A Standardized Approach for Collection of Objective Data to Support Outcome Determination for Late-Phase Tuberculosis Clinical Trials.

Rationale: We developed a standardized method, possible poor treatment response (PPTR), to help ascertain efficacy endpoints in Study S31/A5349 (NCT02410772), an open-label trial comparing two 4-month rifapentine-based regimens with a standard 6-month regimen for the treatment of pulmonary tuberculosis (TB). Objectives: We describe the use of the PPTR process and evaluate whether the goals of minimizing bias in efficacy endpoint assessment and attainment of relevant data to determine outcomes for all participants were achieved. Methods: A PPTR event was defined as the occurrence of one or more prespecified triggers. Each PPTR required initiation of a standardized evaluation process that included obtaining multiple sputum samples for microbiology. Measurements and Main Results: Among 2,343 participants with culture-confirmed drug-susceptible TB, 454 individuals (19.4%) had a total of 534 individual PPTR events, of which 76.6% were microbiological (positive smear or culture at or after 17 wk). At least one PPTR event was experienced by 92.4% (133 of 144) of participants with TB-related unfavorable outcome and between 13.8% and 14.7% of participants with favorable and not-assessable outcomes. A total of 75% of participants with TB-related unfavorable outcomes had microbiological confirmation of failure to achieve a disease-free cure. Conclusions: Standardized methodologies, such as our PPTR approach, could facilitate unbiased efficacy outcome determinations, improve discrimination between outcomes that are related and unrelated to regimen efficacy, and enhance the ability to conduct pooled analyses of contemporary trials.

Four-Month Rifapentine Regimens with or without Moxifloxacin for Tuberculosis.

BACKGROUND: Rifapentine-based regimens have potent antimycobacterial activity that may allow for a shorter course in patients with drug-susceptible pulmonary tuberculosis. METHODS: In an open-label, phase 3, randomized, controlled trial involving persons with newly diagnosed pulmonary tuberculosis from 13 countries, we compared two 4-month rifapentine-based regimens with a standard 6-month regimen consisting of rifampin, isoniazid, pyrazinamide, and ethambutol (control) using a noninferiority margin of 6.6 percentage points. In one 4-month regimen, rifampin was replaced with rifapentine; in the other, rifampin was replaced with rifapentine and ethambutol with moxifloxacin. The primary efficacy outcome was survival free of tuberculosis at 12 months. RESULTS: Among 2516 participants who had undergone randomization, 2343 had a culture positive for Mycobacterium tuberculosis that was not resistant to isoniazid, rifampin, or fluoroquinolones (microbiologically eligible population; 768 in the control group, 791 in the rifapentine-moxifloxacin group, and 784 in the rifapentine group), of whom 194 were coinfected with human immunodeficiency virus and 1703 had cavitation on chest radiography. A total of 2234 participants could be assessed for the primary outcome (assessable population; 726 in the control group, 756 in the rifapentine-moxifloxacin group, and 752 in the rifapentine group). Rifapentine with moxifloxacin was noninferior to the control in the microbiologically eligible population (15.5% vs. 14.6% had an unfavorable outcome; difference, 1.0 percentage point; 95% confidence interval [CI], -2.6 to 4.5) and in the assessable population (11.6% vs. 9.6%; difference, 2.0 percentage points; 95% CI, -1.1 to 5.1). Noninferiority was shown in the secondary and sensitivity analyses. Rifapentine without moxifloxacin was not shown to be noninferior to the control in either population (17.7% vs. 14.6% with an unfavorable outcome in the microbiologically eligible population; difference, 3.0 percentage points [95% CI, -0.6 to 6.6]; and 14.2% vs. 9.6% in the assessable population; difference, 4.4 percentage points [95% CI, 1.2 to 7.7]). Adverse events of grade 3 or higher occurred during the on-treatment period in 19.3% of participants in the control group, 18.8% in the rifapentine-moxifloxacin group, and 14.3% in the rifapentine group. CONCLUSIONS: The efficacy of a 4-month rifapentine-based regimen containing moxifloxacin was noninferior to the standard 6-month regimen in the treatment of tuberculosis. (Funded by the Centers for Disease Control and Prevention and others; Study 31/A5349 ClinicalTrials.gov number, NCT02410772.).

Optimizing drug inventory management with a web-based information system: The TBTC Study 31/ACTG A5349 experience.

