Tuberculosis (TB)

Tuberculosis (TB)

Tuberculosis, MTB, or TB (short for tubercle bacillus) is a common, and in many cases lethal, infectious disease caused by various strains of mycobacteria, usually Mycobacterium tuberculosis.Tuberculosis typically attacks the lungs but can also affect other parts of the body. It is spread through the air when people who have an active TB infection cough, sneeze, or otherwise transmit their saliva through the air. Most infections are asymptomatic and latent, but about one in ten latent infections eventually progresses to active disease which, if left untreated, kills more than 50% of those so infected.


Tuberculosis (TB) is a serious, re-emerging bacterial illness that usually affects the lungs.
TB bacteria are spread from person to person through the air.
There are two forms of TB: 1) TB infection, and 2) TB disease (active TB). Most people with TB have infection. People with TB infection have no symptoms and cannot spread TB to others. People with TB disease have symptoms and can spread TB to others.
People with TB infection can take medicine to keep them from getting TB disease. People with TB disease can usually be cured with anti-TB drugs. To be effective, the drugs must be taken exactly as prescribed. Some new strains of TB are resistant to many anti-TB drugs.
Preventing TB involves: 1) keeping people from becoming infected with TB, 2) keeping people with TB infection from getting TB disease, 3) treating people with TB disease, and 4) implementing precautions in institutional settings to reduce the risk of TB transmission.


What is tuberculosis (TB)?

Tuberculosis, or TB, is an infectious disease that usually affects the lungs but that can attack other parts of the body. There are two forms of TB: TB infection and TB disease (or active TB). Most people with TB have TB infection.


What is the infectious agent that causes tuberculosis?
Tuberculosis is caused by Mycobacterium tuberculosis, a bacterium.
Where is tuberculosis found?
Tuberculosis is found worldwide.
How do people get tuberculosis?
Tuberculosis is spread from person to person through the air. People with TB disease of the lung spray the bacteria into the air when they cough, sneeze, talk, or laugh. People nearby can breathe in the bacteria and become infected. To become infected, a person usually needs to be exposed for a long time to air containing many TB bacteria.

When a person breathes in TB bacteria, they lodge in the lungs and begin to multiply. From there, the bacteria sometimes move through the blood to other parts of the body, such as the kidneys, joints, and brain. In most cases, the infection is kept in check by the body's immune system. In about 10% of cases, however, the infection breaks out into active TB disease at some point during the life of the infected person.


What is the difference between TB infection and TB disease?

In most people who become infected, the body's immune system is able to fight the TB bacteria and stop them from multiplying. The bacteria are not killed, but they become inactive and are stored harmlessly in the body. This is TB infection. People with TB infection have no symptoms and cannot spread the infection to others. However, the bacteria remain alive in the body and can become active again later.

If an infected person's immune system cannot stop the bacteria from multiplying, the bacteria eventually cause symptoms of active TB, or TB disease. To spread TB to others, a person must have TB disease.

Most people who have TB infection never develop TB disease. But some infected people are more likely to develop TB disease than others. They include babies and children, persons with weak immune systems, and persons with some other kinds of lung disease. These people should take medicine to keep from developing TB disease. This is called preventive therapy.


What are the signs and symptoms of TB disease?

Symptoms of TB disease depend on where in the body the TB bacteria are multiplying. TB bacteria usually multiply in the lungs. TB in the lungs can cause:

A bad cough that lasts longer than 2 weeks
Chest pain
Coughing up blood or sputum (phlegm from deep inside the lungs)
Other symptoms are: weakness or tiredness, weight loss, chills, fever, and night sweats



How soon after exposure do tuberculosis symptoms appear?

Most persons infected with TB bacteria never develop TB disease. If TB disease does develop, it can occur 2 to 3 months after infection or years later. The chances of TB infection developing into TB disease lessen as time passes.


How is tuberculosis diagnosed?

TB infection is diagnosed by a skin test. A small needle is used to put some fluid, called tuberculin, under the skin on the inside of the arm. After 2 to 3 days, the amount of skin swelling around the test area is measured. A positive reaction usually means that the person has TB infection. TB disease is diagnosed by a chest x-ray or a test of a sputum sample.


