Examination of smears for tubercle bacilli by Fluorescence Microscopy

IN underdeveloped countries, laboratory facilities for the bacteriological diagnosis of tuberculosis are at present, very limited. Cultural methods are unlikely to be used on a large scale for many years to come. It is, therefore, important to investigate the most economical method of examining smears for tubercle bacilli. Fluorescence microscopy was introduced by Hagemann (1937) and has since been described by many authors, including Tanner (1941, 1948), Lind and Shaughnessy (1941), Lempert (1944), Norman and Jelks (1945), Clegg and Foster-Carter (1946), Wilson (1952), Von Haebler and Murray (1954), and Needham (1957). The great advantage claimed for this method is that stained bacilli can be detected using a much lower magnification than with the usual Ziehl-Neelsen method. Considerable time is saved in examining smears and larger areas can be searched. The method has not been widely employed for two reasons. In the first place, the light source must be very bright and many of the optical systems described previously have only supplied sufficient light if the equipment was used in a darkened room. Secondly, some workers (Ritterhoff and Bowman, 1945; Kuster, 1939; Holm and Plum, 1943) consider that false positive results can be obtained, since some smears may contain small naturally fluorescent particles which can be confused with bacilli. Equipment for fluorescence microscopy that can be used in normal daylight has been in use at the Tuberculosis Chemotherapy Centre, Madras, for over two years. When it was first introduced, a comparison between this method and the conventional Ziehl-Neelsen method was undertaken to test their relative sensitivities, and to see whether fluorescence microscopy yielded false positive results. The results of this comparison are described