Tubercle bacilli retain pathogenicity after seven weeks chemotherapy

Guinea pig inoculation of sputum from patients on anti-tuberculous therapy shows that, in some cases, the tubercle bacilli retain their pathogenicity for seven weeks or more. It is and has been accepted in general for many years now that patients with active pulmonary tuberculosis receiving anti-tuberculous drugs become noninfectious in a relatively rapid time. Several factors have been said to contribute to this. Among these are: (i) patients on chemotherapy have a reduced cough and consequently expel fewer tubercle bacilli into the atmosphere; (ii) it has been suggested that patients receiving antituberculous drugs excrete these in the sputum droplets along with the tubercle bacilli and evaporation of the droplets causes concentrations of the anti-tuberculous drugs to increase, thereby reducing or destroying the viability of the organism; and (iii) chemotherapy rapidly reduces the number of bacilli excreted in sputum and this in itself may reduce the possibility of infection.