Who is at risk for TB infection?

Anyone can get TB infection, but some groups are more likely than others to be exposed and thus get TB infection:

Persons with HIV infection or other diseases that weaken the immune system
Persons in close contact with someone who has TB disease
Homeless persons
Persons from countries were TB is common
Persons in nursing homes
Persons in prisons
Persons who inject drugs
Persons with medical conditions such as diabetes and certain types of cancer


What is the relationship between TB and HIV infection?

In many parts of the world, TB is a leading cause of death in persons with HIV infection. HIV infection weakens the immune system and makes it harder to keep the TB infection in check. Therefore, people with both TB infection and HIV infection are at very high risk of developing TB disease. All HIV-infected persons need to find out if they have TB infection. If they do, they need therapy to prevent the development of TB disease. If they have TB disease, they need anti-TB medicine.


What complications can result from tuberculosis?

Complications include chronic weakening of the lungs, damage to other organs, and death.


What is the treatment for tuberculosis?

In most cases, TB disease can be cured with anti-TB drugs. To be effective, the drugs must be taken exactly as prescribed. Treatment usually involves a combination of several different drugs. Because TB bacteria die very slowly, anti-TB drugs must be taken for 6 months or longer.

Persons with TB disease must continue to take their medicine until all the bacteria are killed, even if the symptoms of disease go away and they start to feel better. Not completing the full TB treatment can be very dangerous. The disease will last longer, the person can continue to spread the disease to others, and the rate of transmission will increase. Also, the TB bacteria can become resistant to the drugs being used to kill them.


What is multidrug-resistant tuberculosis?

Multidrug-resistant tuberculosis, or MDR TB, is TB disease caused by bacteria that are resistant to more than one anti-TB drug. MDR TB is difficult to treat and poses a major threat to the control of TB in the United States and around the world.


How common is tuberculosis?

TB infection and disease are very common worldwide. About 8 million new cases of TB disease occur each year in the world, and approximately 22,000 cases are reported each year in the United States. Also, 10 million to 15 million people in the United States are infected with TB and could develop TB disease in the future.


Is tuberculosis a re-emerging infectious disease?

Yes. With the discovery of anti-TB drugs in the 1940s, U.S. cases began to decrease for most of the 20th century. However, between 1985 and 1992, TB cases increased. This resurgence of TB prompted the mobilization of improved efforts to prevent and control TB. As a result, cases have dropped each year since 1993.


The main reasons for the increase seen between 1985 and 1992 were:

Failure to recognize TB infection and TB disease in newly arriving immigrants -- In the United States, TB occurs often in people born in areas of the world where TB is common. The numbers and proportions of TB cases in the foreign born have increased each year over the past decade and make up more than a third of reported cases.
Urban crowding and crowded group living situations -- TB cases are increasing in places where people with undiagnosed and untreated TB congregate and where health care is poor. Also, people in group settings (such as nursing homes, long-term-care hospitals, prisons, and homeless shelters) often have extended close contact with persons with TB disease. The populations in these settings are increasing, and many people in them have weak immune systems. Large outbreaks of TB have occurred in health-care facilities and prisons.
HIV infection -- The spread of HIV means that more people are at high risk for TB.
Breakdown of public health services -- When TB cases started to decrease, public policymakers concluded that TB was no longer a threat to public health. Funding was reduced, research stopped, health-care workers were not trained about TB, and services to make sure people took their medicine stopped.
Development of drug-resistant TB strains -- TB strains resistant to one or more anti-TB drugs have been allowed to evolve because of inadequate treatment programs, poor compliance with treatment, and lax public health controls.


How can tuberculosis be prevented?

High-risk persons with TB infection must complete their preventive therapy medicines.
Persons with TB disease must take all of their anti-TB medicine exactly as prescribed.
Institutions must implement precautions to reduce the risk of TB transmission.

This fact sheet is for information only and is not meant to be used for self-diagnosis or as a substitute for consultation with a health-care provider. If you have any questions about the disease described above, consult a health-care provider.