Tuberculosis

What is tuberculosis?

Tuberculosis (TB) is a disease caused by bacteria called Mycobacterium tuberculosis. Although this type of bacteria usually attacks the lungs, other parts of the body can also be affected such as the lymph nodes, kidneys, bones, joints, skin and genitourinary system. The extent of disease varies widely and without effective therapy, the disease can progress.

Initial infection is often asymptomatic and in most infected people, the body’s immune system is able to fight the bacteria to keep them from growing. In these cases, a latent infection is established in which the bacteria are inactive but may be reactivated to cause TB disease. In people who cannot fight off the infection—such as very young children, the elderly and anyone with compromised immune systems—the bacteria can grow and become active. This causes the initial infection to progress to established disease in the lungs and possibly in other parts of the body as well, such as the membrane lining of the brain and spinal cord. Moreover, the infection can be reactivated after years of dormancy.

How many people get tuberculosis?

The global epidemic of tuberculosis is growing and presents a significant public health concern. In fact, the World Health Organization (WHO) declared tuberculosis a global emergency in 1993. Every year, roughly 8 million people worldwide develop active TB and 3 million die. Furthermore, the WHO estimates that between 2000 and 2020, nearly 1 billion people will be newly infected, 200 million will get sick, and 35 million will die from TB.

In the 19^th century, tuberculosis was a leading cause of death in the United States. However, tuberculosis cases and deaths declined during the first half of the 20th century, at least in part due to improvements in medical care, sanitation, housing and nutrition. In addition, first generation antituberculosis drugs, discovered in the 1940s, resulted in reasonable control of the disease up until the 1980s in many countries. Recently, an increased incidence of tuberculosis has been observed in industrialized countries. This rise has been attributed partially to the deterioration of the health care infrastructure, increasing numbers of HIV infection/AIDS cases, immigration from countries where tuberculosis is common, and the emergence of drug-resistant strains of the bacteria.

How is tuberculosis spread?

Tuberculosis is spread from one person to another through 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. People with TB disease are most likely to spread it to people they spend time with every day, such as family members, friends and coworkers.

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. Tuberculosis in the lungs or throat can be infectious, meaning that it can spread to other people. However, tuberculosis in other parts of the body, such as the kidney or spine, is usually not infectious.

How is tuberculosis diagnosed?

Latent tuberculosis infection can be detected with a TB skin test, which can be obtained at the health department or a doctor’s office. The test involves injecting a small amount of testing fluid (called tuberculin) just under the skin on the lower part of the arm. After two or three days, the reaction to the testing fluid will be measured. If there is a small bump where the tuberculin was injected, it will be measured to find out if the test reaction is positive or negative. A positive reaction usually indicates a latent TB infection.

It is a good idea to be tested for tuberculosis if you:

• Have spent time with a person with known—or suspected—TB disease
• Have HIV infection or another condition that increases risk for TB disease
• Think you might have TB disease
• Are from a country where TB disease is very common, such as most countries in Latin America and the Caribbean, Africa, Asia, Eastern Europe, and Russia
• Are an intravenous drug user
• Live somewhere in the United States where TB disease is more common, such as homeless shelters, migrant farm camps, prisons and some nursing homes
• If the reaction to the skin test is positive, other tests will be conducted to see if TB disease is present, such as chest X-ray, phlegm analysis, and blood and urine tests.

How is tuberculosis treated?

Tuberculosis treatment regimens include at least four drugs (isoniazid, rifampin, pyrazinamide and either ethambutol or streptomycin) and typically last for more than six months. Treatment of drug-sensitive tuberculosis is highly effective if administered and taken properly. However, current treatment regimens are expensive, require many months, and compliance is difficult to maintain.

Can tuberculosis be prevented?

In both human and economic terms, the prevention of tuberculosis is preferable to treatment, which highlights the importance of developing of a safe and effective vaccine. The Bacillus Camille Guerin vaccine is useful in preventing certain types of tuberculosis, although its efficacy is variable. No vaccine yet exists that is truly effective against adult forms of the disease. Therefore, it will be important to identify the immune mechanisms and antigens necessary to protect against tuberculosis infection to make a significant, worldwide impact on the disease.

Below are additional resources that may be helpful to you.