title: Prevalence of ST26 among untreated smear-positive tuberculosis  patients from Karachi indicating ongoing transmission.
abstract: Tuberculosis (TB) control is a major healthcare priority for Pakistan. We have studied Mycobacterium tuberculosis strains from the sputa of 100 treatment-naïve, smear-positive pulmonary TB cases from Karachi, Pakistan, to identify strains most responsible for active transmission in this population. DNA extracted from M. tuberculosis isolates were subjected to spacer oligotyping (spoligotyping). Sixty-six (66%) clinical isolates were grouped into 9 different clusters. The largest cluster comprised the Central Asian Strain (CAS) 1 or ST26 (n=40). The remaining isolates (34%) had unique spoligotypes. We conclude that ST26 being the most prevalent strain in smear-positive cases contributes greatly towards ongoing transmission in Karachi. Our data further suggest that ST26 may have a selection advantage not afforded by other genotypes. This conclusion is further supported by DESTUS analysis (Detecting Emerging Strains of Tuberculosis Using Spoligotypes) identifying ST26 as the only emerging spoligotype. Reasons for the spread of ST26 require further study.
authors.affiliation: Department of Clinical Microbiology, the Aga Khan University Hospital, Karachi, Pakistan. sadia.shakkoor@aku.edu
authors.forename: Sadia
authors.initials: S
authors.lastname: Shakoor
authors.forename: Mahnaz
authors.initials: M
authors.lastname: Tanveer
authors.forename: Yasraba
authors.initials: Y
authors.lastname: Rafiq
authors.forename: Zahra
authors.initials: Z
authors.lastname: Hasan
authors.forename: Arshad
authors.initials: A
authors.lastname: Javed
authors.forename: Nadeem
authors.initials: N
authors.lastname: Rizvi
authors.forename: Nadeem
authors.initials: N
authors.lastname: Rehman
authors.forename: Rumina
authors.initials: R
authors.lastname: Hasan
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D015373:Bacterial Typing Techniques / Q000379:methods; D016000:Cluster Analysis; D004269:DNA, Bacterial / Q000032:analysis*; D024881:Drug Resistance, Bacterial; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009169:Mycobacterium tuberculosis / Q000145:classification* / Q000235:genetics; D010154:Pakistan / Q000453:epidemiology; D015995:Prevalence; D017422:Sequence Analysis, DNA / Q000379:methods; D014397:Tuberculosis, Pulmonary / Q000453:epidemiology / Q000382:microbiology* / Q000635:transmission
chemical_list: D004269:DNA, Bacterial