INTRODUCTION: Efficient management of study drug inventory shipments is critical to keep research sites enrolling into multisite clinical treatment trials. A standard manual drug-management process used by the Tuberculosis Trials Consortium (TBTC), did not accommodate import permit approval timelines, shipment transit-times and time-zone differences. We compared a new web-based solution with the manual process, during an international 34-site clinical trial conducted by the TBTC and the AIDS Clinical Trials Group (ACTG); TBTC Study 31/ACTG A5349. MATERIAL AND METHODS: We developed and implemented a technological solution by integrating logistical and regulatory requirements for drug importation with statistical simulations that estimated stock-out times in an online Drug Management Module (DMM). We measured the average shipment-related drug stock-outs and time to drug availability, to assess the efficiency of the DMM compared to the manual approach. RESULTS: An Interrupted Time-Series (ITS) analysis showed a 15.4% [p-value = 0.03; 95% C.I. (-28.8%, -2.0%)] reduction in average shipment-related study drug stock-out after DMM implementation. The DMM streamlined the restocking process at study sites, reducing median transit-time for sites associated with a depot by 2 days [95% C.I. (-3.0, -1.0)]. Under the DMM, study drugs were available for treatment assignment on the day received, compared to one day after receipt under the manual process. DISCUSSION: The DMM provided TBTC's Data and Coordinating Center and site staff with more efficient procedures to manage and consistently maintain study drug inventory at enrolling sites. This DMM framework can improve efficiency in future multicenter clinical trials. TRIAL REGISTRATION: This trial was registered with ClinicalTrials.gov (Identifier: NCT02410772) on April 8, 2015.

High-dose rifapentine with or without moxifloxacin for shortening treatment of pulmonary tuberculosis: Study protocol for TBTC study 31/ACTG A5349 phase 3 clinical trial.

INTRODUCTION: Phase 2 clinical trials of tuberculosis treatment have shown that once-daily regimens in which rifampin is replaced by high dose rifapentine have potent antimicrobial activity that may be sufficient to shorten overall treatment duration. Herein we describe the design of an ongoing phase 3 clinical trial testing the hypothesis that once-daily regimens containing high dose rifapentine in combination with other anti-tuberculosis drugs administered for four months can achieve cure rates not worse than the conventional six-month treatment regimen. METHODS/DESIGN: S31/A5349 is a multicenter randomized controlled phase 3 non-inferiority trial that compares two four-month regimens with the standard six-month regimen for treating drug-susceptible pulmonary tuberculosis in HIV-negative and HIV-positive patients. Both of the four-month regimens contain high-dose rifapentine instead of rifampin, with ethambutol replaced by moxifloxacin in one regimen. All drugs are administered seven days per week, and under direct observation at least five days per week. The primary outcome is tuberculosis disease-free survival at twelve months after study treatment assignment. A total of 2500 participants will be randomized; this gives 90% power to show non-inferiority with a 6.6% margin of non-inferiority. DISCUSSION: This phase 3 trial formally tests the hypothesis that augmentation of rifamycin exposures can shorten tuberculosis treatment to four months. Trial design and standardized implementation optimize the likelihood of obtaining valid results. Results of this trial may have important implications for clinical management of tuberculosis at both individual and programmatic levels. TRIAL REGISTRATION: NCT02410772. Registered 8 April 2015,https://www.clinicaltrials.gov/ct2/show/NCT02410772?term=02410772&rank=1.

Nonparticipation reasons in a randomized international trial of a new latent tuberculosis infection regimen.

