Tuberculosis, or TB, is an infectious disease caused by the bacterium Mycobacterium tuberculosis.

The bacterium is spread through the air when someone with the disease coughs, sneezes, or speaks.

TB generally doesn’t cause symptoms immediately. Instead, it goes through three stages:

  • Primary infection
  • Latent infection
  • Active disease

In most people, TB is latent, meaning the bacteria are present in the body but are in a dormant state, neither making the person sick nor infecting others.

Tuberculosis is more likely to enter the active phase in people who have acquired the infection recently (in the past two years) and among those whose immune systems are weakened as a result of malnutrition, old age, infection with HIV, taking immunosuppressant drugs, or among patients who are on dialysis.

While there are effective treatments for tuberculosis, the disease can be fatal: According to the Centers for Disease Control and Prevention (CDC), tuberculosis kills more than a million people every year worldwide.

Who Is Affected by Tuberculosis?

As recently as the 1800s, TB (formerly known as "consumption" or "phthisis") caused more deaths in industrialized countries than any other disease.

The development in the 1940s of streptomycin, the first antibiotic to effectively cure TB, dramatically lowered the number of cases of tuberculosis seen in developed countries, including the United States.

Today, most cases of TB occur in Africa, Asia, and the Western Pacific region.

CDC statistics for TB show the following for 2013:

  • A third of the world’s population was infected with tuberculosis.
  • 9 million people worldwide became sick with tuberculosis.
  • 1.5 million people died of tuberculosis.
  • In the United States, just over 9,500 cases of tuberculosis were diagnosed.
  • Tuberculosis was the leading killer of people with HIV.

When active tuberculosis is diagnosed in the United States, it’s often in a person who has emigrated from a country with a much higher rate of TB.

Symptoms of Tuberculosis

The most common symptom of TB is a persistent cough that produces yellow or green sputum, particularly first thing in the morning.

As the disease progresses, the sputum may become streaked with blood.

Some other symptoms of tuberculosis include:

  • Intermittent fever
  • Night sweats
  • Lack of energy
  • Low appetite
  • Weight loss
  • General sense of being unwell

Treating Tuberculosis

Tuberculosis is treated with antibiotics. The most commonly used are isoniazid (Nydrazid), rifampin (Rifadin), pyrazinamide, ethambutol (Myambutol), and occasionally streptomycin.

However, many strains of tuberculosis have become resistant to these antibiotics, largely because of improper use of them or inadequate treatment.

Antituberculosis antibiotics must be taken for a long time — usually 6 months or longer — because the tuberculosis bacteria are very slow-growing. When antibiotics are stopped too early, before all of the bacteria in the body have been killed, those bacteria that remain often become resistant to the drug(s) that were being used.

The emergence of multidrug-resistant tuberculosis has become a major threat to successfully controlling the spread of TB worldwide.

Consequently, people diagnosed with TB today must take multiple antibiotics at once to make sure all of the bacteria are killed. 

Tuberculosis Vaccine

A vaccine for tuberculosis called bacille Calmette-Guerin, or BCG, is used in parts of the world with high rates of the infection to prevent serious complications such as meningitis.

BCG is rarely used in the United States, however, because some studies have shown that BCG is not very effective in preventing TB cases, and because treatment of latent TB infection with isoniazid is a more effective strategy to prevent tuberculosis.