[Objective] The Committee for Mycobacterial Examinations has programmed and implemented the external quality assessment for Mycobacterium tuberculosis drug susceptibility testing by proficiency testing panel to the commercial laboratories that perform drug susceptibility testing more than 20 cases monthly.
[Method] I t utilized 20 strains, exactly pairs of 10 strains, of Mycobacterium tuberculosis that were evaluated for the resistance pattern in the WHO/IUATLD supra-national laboratory network (SRLN), and the concordant results within SRLN were employed as the gold standard of the test. Each laboratory performedthe drug susceptibility testing with routine method including the preparation of bacterial suspension.
[Results] As a result, the sensitivity for isoniazid (INH) was 95 % on an average, ranging from 29% to 100%. The sp ecificity and efficiency for INH were 100% and 97% (50-100), respectively. Additionally, the reproducibility for INH was 99% (90-100). Similarly, the sensitivity, specificity, effici ency and reproducibility for rifampicin (RFP) were 95% (63?100), 99% (67-100), 97% (70-100) and 98% (90-100), respectively. The sensitivity, specificity, efficiency and reproducibility for streptomycin (SM) were 66% (33-100), 94%(64-100), 86% (65-100) and 96% (80-100), respectively. For EB, the sensitivity, specificity, efficiency and reproducibility were 96% (33-100), 74% (57-86), 81 % (60-90) and 96% (80-100), respectively.
[Discussion] T he required standard for satisfactory results of sensitivity, specificity and reproducibility is 95%, and the results for INH and RFP were excellent on an average. However, several laboratories showed unsatisfactory results, especially in sensitivity. Almost all the discordant results for INH and RFP were false-susceptible comparing to the gold standard. For INH, one pair of tested strain showed discordant results in many evaluated laboratories and seemed to reflect the relatively low concordance even in SRLN. On the other hand, the reason for false-susceptible results for RFP was unclear. Several laboratories showed discordant results in one strain pair so that it might be a technical mistake.
The sensitivity of SM was rema rkably low and it was due to many false-susceptible results, which was twice the number of false-resistance. It was due to the character of tested strain partially considering relatively low concordance in SRLN. However, there was no persuasive explanation for the inconsistency in other strains that showed highly concordant results in SRLN. The difference of critical drug concentration in LOwenstein-Jensen and 1% Ogawa medium might contribut e to the discrepancies.
The specificity of EB was low and it was due to many falseresistant results. About a specific pair of tested strain, almost 100% of laboratories showed concordant false-resista nt results whereas SRLN showed perfectly concordant susceptible result. If this strain was considered as resistant and another strain that showed less than 70% concordance in the tested laboratories was excluded, the sensitivity, specificity and efficiency would improve to 96%, 97% and 97%, respectively.
The proficiency testing is a part of external quality assessment system and requires following corrective actions. A permanent quality improvement and maintenance will be expected through the spiral circulation of quality assurance activities.

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Mycobacterium kansasii infection has been reported to be about 20 percent of non-tuberculous mycobacteriosis, and its disseminated type is uncommon and the prognosis is reported to be generally poor. We experienced one case of disseminated Mycobacterium kansasii infection. A 81 yearold man who had been short-bowel syndrome due to the operation for superior mesenteric artery occlusion since 1998 was admitted on April 24th, 2001 to our hospital because of slowly progressive consciousness disturbance and anorexia. He had shown progressive productive cough and respiratory failure and laboratory findings were C-reactive protein elevation and pancytopenia. Human immunodeficiency virus (HIV) antibody was negative. Chest X-ray and computed tomography showed diffuse miliary nodules and infiltrative shadow. Sputum examination was positive for mycobacteria. The cultured isolate was identified as Mycobacterium kansasii. Bone marrow aspirations revealed inflammatory granuloma with necrosis. He was diagnosed as disseminated Mycobacterium kansasii infection and heart failure, and was treated by anti-tuberculosis drugs and diuretics. Treatment was very effective and Chest X-ray findings and respiratory failure had been completely improved. In this case we speculated that the malnutrition due to short-bowel syndrome could be one of the most suspected reasons of Mycobacterium kansasii dissemination. Disseminated Mycobacterium kansasii infection has been rarely reported comparing with the other mycobacterial infections in Japan. However, due to the increasing numbers of immunocompromised hosts with aging, HIV infection, cancer, and steroid therapy, this type of infection will become more common and its earlier diagnosis and adequate treatment will be important to improve the prognosis.

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To clarify our knowledge about exogenous reinfection of Mycobacterium tuberculosis in HIV-negative persons, we review the literatures on this issue as much as possible, and we deduce the following; 1) Risk of exogenous reinfection may be not rare in itself, but quantifiably determined by host factor, bacilli factor and intensity of exposure.2) Generally, when already-infected persons are exposed to exogenous reinfection Mycobacterium tuberculosis, risk of disease due to the exposure is definitely lower than not-already-infected persons (estimated relative risk: 8.5%). But the protection rate can be similar with that of BCG vaccination under most favorable condition.3) It cannot be concluded definitely that the tuberculosis disease in already-infected persons is almost always due to endogenous reactivation.

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