BACKGROUND/AIMS: Efficient recruitment of eligible participants, optimizing time and sample size, is a crucial component in conducting a successful clinical trial. Inefficient participant recruitment can impede study progress, consume staff time and resources, and limit quality and generalizability or the power to assess outcomes. Recruitment for disease prevention trials poses additional challenges because patients are asymptomatic. We evaluated candidates for a disease prevention trial to determine reasons for nonparticipation and to identify factors that can be addressed to improve recruitment efficiency. METHODS: During 2001-2009, the Tuberculosis Trials Consortium conducted Study 26 (PREVENT TB), a randomized clinical trial at 26 sites in four countries, among persons with latent tuberculosis infection at high risk for tuberculosis disease progression, comparing 3 months of directly observed once-weekly rifapentine plus isoniazid with 9 months of self-administered daily isoniazid. During March 2005-February 2008, non-identifying demographic information, risk factors for experiencing active tuberculosis disease, and reasons for not enrolling were collected from screened patients to facilitate interpretation of trial data, to meet Consolidated Standards of Reporting Trials standards, and to evaluate reasons for nonparticipation. RESULTS: Of the 7452 candidates screened in Brazil, Canada, Spain, and the United States, 3584 (48%) were not enrolled, because of ineligibility (41%), site decision (10%), or patient choice (49%). Among those who did not enroll by own choice, and for whom responses were recorded on whether they would accept treatment outside of the study (n = 1430), 68% reported that they planned to accept non-study latent tuberculosis infection treatment. Among 1305 patients with one or more reported reasons for nonparticipation, study staff recorded a total of 1886 individual reasons (reason count: median = 1/patient; range = 1-9) for why patients chose not to enroll, including grouped concerns about research (24% of 1886), work or school conflicts (20%), medication or health beliefs (16%), latent tuberculosis infection beliefs (11%), and patient lifestyle and family concerns (10%). CONCLUSION: Educational efforts addressing clinical research concerns and beliefs about medication and health, as well as study protocols that accommodate patient-related concerns (e.g. work, school, and lifestyle) might increase willingness to enter clinical trials. Findings from this evaluation can support development of communication and education materials for clinical trial sites at the beginning of a trial to allow study staff to address potential participant concerns during study screening.

Exposure to Latent Tuberculosis Treatment during Pregnancy. The PREVENT TB and the iAdhere Trials.

RATIONALE: Data are limited regarding the safety of 12-dose once-weekly isoniazid (H, 900 mg) plus rifapentine (P, 900 mg) (3HP) for latent infection treatment during pregnancy. OBJECTIVES: To assess safety and pregnancy outcomes among pregnant women who were inadvertently exposed to study medications in two latent tuberculosis infection trials (PREVENT TB or iAdhere) evaluating 3HP and 9 months of daily isoniazid (H, 300 mg) (9H). METHODS: Data from reproductive-age (15-51 yr) women who received one or more study dose of 3HP or 9H in either trial were analyzed. Drug exposure during pregnancy occurred if the estimated date of conception was on or before the last dose date. RESULTS: Of 126 pregnancies (125 participants) that occurred during treatment or follow-up, 87 were exposed to study drugs. Among these, fetal loss was reported for 4/31 (13%) and 8/56 (14%), 3HP and 9H, respectively (difference, 13% - 14% = -1%; 95% confidence interval = -17% to +18%) and congenital anomalies in 0/20 and 2/41 (5%) live births, 3HP and 9H, respectively (difference, 0% - 5% = -5%; 95% confidence interval = -18% to +16%). All fetal losses occurred in pregnancies of less than 20 weeks. Of the total 126 pregnancies, fetal loss was reported in 8/54 (15%) and 9/72 (13%), 3HP and 9H, respectively; and congenital anomalies in 1/37 (3%) and 2/56 (4%) live births, 3HP and 9H, respectively. The overall proportion of fetal loss (17/126 [13%]) and anomalies (3/93 [3%]) were similar to those estimated for the United States, 17% and 3%, respectively. CONCLUSIONS: Among reported pregnancies in these two latent tuberculosis infection trials, there was no unexpected fetal loss or congenital anomalies. These data offer some preliminary reassurance to clinicians and patients in circumstances when these drugs and regimens are the best option in pregnancy or in women of child-bearing potential. This work used the identifying trial registration numbers NCT00023452 and NCT01582711, corresponding to the primary clinical trials PREVENT TB and iAdhere (Tuberculosis Trials Consortium Study 26 and 33).

Factors Associated With Noncompletion of Latent Tuberculosis Infection Treatment: Experience From the PREVENT TB Trial in the United States and Canada.

