Tuberculosis (TB), group of infectious diseases caused by the bacillus Mycobacterium tuberculosis, which kills some 3 million people every year throughout the world. TB may invade any organ but most commonly affects the respiratory system, where it has been called consumption or phthisis. In 1906 it killed 1 in every 500 persons in the United States, but today it leads to only 1 in 30,000 deaths because of effective drugs and better living conditions. Symptoms of pulmonary tuberculosis include fatigue, weight loss, persistent cough with green or yellow sputum and possibly with blood. Treatment is mainly by triple drug therapy, with streptomycin, para-aminosalicylic acid (PAS), and isoniazid, together with rest. Recovery takes about 2 years. The tuberculin skin test can show whether a person has some immunity to the disease, though the detection of the disease in its early stages, when it is readily curable, is difficult. Control of the disease is accomplished by preventive measures such as X-ray screening, vaccination, isolation of infectious people, and food sterilization.