About the Disease Tuberculosis TB is a contagious disease caused by mycobacterium tuberculosis When this bacillus is stained with carbol fuchsin it appears purplish red The bacterium retains this dye even when it is washed with acid and alcohol That is why it is called acid fast bacillus AFB Mycobacterium tuberculosis can remain dormant for many years in the lung without producing disease The spread of infection The patient with pulmonary TB is the source of infection to others around him especially when his sputum contains AFB When such a patient coughs he expels thousands of tiny droplets around him which have AFB in them Transmission of infection takes place when those around him breathe this contaminated air Direct sunlight rapidly destroys AFB but they can survive for long periods in darkness Thus the risk of transmission of infection is highest in those persons who stay indoors with such a patient for long periods e g family contacts The infection is largely spread in the community by patients whose sputum smear is positive for AFB The chances of a sputum smear negative patient spreading infection are much less and by those with extrapulmonary TB even lower The onset of disease 90 percent of the infected adults never develop TB They remain asymptomatic but Mantoux positive throughout their liver The rate of progression of infection to disease is highest shortly after exposure to infection and it diminishes progressively as time passes However at anytime weakening of immune responses and stress may cause multiplication and spread of the already present bacteria resulting in the onset of tuberculous disease Making a Diagnosis Cough chest pain and fever are symptoms common to a variety of lung diseases Most acute respiratory conditions subside within 3-4 weeks When these symptoms persist for more than 3 weeks or if the patient has haemoptysis a diagnosis of pulmonary TB must be considered in view of t