Examination of smears for tubercle bacilli by fluorescence microscopy.

Abstract

IN underdeveloped countries, laboratory facilities for the bacteriological
\ndiagnosis of tuberculosis are at present, very limited. Cultural methods are
\nunlikely to be used on a large scale for many years to come. It is, therefore, important to
\ninvestigate the most economical method of examining smears for
\ntubercle bacilli. Fluorescence microscopy was introduced by Hagemann (1937)
\nand has since been described by many authors, including Tanner (1941, 1948), Lind
\nand Shaughnessy (1941), Lempert (1944), Norman and Jelks (1945), Clegg and
\nFoster-Carter (1946), Wilson (1952), Von Haebler and Murray (1954), and Needham
\n(1957). The great advantage claimed for this method is that stained bacilli can be
\ndetected using a much lower magnification than with the usual Ziehl-Neelsen
\nmethod. Considerable time is saved in examining smears and larger areas can be
\nsearched. The method has not been widely employed for two reasons. In the
\nfirst place, the light source must be very bright and many of the optical systems
\ndescribed previously have only supplied sufficient light if the equipment was used in
\na darkened room. Secondly, some workers (Ritterhoff and Bowman, 1945; Kuster,
\n1939; Holm and Plum, 1943) consider that false positive results can be obtained,
\nsince some smears may contain small naturally fluorescent particles which can be
\nconfused with bacilli.
\nEquipment for fluorescence microscopy that can be used in normal daylight
\nhas been in use at the Tuberculosis Chemotherapy Centre, Madras, for over two
\nyears. When it was first introduced, a comparison between this method and the
\nconventional Ziehl-Neelsen method was undertaken to test their relative sensitivities,
\nand to see whether fluorescence microscopy yielded false positive results.
\nThe results of this comparison are described.