Identifying areas and risk groups with localised Mycobacterium tuberculosis transmission in northern England from 2010 to 2012: spatiotemporal analysis incorporating highly discriminatory genotyping data.

Background: Information on geographical variation in localised transmission of TB can inform targeting of disease control activities. The aim of this study was to estimate the proportion of TB attributable to localised transmission for the period 2010-2012 in northern England and to identify case characteristics associated with spatiotemporal-genotypical clusters.
Methods: We combined genotyping data with spatiotemporal scan statistics to define an indicator of localised TB transmission and identified factors associated with localised TB transmission thus defined in a multivariable logistics regression model.
Results: The estimated proportion of TB cases in northern England attributable to localised transmission was 10% (95% CI 9% to 12%). Clustered cases (cases which were spatiotemporally clustered with others of identical genotype) were on average younger than non-clustered cases (mean age 34 years vs 43 years; p value <0.05). Being UK born (adjusted OR (aOR) 3.6, 95% CI 2.9 to 6.0), presenting with pulmonary disease (aOR 2.2, 95% CI 1.3 to 3.6) and history of homelessness (aOR 2.8, 95% CI 1.2 to 6.8) or incarceration (aOR 2.6, 95% CI 1.2 to 5.9) were independently associated with being part of a spatiotemporal-genotypical cluster in a multivariable model. Belonging to an ethnic group other than white or mixed/other was also significantly associated with localised transmission. We identified localised transmission in 103/1958 middle super output areas mostly in urban areas.
Conclusions: Incorporating highly discriminatory genotyping data into spatiotemporal analysis of TB incidence is feasible as part of routine surveillance and can provide valuable information on groups at greater risk and areas with localised transmission of TB, which could be used to inform control measures, such as intensified contact tracing.
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