Tuberculosis (TB) Test Information
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- Background Information for Tuberculosis (TB) Skin Test (PPD, Mantoux)
- How is TB Spread?
- What is Latent TB Infection (LTBI)?
- What is Active TB?
- The Tuberculosis (TB) Skin Test (PPD, Mantoux)
- Who Should Get the Tuberculosis (TB) Skin Test (PPD, Mantoux)?
- What Countries have a High Incidence of TB?
- What if I have been Vaccinated with BCG?
- Why are Students with Non-Immigrant Visas and who were Born or Grew Up in a Country Where TB is Prevalent Required to have Skin Testing Done?
- Who Should Not Get the Tuberculosis (TB) Skin Test (PPD, Mantoux)?
Background Information for Tuberculosis (TB)
Skin Test (PPD, Mantoux)
Worldwide, tuberculosis (TB) is the most common infectious disease. It is
estimated that approximately 1/3 of the entire world's population is
infected with the bacterium that causes TB. In the United States this
number is much lower, but those who live in close quarters, inner cities,
or work in health care settings are at higher risk.
Even though 1/3 of the world's population is infected with the bacterium that causes TB, nowhere near that number of people actually have TB. The rest have a condition known as Latent TB Infection (LTBI). This is a situation where the body's immune system is constantly fighting the bacterium and keeping it in check. A small number of bacterium survive in the body, but are not able to reproduce and cause the disease. This fight may continue for decades and the human host may win in the end. BUT, sometimes, often when the immune system is depleted from other fights, the bacterium wins, begins reproducing actively and TB the disease occurs. It is only those people who actually have TB that are sick, and it is only they who are contagious.
The TB test (also called a PPD or Mantoux, and similar to the old Tine test) is designed to find those individuals who have been exposed to, and carry the bacterium that causes TB, but are not yet sick. It is easier to prevent a case of TB in someone who has been infected, than to treat a case of TB should it occur.
The TB test is NOT a vaccine. It does not protect against TB. It is only designed to identify those individuals who carry the bacterium.
How is TB Spread?
It is spread through the air (by coughing) from person to
person. Only those people with active TB, NOT
those with Latent TB Infection, can spread the
disease.
What is Latent TB Infection (LTBI)?
In most people who breathe in TB bacteria and become infected, the
body is able to fight the bacteria to stop them form multiplying.
The bacteria become inactive, but they remain alive in the body and can
become active later. This is called Latent TB Infection (LTBI).
People with LTBI have no symptoms, are not infectious, and can
continue with work or school. They will usually have a positive skin
test and may develop active TB if not treated. Not everyone with
LTBI will develop active TB, but in some people, especially those with
weak immune systems, active TB does develop. The risk for
development of active TB is greatest in the first five years after
infection.
What is Active TB?
TB bacteria become active if the immune system can't stop them from
multiplying. The active bacteria begin to multiply in the body and
cause TB disease. Active TB usually causes symptoms such as cough,
fever, sweats, and weight loss. With this form of TB chest x-rays
are often abnormal and the disease can be spread to others.
The Tuberculosis (TB) Skin Test (PPD, Mantoux)
The tuberculosis (TB) skin test (also known as a PPD or Mantoux) is NOT a
vaccine. The TB test is only designed to help diagnose those who have been
infected with TB (most of whom are not sick and have no symptoms).
The TB test involves injecting a small amount of a protein from the bacterium under the skin on the forearm. There are no live bacteria in this injection, and it cannot cause any disease. The patient then returns in 48-72 hours to have their arm checked. If the body recognizes the protein (meaning infection with the TB bacterium has occurred), it will respond by causing a "bump" to appear around the injection site. The clinician will then measure how large this bump is. A small bump may be normal, while a larger bump almost always signifies infection - but not necessarily illness.
The only significant adverse reaction to this test is an abnormally large swelling in the forearm that may occur in those who have positive tests. This reaction is rare, and is usually treatable with cortisone type creams. On very rare occasions the reaction may lead to some of the skin dying and peeling off.
While there is no reason to suspect that the test would harm a developing fetus, pregnant women should probably postpone routine testing.
Who Should Get the Tuberculosis (TB) Skin Test (PPD, Mantoux)?
Anyone who has an elevated risk of TB from coming into contact with people
who have this disease should get tested. This includes people who:
- have any symptoms that could be compatible with TB
- are in the health fields
- spend time around potentially infectious people (e.g. work in a homeless shelter or prison)
- come from, or have travel to, parts of the world where TB is more common than in the U.S. - this would include almost all parts of Asia, South and Central America, Africa, East Europe
- have immune systems that are not properly working (e.g. AIDS, cancers).
Even those who have taken BCG (TB immunization in childhood) can safely get a PPD.
American College Health Association's immunization page provides more details.
What Countries have a High Incidence of TB?
It is easier to identify countries of low rather than high TB
incidence. Therefore, individuals should undergo TB screening if
they arrived from countries EXCEPT those on the following list: Canada,
Jamaica, Saint Kitts and Nevis, Saint Lucia, Virgin Islands, Belgium,
Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Liechtenstein,
Luxembourg, Malta, Monaco, Netherlands, Norway, San Marino, Sweden,
Switzerland, United Kingdom, American Samoa, Australia, or New Zealand.
What if I have been Vaccinated with BCG?
BCG (bacille Calmette-Guirin) is a vaccine for TB. This vaccine is
not widely used in the United States, but it is often given to infants and
small children in other countries where TB is common. BCG does not
always protect people from TB. If you were vaccinated with BCG, you
may have a positive reaction to a TB skin test. TB skin test
reactions to BCG vaccination in childhood usually returns to normal after
~5 years. Thus, a positive reaction probably means that you have Latent
TB Infection, especially if:
- you recently spent time with a person who has TB disease
- you are from an area of the world where TB disease is very common
- you spend time where TB is common (homeless shelters, drug-treatment centers, heal care clinics, jails, prisons)
Tuberculin skin testing still can be given to people who were vaccinated with BCG, and the skin-test results used to support or exclude the diagnosis of TB infection.
Center for Disease Control BCG Fact Sheet
Why are Students with Non-Immigrant Visas and who
were Born or Grew Up in a Country Where TB is Prevalent Required to have
Skin Testing Done?
In contrast to immigrants who may also have been born in a country
with a high incidence of TB, students with non-immigrant visas may not
have been tested upon arrival in the United States. While cases of
TB have decreased in the U.S. from 1992-2002, over 50% of total cases
occur in foreign-born people. Thus, U.S. residents born in high risk
parts of the world, have about 8 times the risk of contracting active TB
than those born in the U.S.
Who Should Not Get the Tuberculosis (TB) Skin
Test (PPD, Mantoux)?
The only people who should not have the skin test for TB done are those
who have had positive results in the past. Once a skin test is positive,
it usually remains so for life (despite treatment), and should not be
repeated.
While there is no reason to believe that this would harm a fetus, it is still prudent for pregnant women not to have this test done routinely.
Last Modified 02/06/2007