Tuberculosis

TRANSMISSION

TB is primarily an airborne disease. The bacteria are spread from person to person in tiny microscopic droplets when a TB sufferer coughs, sneezes, speaks, sings, or laughs. Only people with active TB can spread the disease to others. People with TB who have been treated with the correct drugs for at least 2 weeks, however, are no longer contagious and do not spread the bacteria to others.

Classification System

Many systems have been used to classify people who have TB. The current classification system (Table 1.3) is based on the pathogenesis of TB. Many health departments and private health care providers use this system when describing patients. Thus, it is important for public health workers to be familiar with this system. In particular, public health workers should be aware that any patient with a classification of 3 or 5 should be receiving treatment for TB, and the case or suspected case should be reported.

Sites of TB Disease

TB disease can occur in different places in the body. Pulmonary TB is TB that occurs in the lungs. About 85% of TB cases are pulmonary. Most patients with pulmonary TB have a cough and an abnormal chest x-ray, and they should be considered infectious until they meet certain criteria.

Extrapulmonary TB occurs in places other than the lungs, such as the larynx, the lymph nodes, the pleura (the membrane surrounding each lung), the brain, the kidneys, or the bones and joints. Extrapulmonary TB occurs more often in people who are infected with HIV than in people who are not infected with HIV. In HIV-infected people, extrapulmonary TB is often accompanied by pulmonary TB. Most types of extrapulmonary TB are not considered infectious.

When Should You Suspect Tuberculosis (TB)?

TB is a disease caused by Mycobacterium tuberculosis. TB disease should be suspected in persons who have the following symptoms:

• Unexplained weight loss

• Loss of appetite

• Night sweats

• Fever

• Fatigue

If TB disease is in the lungs (pulmonary), symptoms may include:

• Coughing for  3 weeks

What Is It?

The Mantoux tuberculin skin test (TST) is the standard method of determining whether a person is infected with Mycobacterium tuberculosis. Reliable administration and reading of the TST requires standardization of procedures, training, supervision, and practice.

How Is the TST Administered?

The TST is performed by injecting 0.1 ml of tuberculin purified protein derivative (PPD) into the inner surface of the forearm. The injection should be made with a tuberculin syringe, with the needle bevel facing upward. The TST is an intradermal injection. When placed correctly, the injection should produce a pale elevation of the skin (a wheal) 6 to 10 mm in diameter.

QuantiFERON®-TB Gold Test

What is it?

The QuantiFERON®-TB Gold test (QFT-G) is a whole-blood test for use as an aid in diagnosing Mycobacterium tuberculosis infection, including latent tuberculosis infection (LTBI) and tuberculosis (TB) disease. This test was approved by the U.S. Food and Drug Administration (FDA) in 2005.

How does it work?