A total of 938 respiratory specimens (633 sputa, 249 bronchial and tracheal aspirates, and 56 bronchoalveolar lavages) from 589 patients were tested for direct detection of Mycobacterium tuberculosis complex by the Gen-Probe amplified Mycobacterium tuberculosis direct test (MTD), and the results were compared with those of the conventional methods of fluorescence microscopy and cultivation (solid and radiometric media). One series of specimens (n = 515) was decontaminated with N-acetyl-L-cysteine (NALC)-NaOH; the other one (n = 423) was decontaminated with sodium dodecyl (lauryl) sulfate (SDS)-NaOH. Of the specimens decontaminated with NALC, 39 were MTD and culture positive, 455 were MTD and culture negative, 18 were MTD positive and culture negative, and 3 were MTD negative and culture positive, indicating a sensitivity of 92.9% and a specificity of 96.2% for the MTD. Of the specimens decontaminated with SDS, 35 were MTD and culture positive, 372 were MTD and culture negative, 15 were MTD positive and culture negative, and 1 was MTD negative and culture positive, indicating a sensitivity of 97.2% and a specificity of 96.1% for the MTD. After resolution of discrepant results by review of the patients' clinical data, the sensitivity of the MTD was 93.9%, the specificity was 97.6%, the positive predictive value was 80.7%, and the negative predictive value was 99.3% for the NALC series; the corresponding values were 97.4, 96.9, 76.0, and 99.7%, respectively, for the SDS series. In conclusion, the MTD is a highly sensitive and specific technique for detecting M. tuberculosis complex within hours in both smear-positive and smear-negative respiratory specimens.

Restriction fragment length polymorphism (RFLP) analysis of Mycobacterium tuberculosis based on the insertion sequence IS6110 has recently been standardized and become an important molecular tool in answering questions such as: 1) transmission of the disease in community [1,2] and international settings [3] as well as via the nosocomial route [4,5]; 2) reactivation versus reinfection of tuberculosis (TB) [6]; and 3) cross contamination of cultures in the laboratory [7].Large population-based studies undertaken in New York [8] and San Francisco [9] utilizing IS6110-based RFLP analyses have revealed clusters, which inferred that recen-tly transmitted TB encompassed 30-40% of TB cases. Even though these large urban areas have a high proportion of patients infected with human immunodeficiency virus (HIV), who are known to be more susceptible to in-fections and at greater risk of latent TB infection rapidly progressing to active disease, these figures greatly exceed general assumptions regarding transmission (~10%; [10]). Both studies concentrating on these big cities are based on the assumptions that deoxyribonucleic acid (DNA) fingerprinting using the IS6110 sequence as a probe provides ac-curate typing of M. tuberculosis isolates and, furthermore, that the identification of cluster strains necessarily implies recent transmission.Most recent concepts of molecular epidemiology utilizing additional genetic markers, such as the polymorphic GC-rich repetitive sequence (PGRS; [11,12]) and/or the 36 base pair (bp) direct repeat (DR; [13,14]) have, however, demonstrated that DNA fingerprinting with the IS-6110 technique was not always sufficient, particularly, in those cases where isolates have fewer than six copies of IS6110 [15][16][17]. Use of supplementary fingerprinting techniques markedly decreased clustering and, thus, put the transmission links suggested by molecular biology more in line with epidemiological data.In the present study RFLP patterns of M. tuberculosis strains isolated from TB patients of the metropolitan area of Zurich (population 1.2 million; area: 1,729 km 2 ) over a period of 3 yrs were analysed to determine the frequency of recent transmission, which eventually reflects the effectiveness of current measures of TB control, i.e., on case finding and management, contact tracing and preventive therapy strategies. Methods Patient populationThe study cohort included 444 patients of the Canton of Zurich, all being treated for TB between 1991 and 1993 (278 males, 166 females; 216 Swiss-born (48.6%), 228 foreign-born (51.4%)). Restriction fragment length polymorphism (RFLP) analysis was performed by using IS6110 and the polymorphic GC-rich sequence (PGRS) as genetic markers. Transmission of tuberculosis in the metropolitan area ofNinety nine isolates shared by 77 patients (21.3%) were associated with 28 IS6110-defined clusters. However, secondary typing of low copy number isolates decreased the number of clusters to 25, encompassing 81 isolates from 63 (17.5%) patients. By deoxyribonucleic acid (DNA) fin...

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