BACKGROUND: Overall rates of noncompletion of treatment (NCT) for latent tuberculosis infection (LTBI) in the PREVENT TB trial were 18% for 3 months of directly observed once-weekly rifapentine (maximum dose, 900 mg) plus isoniazid (maximum dose, 900 mg) (3HP-DOT) and 31% for 9 months of daily self-administered isoniazid (maximum dose, 300 mg; 9H-SAT). NCT for LTBI reduces its effectiveness. The study objective was to assess factors associated with NCT for LTBI among adult participants enrolled at US and Canadian sites of the PREVENT TB trial. METHODS: This was a post hoc exploratory analysis of the randomized, open-label PREVENT TB trial. Factors were analyzed by univariate and multivariate logistic regression (with enrollment site as a random effect). RESULTS: From 6232 participants analyzed, 1406 (22.6%) did not complete LTBI treatment (317 NCT attributed to an adverse event [NCT-AE] and 1089 NCT attributed to reasons other than an adverse event [NCT-O]). The proportion of NCT-AE was similar with both regimens (3HP-DOT = 6.4% vs 9H-SAT = 5.9%; P = .23); NCT-O was higher among participants enrolled in 9H-SAT (9H-SAT = 24.5% vs 3HP-DOT = 12.7%; P = .02). Among those in the NCT-AE group, being non-Hispanic and receiving 3HP-DOT, having cirrhosis and receiving 9H-SAT, alcohol consumption among men, and use of concomitant medication were associated with NCT-AE. Among those in the NCT-O group, receiving 9H-SAT, missing ≥1 early visit, men receiving 9H-SAT, men with a history of incarceration, alcohol abuse, use ever of intravenous drugs, younger age receiving 9H-SAT, and smoking were associated with NCT-O. CONCLUSIONS: Factors associated with NCT, such as missing a clinic visit early during treatment, might help identify persons for whom tailored interventions could improve completion of LTBI treatment. CLINICAL TRIALS REGISTRATION: NCT00023452.

Treatment for preventing tuberculosis in children and adolescents: a randomized clinical trial of a 3-month, 12-dose regimen of a combination of rifapentine and isoniazid.

IMPORTANCE: Three months of a once-weekly combination of rifapentine and isoniazid for treatment of latent tuberculosis infection is safe and effective for persons 12 years or older. Published data for children are limited. OBJECTIVES: To compare treatment safety and assess noninferiority treatment effectiveness of combination therapy with rifapentine and isoniazid vs 9 months of isoniazid treatment for latent tuberculosis infection in children. DESIGN, SETTING, AND PARTICIPANTS: A pediatric cohort nested within a randomized, open-label clinical trial conducted from June 11, 2001, through December 17, 2010, with follow-up through September 5, 2013, in 29 study sites in the United States, Canada, Brazil, Hong Kong (China), and Spain. Participants were children (aged 2-17 years) who were eligible for treatment of latent tuberculosis infection. INTERVENTIONS: Twelve once-weekly doses of the combination drugs, given with supervision by a health care professional, for 3 months vs 270 daily doses of isoniazid, without supervision by a health care professional, for 9 months. MAIN OUTCOMES AND MEASURES: We compared rates of treatment discontinuation because of adverse events (AEs), toxicity grades 1 to 4, and deaths from any cause. The equivalence margin for the comparison of AE-related discontinuation rates was 5%. Tuberculosis disease diagnosed within 33 months of enrollment was the main end point for testing effectiveness. The noninferiority margin was 0.75%. RESULTS: Of 1058 children enrolled, 905 were eligible for evaluation of effectiveness. Of 471 in the combination-therapy group, 415 (88.1%) completed treatment vs 351 of 434 (80.9%) in the isoniazid-only group (P = .003). The 95% CI for the difference in rates of discontinuation attributed to an AE was -2.6 to 0.1, which was within the equivalence range. In the safety population, 3 of 539 participants (0.6%) who took the combination drugs had a grade 3 AE vs 1 of 493 (0.2%) who received isoniazid only. Neither arm had any hepatotoxicity, grade 4 AEs, or treatment-attributed death. None of the 471 in the combination-therapy group developed tuberculosis vs 3 of 434 (cumulative rate, 0.74%) in the isoniazid-only group, for a difference of -0.74% and an upper bound of the 95% CI of the difference of +0.32%, which met the noninferiority criterion. CONCLUSIONS AND RELEVANCE: Treatment with the combination of rifapentine and isoniazid was as effective as isoniazid-only treatment for the prevention of tuberculosis in children aged 2 to 17 years. The combination-therapy group had a higher treatment completion rate than did the isoniazid-only group and was safe. TRIAL REGISTRATION: clinicaltrials.gov Identifier: NCT00023452.

Evaluation of the Informed Consent Process of a Multicenter Tuberculosis Treatment Trial.

