In practice, only pulmonary tuberculosis is infectious. The infection is spread by a coughing patient who sheds such high numbers of bacilli in the sputum that they can be demonstrated by staining of a sputum smear. This requires 10 000-100 000 bacilli per 1 ml of sputum. On the other hand, a culture of tubercle bacilli is positive at concentrations as low as 10-100 bacilli per ml. Such low concentrations carry only minimal risk of spreading the infection. The standard treatment regimen consists of rifampicin (RMP) and isoniazid (INH) for 6 months combined with pyrazinamide (PZA) during the first 2 months. Sometimes ethambutol is used as the third drug. Regular intake of the drugs is essential for treatment success.