喀痰における抗酸菌塗抹陽性培養陰性

抗酸菌検出における諸問題に関連して

抄録

It is estimated that the number of sputum smear-positive and culture-negative cases (SPCN) has recently been increasing in Japan.
Although this phenomenon has been well known since the early stage of tuberculosis chemotherapy era, its clinical significance is as yet not so clear
From the review of literatures and based on the author's own experiences, it may be summarized as follows:
Some of this phenomenon are caused by technical errors during the procedure of staining or microscopical examination.
The routine culture method widely employed at present is reliable enough for clinical purpose, if it is performed very carefully; for example, the immediate inoculation after alkali treatment, reduced inoculum size and stable temperature during incubation.
The incubation period of all SPCN specimens should be extended up to sixteen weeks.
The SPCN cases found during the course of primary chemotherapy with intensive regimens are regarded as a normal step prior to negative conversion of bacilli both on smear and culture, in spite of the possible growth in extended incubation period.
The phenomen of repeated SPCN was found mainly in patients treated with long-term chemotherapy. If colonies grow during the extended incubation in such a case, a risk of deterioration in the future is high and the prognosis is not favourable.
Briefly, it may be concluded that the SPCN cases have no clinical significance, if there is no growth during the extended incubation period.