Phylogenetic associations with drug-resistant Mycobacterium tuberculosis isolates in a paediatric population

SETTING: Department of Microbiology, National Institute of Tuberculosis and Respiratory Diseases, New Delhi, India. OBJECTIVES: As paediatric tuberculosis (TB) is a surrogate marker for actively transmitted disease in a community, we investigated drug resistance patterns of 97 Mycobacterium tuberculosis complex strains isolated from children and explored their phylogenetic associations. DESIGN: A total of 111 paediatric patients who attended the out-patient department during the study period 2009-2011 and whose sputum samples were sent to the Microbiology Department for liquid culture and drug susceptibility testing (DST) were included in this study. DST and spoligotyping were performed on cultures positive for M. tuberculosis complex. RESULTS: DST against four first-line drugs showed that 31 of 97 (32%) strains were pan-susceptible, while 66/97 (68%) were resistant to at least one drug, including 55/97 (56.7%) that were resistant to at least isoniazid and rifampicin (i.e., multidrug-resistant). The majority of the isolates (n = 81/90, 90%) belonged to the principal genetic group 1 strains, the most predominant spoligotyping clusters being spoligotyping international type (SIT) 1/Beijing (n=28), SIT26/CAS1-Delhi (n=27) and SIT53/T1 (n = 6). CONCLUSION: The involvement of Beijing and CAS1-Delhi clades in paediatric TB patients suggests that these two lineages play a major role in ongoing active transmission.