BACKGROUND: Ethical principles obligate researchers to maximize study participants' comprehension during the informed consent process for clinical trials. A pilot evaluation of the consent process was conducted during an international clinical trial of treatment for pulmonary tuberculosis to assess the feasibility of conducting an evaluation in a larger population and to guide these future efforts. METHODS: Study staff administered an informed consent assessment tool (ICAT) to a convenience sample of trial participants, measuring comprehension of consent components as derived from the Common Rule and FDA Title 21 Part 50, and satisfaction with the process. Participating site staff completed a consent process questionnaire about consent practices at their respective sites and provided improvement recommendations. ICAT scores and corresponding practices were compared where both were completed. RESULTS: ICATs (n = 54) were submitted from one site in Spain (n = 10), one in Uganda (n = 30), and five in the United States (n = 14). Participants were primarily male (76%), born in Africa (n = 31, 57%), and had a median age of 27 years (interquartile range [IQR]: 24-42). Median ICAT scores were 80% (IQR: 67-93) for comprehension and 89% (IQR: 78-100) for satisfaction. Ugandan participants scored higher than participants from other sites on comprehension (87% vs. 64%) and satisfaction (100% vs. 78%). Staff from 14 sites completed consent process questionnaires. Median ICAT scores for comprehension and satisfaction were higher at sites that utilized visual aids. Practice recommendations included shorter forms, simpler documents, and supplementary materials. CONCLUSIONS: Participants achieved high levels (≥80%) of comprehension and satisfaction with their current consent processes. Higher ICAT scores at one site suggest an additional evaluation may identify approaches to improve comprehension and satisfaction in future trials. Through this pilot evaluation, complexities and challenges were identified in obtaining consent in a large, international multicenter trial and provided insights for a more robust assessment of the consent process in future trials.

What is the most reliable solid culture medium for tuberculosis treatment trials?

We conducted a prospective study to determine which solid medium is the most reliable overall and after two months of therapy to detect Mycobacterium tuberculosis complex (MTB). MTB isolation and contamination rates on LJ and Middlebrook 7H10 and 7H11 agar with and without selective antibiotics were examined in a single laboratory and compared against a constructed reference standard and MGIT 960 results. Of 50 smear positive adults with pulmonary TB enrolled, 45 successfully completed standard treatment. Two spot sputum specimens were collected before treatment and at week 8 and one spot specimen each at weeks 2, 4, 6, and 12. The MTB recovery rate among all solid media for pre-treatment specimens was similar. After 8 weeks, selective (S) 7H11 had the highest positivity rate. Latent class analysis was used to construct the primary reference standard. The 98.7% sensitivity of 7H11S (95% Wilson confidence interval 96.4%-99.6%) was highest among the 5 solid media (P = 0.003 by bootstrap); the 82.6% specificity of 7H10S (95% CI 75.7%-87.8%) was highest (P = 0.098). Our results support 7H11S as the medium of choice. Further studies in different areas where recovery and contamination are likely to vary, are recommended.

How we determined the most reliable solid medium for studying treatment of tuberculosis.

Phase 2 clinical trials for tuberculosis (TB) treatment require reliable culture methods to determine presence or absence of Mycobacterium tuberculosis (Mtb) over the course of therapy, as these trials are based primarily on bacteriological endpoints. We evaluate which of 5 solid media is most reliable: Lowenstein-Jensen (LJ) egg-base medium and 4 Middlebrook agar media (nonselective 7H10 and 7H11 and selective 7H10 and 7H11). We analyze 393 specimens from 50 HIV-negative Ugandan adults with newly-diagnosed, pulmonary TB and high acid-fast bacillus smear grade. Specimens were collected every 2-4 weeks during the first 12 weeks of therapy. We compare the results for each culture to 2 composite reference standards--one that was deemed positive if any solid culture was positive for Mtb and another based on latent-class analysis. Both reference standards established that the 2 selective Middlebrook media most reliably determine the presence or absence of Mtb (P < 0.003), largely because of their lower contamination rates. We also showed that results on Middlebrook media were similar to each other, while LJ was most frequently discordant. Contaminated results appeared more likely to be truly negative than to harbor undetected Mtb.

The association between symptoms and microbiologically defined response to tuberculosis treatment.

