1. Effect of chemotherapy on the appearance of smear-positive and culture-negative acid-fast organisms (SPCN).
The rate of SPCN specimens was higher in hospitalized patients who were receiving antituberculous agents than in newly hospitalized patients before starting chemotherapy (Tablesl-3). The administration of chemotherapy is likely to produce more SPCN specimens, although single administration itself did not influence the rate of SPCN (Table 4).
2. Influence of the medium used for isolating acid-fast organisms.
When compared with the Ogawa egg medium, the use of “Tween egg medium” reduced the rate of SPCN specimens (Tables 2, 5 and 6).
3. Patients excreting SPCN organisms for a long time.
Out of 17 patients who showed 3 times or more the SPCN specimens, 6 were shown to excrete the SPCN organisms frequently and the other 11 showed the SPCN specimens only in the course of ‘complete’ negative conversion (Table 7). The mode of excretion of acid fast organisms in these 6 patients are shown in Table 8, and their background in Table 9. These patients showed positive cultures of
Mycobacterium tuberculosis in the further long-term observation. One example is shown in Table 10.
From the results of the present study, the majority of SPCN organisms are considered as dead bacteria, although a part of them may be alive as seen from the fact that the rate of SPCN specimens has been decreased by an improvement of medium. The SPCN phenomenon appeared usually in the course of negative conversion, but, in a few cases, the phenomenon persisted. These patients showed, when observed for long time, positive cultures of
M. tuberculosis. The continuous excretion of the SPCN specimens is interpreted as excretion of dead bacteria from a lesion where
M. tuberculosis organisms are growing continuously but slowly.
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