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What is tuberculosis?
Tuberculosis, often known as TB for short, is an infectious bacterial disease. About one in three people in the world is infected with the TB bacterium, Mycobacterium tuberculosis, but many people will not suffer significant symptoms of the disease. TB is most likely to cause serious illness in people with weakened immune systems. More than 95% of the cases of serious TB illness and death are found in developing countries. 
TB is a major global health concern. It has plagued humanity for thousands of years. Signs of TB infection have been found in Ancient Egyptian mummies, and the disease is known to have been common in ancient Greece and the Roman Empire. In the 20th century, effective treatments for TB, as well as a vaccine, were introduced and the incidence of TB fell dramatically. However, the TB bacterium has shown a remarkable ability to both evade the immune system and develop resistance to anti-TB medications. As a result, TB rates rose during the 1980s and 1990s.
In recent years, improved medication and treatment has seen the number of people experiencing illness and death from TB slowly dropping. However, TB is still a major public health concern, with two billion people infected with the bacteria, millions of active cases and over a million deaths each year. 
The cause of TB is the bacterium Mycobacterium tuberculosis. When an infected person sneezes or coughs, the bacteria are sprayed into the air. If any bacteria then enter your nose or mouth, you may become infected. TB usually does not pass from person to person through personal items (blankets, toothbrushes, clothes, etc.) You are much more likely to be infected by a person with active TB than by someone with latent TB.
While anyone can be infected with tuberculosis, the body's immune system normally keeps the bacteria in check. However, TB bacteria are notoriously hard to get rid of completely. The bacteria settle in the throat and lungs, where they employ a variety of immune system evasion mechanisms. This allows them to remain hidden within the body's own cells for long periods of time, forming small round bodies known as tubercles in the lung.
Of the people infected with TB bacteria, more than 90% are not ill and show no symptoms of disease.  The risk of active disease breaking out is higher in people whose immune system is weakened or less able to resist the TB bacteria. These may include:
- People with HIV infection;
- People with substance abuse problems (alcoholism, drug use);
- People with diabetes;
- Elderly people;
- Organ transplant recipients;
- People infected with TB bacteria in the past two years;
- People with a past active TB episode that was not correctly treated;
- Homeless people, and;
- Babies and young children.
Signs and symptoms
TB normally stays in an inactive, 'latent' state inside the body. In that state, the infected person will feel no symptoms. If TB becomes active, symptoms can include:
- Persistent cough lasting more than three weeks;
- Chest pain;
- Shortness of breath;
- Coughing up mucus or blood;
- Night sweats;
- Fatigue, and;
- Loss of appetite and weight loss.
The symptoms of TB are not always serious. Some people have only mild symptoms that are very hard to diagnose. These people can carry on infecting others without anyone knowing that something may be wrong.
Methods for diagnosis
Your doctor can diagnose tuberculosis using:
Types of treatment
Active TB treatment
Tuberculosis is treated with a combination of several (usually four) specific antibiotic medications. Because the bacteria are hard to eradicate, the treatment usually lasts several months. The patient usually stops being infectious to others after about two weeks of treatment.
It is very important to complete the treatment, even if the symptoms stop, because an incomplete treatment will not get rid of all the bacteria. If TB bacteria remain after treatment, the disease can return again and there is also the danger that the bacteria will develop resistance to the medications, also known as 'drug resistance'.
Drug resistance in TB
Drug-resistant TB bacteria have been appearing and spreading the world over. Multidrug-resistant TB (MDR-TB), and its even more dangerous variant, extensively drug-resistant TB (XDR-TB), are becoming global health problems. An estimated 5% of TB cases worldwide are classified as multidrug-resistant, and a tenth of them are classified as extensively drug-resistant. 
The disease caused by resistant bacteria is the same as non-resistant bacteria, but takes much longer and is harder to treat than non-resistant TB. Also, the medication needed to treat it has more side effects.
Latent TB treatment
Treatment of latent TB is not always necessary for the billions of people who have been infected with TB and do not have active disease. However, it is often recommended for some people who are at a high risk of developing active disease. The treatment of latent TB is usually easier and shorter than for active TB.
TB is usually a condition of the lungs, but the bacteria can travel from the lungs to other parts of the body and cause disease there (disseminated TB). Some of the more common organs that TB infects include:
- The kidneys;
- The bones, particularly the spine, and;
- The brain.
Treatment of disseminated TB is similar to treatment of active TB, but can sometimes take a longer time to complete.
For most healthy people infected with TB, the infection does not progress to active disease. The bacteria stay contained within the cells they inhabit and eventually die there and the person is no longer infected.
If an infected person's immune system weakens while TB bacteria are still present, they are at risk of developing active TB. Given good treatment, most people recover from TB and are free of the disease from then on.
For those people in whom TB does not respond well to treatment - whether because it is a drug-resistant strain or for other reasons - there is a significant danger of serious illness and death. TB can also become a chronic illness if the symptoms continue for a long period of time.
TB can be prevented by avoiding contact with infected people. It is spread by close contact with people, especially in crowded environments, such as hospitals, prisons or shelters.
The effects and spread of the disease can be prevented by identifying and treating infected people quickly. It is also important for infected people to take care not to infect others by coughing or sneezing near other people, staying away from crowded environments and sleeping in a separate room.
In most developed countries, isolation procedures and infection control measures are strictly implemented in hospitals for patients with potentially contagious active TB. Isolation is not usually required for people with latent disease.
The TB vaccine (Bacillus Calmette-Guérin vaccine) is given to people at risk, or in countries where TB is common, and can help prevent disease in children. However, it is not very effective in preventing infection in adults.