TB is spread through the air from one person to another. The TB bacteria are put into the air when a person with TB disease of the lungs or throat coughs, sneezes, speaks, or sings. People nearby may breathe in these bacteria and become infected.
TB bacteria can live in the body without making you sick. This is called latent TB infection. In most people who breathe in TB bacteria and become infected, the body is able to fight the bacteria to stop them from growing. People with latent TB infection do not feel sick and do not have any symptoms. People with latent TB infection are not infectious and cannot spread TB bacteria to others.
Tuberculosis was once rare in developed countries, but the number of TB cases began increasing in 1985. Part of the increase was caused by the emergence of HIV, the virus that causes AIDS. HIV weakens a person's immune system so it can't fight the TB germs.
Many strains of tuberculosis can resist the effects of the drugs most commonly used to treat the disease. People who have active tuberculosis must take several different types of medications together for many months to eradicate the infection and prevent development of antibiotic resistance.
TB disease can be treated by taking several drugs for 6 to 9 months. There are 10 drugs currently approved by the U.S. Food and Drug Administration (FDA) for treating TB. Of the approved drugs, the first-line anti-TB agents that form the core of treatment regimens include: isoniazid (INH), rifampin (RIF), ethambutol (EMB), pyrazinamide (PZA).
About one-third of the world’s population is currently infected with TB, with one new infection occurring every second. Not all infected people are sick with active TB; in fact, 90 percent have “walled off” the bacteria within their lungs and are not ill. But the other 10 percent will develop active, contagious tuberculosis each year, and each person who develops active TB will likely infect at least 10 to 15 other people before he is treated.
About 33 million people worldwide are infected with HIV, the virus that causes AIDS. HIV/AIDS strikes the immune system, leaving it too weak to defend the body against many illnesses and invaders, including tuberculosis infection. About one-third of those with HIV also have tuberculosis, and half of those people will die from it.
Without treatment, mortality rates are high. In studies of the natural history of the disease among sputum spear-positive and HIV-negative cases of pulmonary TB, around 70% died within 10 years; among culture-positive (but smear-negative) cases, 20% died within 10 years.
In 1993, the World Health Organization (WHO) declared TB a global public health emergency, at a time when an estimated 7-8 million cases and 1.3-1.6 million deaths occurred each year. In 2010, there were an estimated 8.5-9.2 million cases and 1.2-1.5 million deaths (including deaths from TB among HIV-positive people). TB is the second leading cause of death from an infectious disease worldwide (after HIV, which caused an estimated 1.8 million deaths in 2008).
Early symptoms of active TB can include weight loss, fever, night sweats, and loss of appetite. Symptoms may be vague, however, and go unnoticed by the affected person. For some, the disease either goes into remission (halts) or becomes chronic and more debilitating with cough, chest pain, and bloody sputum (saliva).