title: Reduced transmissibility of East African Indian strains of Mycobacterium tuberculosis.
abstract: BACKGROUND
  Mycobacterium tuberculosis (MTB) has been classified into 4 main lineages. Some reports have associated certain lineages with particular clinical phenotypes, but there is still insufficient information regarding the clinical and epidemiologic implications of MTB lineage variation.
  
  
  METHODS
  Using large sequence polymorphisms we classified MTB isolates from a population-based study in Montreal, Canada into the 4 major lineages, and identified the associated clinical and epidemiologic features. In addition, IS6110-RFLP and spoligotyping were used as indicators of recent TB transmission. The study population was divided into a derivation cohort, diagnosed between 2001 and 2007, and a separate validation cohort, diagnosed between 1996 and 2000.
  
  
  RESULTS
  In the derivation cohort, when compared to the other MTB lineages, the East African-Indian (EAI) lineage was associated with lower rates of TB transmission, as measured by: positive TST among close contacts of pulmonary TB cases (adjusted odds ratio 0.6: [95% confidence interval 0.4-0.9]), and clustered TB cases (0.3: [<0.001-0.6]). Severe forms of TB were also less likely among the EAI group (0.4: [<0.001-0.8]). There were no significant differences when comparing patients with the other MTB lineages. In the validation cohort, the EAI lineage was associated with lower rates of positive TST among contacts (0.5: [0.3-0.9]) and a trend towards less clustered TB cases (0.5: [0.1-1.8]) when compared to the other lineages. Disease severity among the different groups was not significantly different in the validation cohort.
  
  
  CONCLUSIONS
  We conclude that in Montreal, EAI strains were associated with reduced transmission compared to other MTB lineages.
authors.affiliation: Respiratory Epidemiology and Clinical Research Unit, Montreal Chest Institute, McGill University, Montreal, Quebec, Canada.
authors.forename: Amr S
authors.initials: AS
authors.lastname: Albanna
authors.forename: Michael B
authors.initials: MB
authors.lastname: Reed
authors.forename: Kimberley V
authors.initials: KV
authors.lastname: Kotar
authors.forename: Ashley
authors.initials: A
authors.lastname: Fallow
authors.forename: Fiona A
authors.initials: FA
authors.lastname: McIntosh
authors.forename: Marcel A
authors.initials: MA
authors.lastname: Behr
authors.forename: Dick
authors.initials: D
authors.lastname: Menzies
mesh_terms: D000328:Adult; D015373:Bacterial Typing Techniques; D002170:Canada / Q000453:epidemiology; D016172:DNA Fingerprinting; D004269:DNA, Bacterial / Q000235:genetics; D024881:Drug Resistance, Bacterial; D005260:Female; D005838:Genotype; D006801:Humans; D008297:Male; D008875:Middle Aged; D017720:Molecular Epidemiology / Q000639:trends*; D009169:Mycobacterium tuberculosis / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification; D012150:Polymorphism, Restriction Fragment Length; D012720:Severity of Illness Index; D014376:Tuberculosis / Q000453:epidemiology* / Q000382:microbiology* / Q000635:transmission; D054928:Validation Studies as Topic; D055815:Young Adult
chemical_list: D004269:DNA, Bacterial