[Number of concentrated sputum smears needed to adequately assess infectivity of patients with pulmonary tuberculosis].

PURPOSE: Investigating the usefulness of 3rd concentrated sputum smear for assessments of infectivity of pulmonary tuberculosis patients. OBJECT AND METHOD: Retrospective study of the results of diagnostic 3 consecutive concentrated-sputum-smear (fluorochrome stain) of culture-proven pulmonary tuberculosis cases at our hospital from Jan. 2002 to Sep. 2003. RESULT: Altogether 362 cases were available for analysis, and 306 (84.0%) cases were smear-positive on 3 consecutive sputum tests. Of these cases, 26 cases (8.6% of smear-positive cases) were firstly smear-positive by the 3rd sputum. Of 278 cases that were already smear-positive at first and/or second sputum smear, 40 cases (13.2% of smear-positive cases) showed the highest smear-positive grade at 3rd sputum-smear, but only 6 cases (2.0% of smear-positive cases) had smear-positive grade higher by two-grade (+/- to more than 2+, or 1+ to 3+). CONCLUSION: From the results of this study together with literature review, sensitivity of 2 concentrated sputum-smear tests by fluorochrome stain is presumed to be same as, or better than that of 3 direct sputum-smear tests by Ziehl-Neelsen stain. We have to re-consider the number of concentrated sputum smear tests needed to assess the infectivity of pulmonary tuberculosis.