Abstract
BackgroundMolecular epidemiology of Mycobacterium tuberculosis, its transmission dynamics and population structure have become important determinants of targeted tuberculosis control programs. Here we describe recent changes in the distribution of M. tuberculosis genotypes in New South Wales (NSW), Australia and compared strain types with drug resistance, site of disease and demographic data.MethodsWe evaluated all culture-confirmed newly identified tuberculosis cases in NSW, Australia, from 2010-2012. M. tuberculosis population structure and clustering rates were assessed using 24-loci Mycobacterial interspersed repetitive unit (MIRU) analysis and compared to MIRU data from 2006-2008.ResultsOf 1177 tuberculosis cases, 1128 (95.8%) were successfully typed. Beijing and East African Indian (EAI) lineage strains were most common (27.6% and 28.5%, respectively) with EAI strains increasing in relative abundance from 11.8% in 2006-2008 to 28.5% in 2010-2012. Few cases of multi-drug resistant tuberculosis were identified (18; 1.7%). Compared to 12-loci, 24-loci MIRU provided improved cluster resolution with 695 (61.6%) and 227 (20.1%) clustered cases identified, respectively. Detailed analysis of the largest cluster identified (an 11 member Beijing cluster) revealed wide geographic diversity in the absence of documented social contact.ConclusionsEAI strains of M. tuberculosis recently overtook Beijing family as a prevalent cause of tuberculosis in NSW, Australia. This lineage appeared to be less commonly related to multi-drug resistant tuberculosis as compared to Beijing strain lineage. The resolution provided by 24-loci MIRU typing was insufficient for reliable assessment of transmissions, especially of Beijing family strains.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2334-14-455) contains supplementary material, which is available to authorized users.
Highlights
Molecular epidemiology of Mycobacterium tuberculosis, its transmission dynamics and population structure have become important determinants of targeted tuberculosis control programs
Study setting and design We report data from ongoing prospective surveillance conducted by the New South Wales (NSW) Mycobacterial Reference Laboratory (MRL) at the Institute of Clinical Pathology and Medical Research (ICPMR) in Sydney, Australia
A total of 1192 patients were identified with cultureconfirmed M. tuberculosis complex between January 2010 and December 2012; 1177 with M. tuberculosis, 1 with M. bovis and 14 with M. bovis BCG. (Figure 1) Of those with M. tuberculosis, 1128 (95.8%) were successfully strain typed and included in population structure comparisons and cluster analysis
Summary
Molecular epidemiology of Mycobacterium tuberculosis, its transmission dynamics and population structure have become important determinants of targeted tuberculosis control programs. We describe recent changes in the distribution of M. tuberculosis genotypes in New South Wales (NSW), Australia and compared strain types with drug resistance, site of disease and demographic data. The global tuberculosis incidence rate has been declining at ~2% per year since 2002, the impact of control efforts remains limited in areas affected by poverty, human immunodeficiency virus infection or drug resistance in Mycobacterium tuberculosis [1,2]. The state of New South Wales (NSW) report the highest absolute number of tuberculosis cases within Australia, but disease rates are highly variable [4]. Tuberculosis incidence rates in excess of 60/100,000 in parts of metropolitan Sydney represent concentrated pockets of imported disease, which may support local transmission [6] .The NSW Mycobacterial Reference Laboratory (MRL) provides ongoing laboratory surveillance to help identify local tuberculosis outbreaks and guide public health responses. Its discriminatory power varies depending on the M. tuberculosis population structure and the number of loci used, for example 24-loci MIRU is more discriminatory than 12 and 15-loci MIRU [8,9]
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