Every year World TB Day falls on March 24 th . On this date 144 years ago the German immunologist Robert Koch first demonstrated the existence of the TB bacterium. At the same time he showed how to identify it in a TB patient with active disease – through so-called ‘sputum microscopy’. Sputum microscopy actually isn’t a very reliable or sensitive diagnostic because it requires a good dollop of hawked up sputum from the patient – and in many TB cases this is really difficult t