Is Tuberculosis Contagious?
Infection and Tuberculosis
Tuberculosis is very contagious from person to person through air droplets from coughing or sneezing.
Transmission of Tuberculosis from Person to Person
Tuberculosis is considered infectious but is not transmitted from person to person.
Generally, a disease like this is caused by an infectious agent and not spread between people.
Tuberculosis, although infectious, is not a genetic disease. It is not caused by a defective or abnormal gene.
Transmission of Tuberculosis
Transmission of Tuberculosis to a person can be by way of:
Airborne droplet transmission; not clothing or bedding; not handshakes, toilet seats, food utensils or other contact; rarely from contaminated beef or milk (bovine tuberculosis).
Contagiousness properties for Tuberculosis:
Contagious by droplet?:
Contagious from food?:
Contagious by physical contact (non-sexual)?:
Contagious by handshake?:
Contagious from bedding?:
Contagious from clothing?:
Contagious from toilet seats?:
Discussion about Contagion of Tuberculosis:
Tuberculosis, NIAID Fact Sheet: NIAID (Excerpt)
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
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
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 hairlike 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.
The site of initial infection is usually the alveoli — the
balloonlike 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
Some of the bacilli may be killed immediately; others may
multiply within the macrophages. Infrequently, but especially in
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
nodules 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
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 cause
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 often 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
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, along with live immune cells, form granulomas whose
centers have the consistency of soft cheese, 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
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 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
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 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
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
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
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 and ethambutol (or
streptomycin), which are used only in the first two months of
treatment. This treatment is referred to as short-course
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 should
receive at least three drugs to which the bacteria are
TB is largely a preventable disease. In the United States,
prevention has focused on identifying infected individuals early —
especially those who run the highest risk of developing active
disease — and treating them with drugs in a program of directly
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
- People with positive tuberculin skin tests and abnormal
chest x-rays compatible with inactive TB (lesions caused by
- 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
- 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;
- Residents of long-term care facilities such as prisons,
nursing homes, and mental institutions.
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
More Effective Vaccines are
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
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, making TB the
leading cause of death in HIV-infected individuals. 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
In the United States, people coinfected with TB and HIV develop
active TB at a rate of about 8 percent each year. By
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
X-rays, sputum smears, and physical exams may also fail to
provide an indication of TB infection in HIV-infected individuals.
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.
NIAID Research Agenda for
NIAID, the lead institute for TB research at the National
Institutes of Health, supports more than 100 research projects
related to TB. In fiscal year 1999, NIAID will devote an estimated
$40 million to TB research.
NIAID has a comprehensive TB research agenda that supports the
- Studies of the epidemiology and natural history of TB.
- Basic research into the biology of TB and the host immune
response to M. tuberculosis.
- The development of new tools to diagnose TB.
- The development of new drugs or new ways to deliver standard
- Clinical trials of anti-TB therapies.
- The development of new vaccines to prevent TB.
- Training to increase the number of TB researchers.
- New ways to educate health care workers and the public about
This multi-disciplinary program draws on the Institute's
expertise in immunology and microbiology, as well as its
capabilities in drug and vaccine development honed as part of the
research effort in AIDS and other infectious
(Source: excerpt from Tuberculosis, NIAID Fact Sheet: NIAID
Tuberculosis: NWHIC (Excerpt)
TB is spread through the air from one person to another. The bacteria
are put into the air when a person with TB disease of the lungs or throat
coughs or sneezes. People nearby may breathe in these bacteria and become
infected. (Source: excerpt from Tuberculosis: NWHIC)
Tuberculosis: NWHIC (Excerpt)
Remember, TB is spread through the air. People cannot get infected with
TB bacteria through handshakes, sitting on toilet seats, or sharing dishes
and utensils with someone who has TB. (Source: excerpt from Tuberculosis: NWHIC)
About contagion and contagiousness:
Contagion and contagiousness refers to how easily
the spread of Tuberculosis is possible from one person to another.
Other words for contagion include "infection", "infectiousness",
"transmission" or "transmissability".
Contagiousness has nothing to do with genetics
or inheriting diseases from parents.
For an overview of contagion,
see Introduction to Contagion.
» Next page: Treatments for Tuberculosis
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