced with the use of
a. special respirators and masks, that filter out the droplet nuclei
b. negative pressure rooms
c. special air filters
d. all of the above
Florida Heart CPR*
Tuberculosis