Tuberculosis

PREVENTION

TB is largely a preventable disease, and adequate ventilation is the most important measure to prevent its transmission in the community.

In the United States, health care providers try to identify people infected with M. tuberculosis as early as possible, before they have developed active TB. They will give infected people a medicine called isoniazid (INH) to prevent active disease. This medicine is given every day for 6 to 12 months. INH can cause hepatitis (inflammation of the liver) in a small percentage of people, especially those older than 35 years.

What caused TB cases to increase the United States?

Cases of TB dropped rapidly in the 1940s and 1950s when the first effective antibiotic treatments for TB were introduced. In 1985, however, the decline ended and the number of active TB cases in the United States began to rise again. Several factors, often interrelated, were behind TB's resurgence.

• The HIV/AIDS epidemic- People with HIV are particularly vulnerable to moving from infection with M. tuberculosis to active TB and are also more likely to develop active TB when they are first infected with TB bacteria.

Some conditions appear to increase the risk that TB infection will progress to disease. The risk may be about 3 times higher (as with diabetes) to more than 100 times higher (as with HIV infection) for people who have these conditions than for those who do not. Some of these conditions are

• Infection with HIV, the virus that causes AIDS

• Injection of illicit drugs

• Recent TB infection (within the past 2 years)

Pathogenesis

When a person inhales air that contains droplets, most of the larger droplets become lodged in the upper respiratory tract (the nose and throat), where infection is unlikely to develop. However, the droplet nuclei may reach the small air sacs of the lung (the alveoli), where infection begins. The following section describes the pathogenesis of TB (the way TB infection and disease develop in the body).

TB is caused by an organism called Mycobacterium tuberculosis. M. tuberculosis organisms are sometimes called tubercle bacilli.

M. tuberculosis is a type of mycobacteria. Mycobacteria can cause a variety of diseases. Some mycobacteria are called tuberculous mycobacteria because they cause TB or diseases similar to TB. These mycobacteria are M. tuberculosis, M. bovis, and M. africanum. Other mycobacteria are called nontuberculous mycobacteria because they do not cause TB. One common type of nontuberculous mycobacteria is M. avium complex. Nontuberculous mycobacteria are NOT usually spread from person to person.

How is TB spread?

TB is spread through the air from one person to another. The bacteria are put into the air when a person with active TB disease of the lungs or throat coughs or sneezes. People nearby may breathe in these bacteria and become infected.

When a person breathes in TB bacteria, the bacteria can settle in the lungs and begin to grow. From there, they can move through the blood to other parts of the body, such as the kidney, spine, and brain.

Editor's Note:

"Race" is sometimes mentioned as a risk factor in the development of certain cancers and a number of other diseases. When you read this in a discussion about an illness, note that the explanation seldom refers to anything biological. Instead, it usually refers to behavior, such as eating habits. The kinds of behavior usually mentioned as risk factors are culturally determined. They are not genetic or biological.