Symptoms may include chest pain and a prolonged cough producing sputum. About 25% of people may not have any symptoms (i.e. they remain asymptomatic). Occasionally, people may cough up blood in small amounts, and in very rare cases, the infection may erode into the pulmonary artery or a Rasmussens aneurysm, resulting in massive bleeding. Tuberculosis may become a chronic illness and cause extensive scarring in the upper lobes of the lungs. The upper lung lobes are more frequently affected by tuberculosis than the lower ones. The reason for this difference is not clear. It may be due to either better air flow, or poor lymph drainage within the upper lungs. Extrapulmonary
In 15–20% of active cases, the infection spreads outside the lungs, causing other kinds of TB. These are collectively denoted as extrapulmonary tuberculosis. Extrapulmonary TB occurs more commonly in people with a weakened immune system and young children. In those with HIV, this occurs in more than 50% of cases. Notable extrapulmonary infection sites include the pleura (in tuberculous pleurisy), the central nervous system (in tuberculous meningitis), the lymphatic system (in scrofula of the neck), the genitourinary system (in urogenital tuberculosis), and the bones and joints (in Pott disease of the spine), among others. A potentially more serious, widespread form of TB is called "disseminated tuberculosis", it is also known as miliary tuberculosis. Miliary TB currently makes up about 10% of extrapulmonary cases. Causes
Mycobacteria
The main cause of TB is Mycobacterium tuberculosis (MTB), a small, aerobic, nonmotile bacillus.
There is also not enough evidence on effectiveness of giving intermittent twice or thrice weekly short course regimen compared to daily dosing regimen in treating children with tuberculosis. Medication resistance
Primary resistance occurs when a person becomes infected with a resistant strain of TB. A person with fully susceptible MTB may develop secondary (acquired) resistance during therapy because of inadequate treatment, not taking the prescribed regimen appropriately (lack of compliance), or using low-quality medication. Drug-resistant TB is a serious public health issue in many developing countries, as its treatment is longer and requires more expensive drugs. MDR-TB is defined as resistance to the two most effective first-line TB drugs: rifampicin and isoniazid. Extensively drug-resistant TB is also resistant to three or more of the six classes of second-line drugs. Totally drug-resistant TB is resistant to all currently used drugs. It was first observed in 2003 in Italy, but not widely reported until 2012, and has also been found in Iran and India. There is some efficacy for linezolid to treat those with XDR-TB but side effects and discontinuation of medications were common. Bedaquiline is tentatively supported for use in multiple drug-resistant TB.XDR-TB is a term sometimes used to define extensively resistant TB, and constitutes one in ten cases of MDR-TB. Cases of XDR TB have been identified in more than 90% of countries.For those with known rifampicin or MDR-TB, molecular tests such as the Genotype® MTBDRsl Assay (performed on culture isolates or smear positive specimens) may be useful to detect second-line anti-tubercular drug resistance.