TB is caused by bacteria (Mycobacterium tuberculosis) and most often affects the lungs. TB is curable and preventable. TB spreads from person to person through the air. When a patient with pulmonary TB coughs, sneezes, spits, or even talks and sings, TB germs are exhaled into the air. A person is infected with TB by inhaling these TB germs in the air. However, only 5-15% of people infected with TB actually develop TB disease in their lifetime. If a person is also infected with HIV, he or she is much more likely to develop TB disease. When a person develops active TB disease, the symptoms (cough, fever, night sweats, weight loss etc.) may be mild for many months. This can lead to delays in seeking care, and leads to the transmission of the bacteria to others. Without adequate treatment, up to two thirds of people affected by TB die. TB mostly affects young adults in their most productive years. However, since almost all the young people in Japan have not yet been infected with TB and most elderly people over the age of 70 have TB germs in their lungs from their youth, over a half of TB patients are over 65 years old. Common symptoms of active pulmonary TB are a cough with sputum and blood at times, chest pains, weakness, weight loss, fever, and night sweats. However, elderly patients may not have these respiratory symptoms. For this reason, it can be difficult to diagnose TB in the elderly.

Sputum smear microscopy is one of the most important laboratory tests to diagnose TB. Laboratory technicians look at sputum samples under a microscope to see if TB bacteria are present. With such tests, diagnosis can be made within a day, but this test does not always detect cases of less infectious forms of TB. TB germs are also cultured in an incubator for three to eight weeks with various media. Since the late 1990s, liquid media have become more popular for culturing TB germs, with a faster incubation period (at least two to six weeks). Polymerase chain reaction (PCR) is another important method for detecting TB germs in sputum with a much more rapid turnaround time (at most one day, normally 4-5 hours). Active, drug-sensitive TB disease is treated with standard six- to nine-month courses of four or three antimicrobial drugs. The vast majority of TB cases can be cured when medicines are provided and taken properly.

Multidrug-resistant TB Standard anti-TB drugs have been used for decades, and resistance to the medicines is widespread. Disease strains that are resistant to a single anti-TB drug have been documented in every country surveyed. Multidrug-resistant tuberculosis (MDR-TB) is a form of TB caused by bacteria that do not respond to, at least, isoniazid and rifampicin, the two most powerful, first-line (or standard) anti-TB drugs. The primary cause of MDR-TB is inappropriate treatment. Inappropriate or incorrect use of anti-TB drugs, or use of poor quality medicines, can all cause drug resistance. Disease caused by resistant bacteria fails to respond to conventional, first-line treatment. MDR-TB is treatable and curable by using second-line drugs. However, second-line treatment options are limited, and recommended medicines are not always available. The extensive chemotherapy required (up to two years of treatment) is more costly and can produce severe adverse drug reactions in patients. In some countries, such as China, Russian Federation, and the Republic of the Philippines, 3 to 20% of the TB patients are MDR, while in Japan, less than 1% of the cases are MDR.