Identification of a W variant outbreak of Mycobacterium tuberculosis via population-based molecular epidemiology

Context. Typing of Mycobacterium tuberculosis could provide a more sensitive means of identifying outbreaks than use of conventional surveillance techniques alone. Variants of the New York City W strain of M tuberculosis were identified in New Jersey. Objective. To describe the spread of the W family of M tuberculosis strains in New Jersey identified by molecular typing and surveillance data. Design. Population-based cross- sectional study. Setting and Subjects. All incident culture-positive tuberculosis cases reported in New Jersey from January 1996 to September 1998, for which the W family was defined by insertion sequence (IS) IS6110 DNA fingerprinting, polymorphic GC-rich repetitive sequence (PGRS) typing, spacer oligotyping (spoligotyping), and variable number tandem repeat (VNTR) analysis. Main Outcome Measure. Identification and characterization of W family clones supplemented by surveillance data. Results. Isolates from 1207 cases were analyzed, of which 68 isolates (6%) belonged to the W family based on IS6110 and spoligotype hybridization patterns. The IS6110 hybridization patterns or fingerprints revealed that 43 patients (designated group A) shared a unique banding motif not present in other W family isolates. Strains collected from the remaining 25 patients (designated group B), while related to W, displayed a variety of IS6110 patterns and did not share this motif. The PGRS and VNTR typing confirmed the division of the W family into groups A and B and again showed group A strains to be closely related and group B strains to be more diverse. The demographic characteristics of individuals from groups A and B were specific and defined. Group A patients were more likely than group B patients to be US born (91% vs 24%, P<.001), black (76% vs 16%, P<.001), human immunodeficiency virus positive (40% vs 0%, P = .007), and residents of urban northeast New Jersey counties (P<.001). Patients with group B strains were primarily non-US born, of Asian descent, and more dispersed throughout New Jersey. No outbreak had been detected using conventional surveillance alone. Conclusions. The implementation of multiple molecular techniques in conjunction with surveillance data enabled us to identify a previously undetected outbreak in a defined geographical setting. The outbreak isolates comprise members of a distinct branch of the W family phylogenetic lineage. The use of molecular strain typing provides a proactive approach that may be used to initiate, and not just augment, traditional surveillance outbreak investigations.