Exposure to tuberculous infection
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.