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.
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 cast of TB should it occur.
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 (LTBI), can spread the disease.
LTBI 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.
The Turberculosis Skin Test, What is it?
The tuberculosis (TB) skin test (also known as 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 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. |