Tuberculosis bacteriology--priorities and indications in high prevalence countries: position of the technical staff of the Tuberculosis Division of the International Union Against Tuberculosis and Lung Disease.

Smear microscopy for acid-fast bacilli (AFB) remains the first priority for national tuberculosis programmes (NTPs) in high-prevalence countries. No other established technique offers the same advantages of accuracy, speed, appropriateness and accessibility. Its sensitivity may be reduced in HIV-positive cases or because of technical deficiencies, and it lacks specificity for viable bacilli in follow-up examinations. Its main problem is that it is tedious, necessitating an effective external quality assessment (EQA) system following international guidelines. Operational research is needed to optimise the staining he place of sputum concentration o define t and fluorescence microscopy, to challenge difficult and obsolete strategies and to streamline procedures. Culture is much more difficult to set up and is usually impossible to decentralise. Because of its lower yield and higher costs, its efficiency for case detection in NTPs will lag well behind that in industrialised countries. The technique should only be used as a preliminary to drug susceptibility testing (DST). DST should not be developed to the detriment of the AFB microscopy network and its EQA. It should be used mainly for monitoring drug resistance. Continuous monitoring of resistance in a representative sample of isolates from first-line failure and relapse cases may be more efficient and more accurate than periodic surveys among new cases, and can be used to identify MDR-TB, whose treatment should be standardised, because of considerable risk of error in the laboratory. A specialist service offering molecular techniques may be useful for exceptional cases, but it has no place in the routine work of NTPs.