A comparison of fluorescence microscopy with the Ziehl-Neelsen technique in the examination of sputum for acid-fast bacilli

SETTING: National Tuberculosis Reference Laboratory in Dakar, Senegal. OBJECTIVES: Comparison of results with fluorescence and bright-held microscopy for acid-fast bacilli. METHODOLOGY: TWO smears from 2630 consecutive sputum specimens between January 1996 and June 1998 were prepared for blinded examination of one smear each by the Ziehl-Neelsen technique and fluorescence microscopy at 1000X magnification. The time required to declare a slide as negative was determined for both techniques in a sample of 68 slides. RESULTS: Concordance was 96.9% and 92.3% for diagnostic and follow-up examinations, respectively. The yield was similar with both techniques for specimens with at least 10 bacilli per 100 fields, but higher with fluorescence microscopy in those with fewer than 10 bacilli per 100 fields. The mean time required by fluorescence microscopy before declaring a slide as negative with the same magnification was 3 minutes 34 seconds, compared to 7 minutes 44 seconds with the Ziehl-Neelsen technique. CONCLUSIONS: The results obtained with one technique are highly reproducible by the other. Fluorescence microscopy appears to be more likely to detect bacilli in paucibacillary cases than bright-field microscopy, and it more than halves the required examination time.