Contributory Studies on the Washing Method of Sputum for the Determination of Causative Microbes in the Respiratory Infection

To secure true causatives from the expectorated sputum in respiratory infectious diseases, a washing method of the sputum has been applied in this department of internal medicine. The purpose is to wash out the contaminants.In this paper, the author evaluated this method with basic experiments using 233 and 400 specimens obtained from treated and not yet treated respiratory patients with chemotherapy, respectively.The initial sputum was put in the saline solution in the plate, stirred and broken down into the fine fragments by platinum loop. Several fragments of these were transferred to the next plate and processed as same as above. This procedure was repeated several times. The last fragments were cultured. Nonprocessed sputum was also cultured at the same time in comparison.The results were studied regarding colony-counts, appearance of the sputum, the number of squamous cells, chronological aspects of sputum collecting, reproducibility of the tests. Long term observation was especially done on chronic respiratory patients.The results were summarized as follows:1) Mostly one species, infrequently two species, of “potential pathogens” remained by washing the purulent or mucopurulent sputum. No definite pathogen was obtained from mucous or mucoserous sputum by this method.2) Microscopically, squamous cells in the purulent or mucopurulent sputum were markedly decreased or disappeared by washing, suggesting the elimination of secretion from upper respiratory tract.3) Reproducible results were obtained from purulent and mucopurulent sputum. But this was not the case in mucous and mucoserous sputum.4) It was clear that sputum specimen collected in the morning was preferrable for the etiological test.5) In most cases in which causative pathogen could be estimated sputum was purulent or mucopurulent and squamous cells were markedly decreased by washing.6) Long term observations were done in patients with chronic respiratory infection by repeating this technique (method). It was speculated that in those patients one or two species of “potential pathogens” resided in the upper respiratory tract even during symptom free period and that exacerbation could take place by their invasion down to lower respiratory tract.