Abstract
Based on the results of study on the mode of excretion of ‘atypical’ mycobacteria (mycobacteria other than tubercle bacilli) in patients hospitalized in the National Chubu Hospital for five years (1972 to 1976), criteria of diagnosis for lung disease due to ‘atypical’ mycobacteria have been proposed.
1) The prevalence rate of casual isolates, which were considered to have not caused disease, was estimated in the patients hospitalized for five years. The patients received a total of 36, 243 monthly sputum examinations, and a total of 539 strains of acid-fast organisms other than tubercle bacilli were isolated. Out of these, 235 belonged to casual isolates. The prevalence rate of casual isolates (background-prevalence rate) was estimated at 0.84%, i.e., ca. 1% (Table 1).
2) Rates of isolation of acid-fast organisms other than tubercle bacilli, which are considered to be significantly higher than the background-prevalence rate (0.01), were calculated (Table2). These rates are considered to show an abnormal state of excretion of these organisms. It is suggested that a positive culture of ‘atypical’ mycobacteria at the first examination after hospitalization is an abnormal event, and that two or more positive cultures in 3 to 12 daily or monthly examinations also an abnormal event. The occurrence of these rates may be regarded as an abnormal event irrespectively of the number of colonies on isolation medium. If such abnormal rates are shown in a patient together with an incidence of disease such as appearance of a cavity, fever, cough and sputum, the patient may be regarded to have infection due to the acid-fast organism.
3) Prevalence of the above mentioned unusual rate of isolation does not readily indicate the presence of disease unless demonstrating a co-existing clinical evidence. However, if we can determine an extent of isolations of a pathogenic organism that show certainly the presence of disease, it is possible to make diagnosis based on bacteriological evidence only. In table 3, patients who have excreted three times or more M. avium-intracellulare during a period of a half year are listed. All these patients showed a cavity or a few cavities in accordance with the excretions of the organism and were considered to have disease due to the organism. Thus, the presence of three or more isolations of this organism within six months is considered to show the existence of lung disease due to this organism.
4) In case of non-pathogens, three times or more excretions in a half year or in a year does not show the presence of disease, although the excretions are unusual (Table5). Different organisms may be excreted in the same patients (Table5). The successive excretions of the same organism may be due to a state of parasitism in open-negative cavities or deformed bronchi.
5) Three times excretions of M. avium-intracellulare in the same patients during a period of more than a year are not always signs of disease (Table6). Two or more excretions in 2 to 12 examinations are unusual, but they should not readily be considered to be due to disease (Table7). On the other hand, only a few isolations can serve for diagnosis, if they are unusual and occur concordantly with appearance of clinical signs (Figs.1 and 2).
6) In conclusion, 3 to 10 daily sputum examinations in the first month of hospitalization serve most effectively for diagnosis of disease. Two or more positive cultures of an organism in 3 to 12 examinations may be considered to be unusual, and if they meet with the onset of disease, the presence of disease is probable. In case of M. avium-intracellulare, three or more positive cultures in six monthly examination or in three to six daily examinations show surely the presence of lung disease due to this organism.
