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The World Wide Web has become a source of information for clinicians and researchers about virtually every aspect of tuberculosis (TB). We provide information about TB-related Internet portal sites. We classify selected TB-related Web pages according to user needs. The questions that we address are as follows: (1) Where can I find scientific information about TB? (2) Where can I find epidemiologic data? (3) Where can I find literature for laypeople? (4) Where can I find recommendations, guidelines, and clinical decision-making algorithms for management of TB? (5) Where can I find research databases? (6) Where can I find research groups? (7) Where can I find resources for research, teaching, and training? (8) Where can I find information about regulatory action? The total number of TB-related Web pages is immense, their scope is vast, and their content is perpetually changing. Nonetheless, the sites identified here provide the reader with a manageable number of entry points to this increasingly important resource.

Molecular epidemiologic studies of infectious pathogens 1) generate genetic patterns from a collection of microorganisms, 2) compare the degree of similarity among these patterns, and 3) infer from these similarities infectious disease transmission patterns. The authors propose a quantitative approach using genetic distances to study the degree of similarity between patterns. Benefits of such genetic distance calculations are illustrated by an analysis of standard DNA fingerprints of Mycobacterium tuberculosis in San Francisco collected during the period 1991-1997. Graphical representation of genetic distances can assist in determining if the disappearance of a specific pattern in a community is due to interruption of transmission or ongoing evolution of the microorganism's fingerprint. Genetic distances can also compensate for varying information content derived by DNA fingerprints of contrasting pattern complexity. To study demographic and clinical correlates of transmission, the authors calculated the smallest genetic distance from each patient sample to all other samples. With correlation of genetic distances and nearest genetic distances with previously understood notions of the epidemiology of M. tuberculosis in San Francisco, factors influencing transmission are investigated.

Background: Tuberculosis (TB) rates remain high in regions of Southern Mexico despite the existence of a National Tuberculosis Program. Understanding TB epidemiology in such settings would assist in the design of improved TB control and highlight the challenges confronting TB control in developing countries., Methods: We conducted a retrospective review of treatment control cards from 1991 to 1994 in five municipalities in a semiurban region of Southern Mexico., Results: The relatively high rate of TB observed, 42.6 per 100,000 inhabitants, did not change significantly during the study period. Cure rates among new cases were 79% and significantly lower among retreatment cases (62%). Directly observed therapy (DOT) was administered to 84% of patients. Approximately one-half of the retreatment cases who were not cured were compliant with therapy, suggesting that drug resistance contributed to these poor results. Of particular concern was a core group of 16 patients who had received at least three treatments., Conclusions: This region of Mexico has persistently high TB rates despite a DOT-based TB control programme which achieves an overall cure rate of 77%. There exist many retreatment cases for whom cure rates are significantly lower. These cases may serve as a core group for the dissemination of drug resistant TB. The control programme is being reinforced by a nominal register of patients, decreasing administrative barriers for drug supply to individual patients and the availability of mycobacteria cultures. In addition to these measures, in regions which are approaching the levels of efficacy recommended by the WHO it may be appropriate to consider focusing efforts on the identification and treatment of chronic cases.

To assess genotype stability in Mycobacterium tuberculosis, DNA genotypes were compared in sequential isolates from 49 patients who had sputum cultures separated by at least 90 days that grew M. tuberculosis. By use of IS6110 and the polymorphic GC-rich sequence (PGRS) as markers, it was found that paired isolates from 14 (29%) of 49 patients showed changes in their DNA genotypes between isolates (12 in IS6110 genotypes and 2 in PGRS genotypes). Changed IS6110 genotypes were confined to strains with 8-14 bands and were not related to the bacterial drug susceptibility, the patients' human immunodeficiency virus serostatus, or adherence to therapy. Although this rate of change complicates the interpretation of molecular epidemiologic studies, it can be exploited to gain additional insight into disease transmission. Furthermore, IS6110-related mutations may be a major source of genetic plasticity in M. tuberculosis and provide insights into the organism's evolution and virulence.

The propensity of Mycobacterium tuberculosis genotypes to spread across geographic boundaries was investigated by comparing the IS6110 and polymorphic GC-rich sequence patterns of M. tuberculosis isolates from San Francisco and the East Bay, two distinct regions separated by San Francisco Bay. Of 724 isolates from incident tuberculosis patients during 1992 and 1993, only 53 (7.3%) had patterns matching > or = 1 isolates from the other region. In the multivariable analysis of patient risk factors, an AIDS diagnosis (odds ratio [OR], 1.89; 95% confidence interval [CI], 1.00-3.57) and non-Asian race (OR, 3.43; 95% CI, 1.59-7.42) were associated with having an isolate with a matching pattern. Of 375 unique IS6110 patterns among San Francisco isolates, only 9 (2.4%) matched patterns of East Bay isolates. These population-based data suggest that in the San Francisco Bay Area, M. tuberculosis does not rapidly spread across geographic boundaries, and tuberculosis control efforts should focus on transmission within defined areas.

In just a few years, molecular fingerprinting of Mycobacterium tuberculosis has provided clinicians with significant insight into the epidemiology of tuberculosis. This methodology has allowed for a new understanding of the extent of new transmission of tuberculosis among residents of various communities and within institutions. It has also allowed for differentiation between episodes of reinfection and relapse, a task hitherto almost impossible to accomplish. In addition, molecular fingerprinting has allowed assessment of situations where laboratory cross-contamination is suspected. Thus, this technology has in many ways made clinicians reexamine many of their long-held beliefs regarding tuberculosis. In this report, Drs. Behr and Small provide a lucid description of molecular fingerprinting of M. tuberculosis, its current uses, and its future potential value.

To ascertain the role of human immunodeficiency virus (HIV) and Mycobacterium tuberculosis transmission on multidrug-resistant (MDR) tuberculosis (TB) emergence in New York City, medical records, drug susceptibilities, and restriction fragment length polymorphisms (RFLPs) of TB cases at a city hospital between two 9-month periods (1987-1988 and 1990-1991) were reviewed. The proportion of TB patients with MDRTB increased from 10% (27/267) to 17% (38/222; P = .03). Among MDRTB patients of known HIV status, the proportion with HIV increased from 16% (3/19) to 58% (22/38; P = .006). HIV-infected MDRTB patients were more likely than the seronegative ones to have initial MDRTB (88% vs. 56%; P = .03). Among 56 MDR cases with RFLP results, 12 had unique patterns; 44 belonged to one of six clusters. During 1990-1991, 27 (75%) of 36 MDRTB patients were infected with strains isolated from HIV-seronegative patients during 1987-1988. The increase in MDRTB caused by transmission from immunocompetent to immunocompromised persons underscores the urgency of TB control in populations with increasing HIV prevalence.