RATIONALE: The lack of consistent associations between clinical outcomes and microbiological responses to therapy for some infectious diseases has raised questions about the adequacy of microbiological endpoints for tuberculosis treatment trials. OBJECTIVES: To evaluate the association between symptoms and microbiological response to tuberculosis treatment. METHODS: We performed a retrospective analysis of four clinical trials in which participants had culture-positive tuberculosis, standardized symptom assessment, and follow-up mycobacterial cultures. Two trials (studies 22 and 23) followed participants to identify recurrent tuberculosis; participants in studies 27 and 28 were only followed to treatment completion. MEASUREMENTS AND MAIN RESULTS: This analysis included 1,978 participants; 39 (2.0%) had culture-confirmed treatment failure, and 75 (3.9%) had culture-confirmed recurrence. Productive cough was associated with indices of increased mycobacterial burden at diagnosis (acid-fast smear grade, severity of radiographic abnormalities). Fever and sweats improved rapidly with treatment, whereas productive cough decreased more slowly and was present in 20% of visits after treatment completion. During treatment, study participants with productive cough more often had concurrent culture positivity compared with those without productive cough (studies 22 and 23: adjusted odds ratio, 1.80; 95% confidence interval [CI], 1.33-2.44). Finally, symptoms during the latter part of treatment and follow-up were associated with culture-confirmed treatment failure and recurrence in studies 22 and 23 (for cough: adjusted hazard ratio, 2.07; 95% CI, 1.23-3.49; for fever: adjusted hazard ratio, 5.05; 95% CI, 2.76-9.19). CONCLUSIONS: There are consistent relationships between symptoms and microbiological indices of tuberculosis, including measures of mycobacterial burden at baseline, culture positivity during treatment, and time to culture-confirmed treatment failure and recurrence.

Evaluation of a high-throughput repetitive-sequence-based PCR system for DNA fingerprinting of Mycobacterium tuberculosis and Mycobacterium avium complex strains.

Repetitive-sequence-based PCR (rep-PCR) is useful for generating DNA fingerprints of diverse bacterial and fungal species. Rep-PCR amplicon fingerprints represent genomic segments lying between repetitive sequences. A commercial system that electrophoretically separates rep-PCR amplicons on microfluidic chips, and provides computer-generated readouts of results has been adapted for use with Mycobacterium species. The ability of this system to type M. tuberculosis and M. avium complex (MAC) isolates was evaluated. M. tuberculosis strains (n = 56) were typed by spoligotyping with rep-PCR as a high-resolution adjunct. Results were compared with those generated by a standard approach of spoligotyping with IS6110-targeted restriction fragment length polymorphism (IS6110-RFLP) as the high-resolution adjunct. The sample included 11 epidemiologically and genotypically linked outbreak isolates and a population-based sample of 45 isolates from recent immigrants to Seattle, Wash., from the African Horn countries of Somalia, Eritrea, and Ethiopia. Twenty isolates exhibited unique spoligotypes and were not analyzed further. Of the 36 outbreak and African Horn isolates with nonunique spoligotypes, 23 fell into four clusters identified by IS6110-RFLP and rep-PCR, with 97% concordance observed between the two methods. Both approaches revealed extensive strain heterogeneity within the African Horn sample, consistent with a predominant pattern of reactivation of latent infections in this immigrant population. Rep-PCR exhibited 89% concordance with IS1245-RFLP typing of 28 M. avium subspecies avium strains. For M. tuberculosis as well as M. avium subspecies avium, the discriminative power of rep-PCR equaled or exceeded that of RFLP. Rep-PCR also generated DNA fingerprints from M. intracellulare (n = 8) and MAC(x) (n = 2) strains. It shows promise as a fast, unified method for high-throughput genotypic fingerprinting of multiple Mycobacterium species.

Expanded geographical distribution of the N family of Mycobacterium tuberculosis strains within the United States.

The N and W-Beijing families of Mycobacterium tuberculosis are phylogenetically closely related. The ability of the W-Beijing family to rapidly cause widespread disease is well described; however, few outbreaks involving the N family have been reported outside the New York City, N.Y., area. During 2002 to 2003, Seattle, Wash., experienced a rapidly expanding tuberculosis outbreak involving 38 persons in a 23-month period. The outbreak strain, SBRI9, exhibited the genotypic properties of the N family. Its IS6110 restriction fragment length polymorphism pattern was identical or nearly identical to those of two N family strains that were responsible for clusters of tuberculosis cases, including a large nosocomial outbreak, in New York City and New Jersey from 1989 to 1990. It was also identical to strains involved in late 1990s tuberculosis cases in Michigan, Maryland, and Arkansas. Further monitoring of the N family may show that it shares with the W-Beijing family the propensity to spread rapidly, suggesting that this characteristic evolved prior to the divergence of the two genetic lineages.