Abstract
Tuberculosis (TB) clusters, defined as two or more active TB cases with epidemiological links and the same genotype of Mycobacterium tuberculosis strains, are direct evidence of recent TB transmission. We analyzed TB cases newly diagnosed in 2006–2008, confirmed by the diagnostic laboratory, at a university-affiliated hospital in Taipei metropolitan area where TB is endemic in elderly populations. Numbers of randomly selected non-TB patients (as controls) from each district were proportional to the district population (Pearson's correlation coefficient = 0.8), which supports that patients who visited the hospital represent a spatially independent sample of total population in this area. We used the nearest neighbor hierarchical (NNH) clustering method and the spatial scan statistics to identify spatial TB clusters among 969 cases within the 10-km buffer, adjusting for the elderly population. One cluster with 10 TB cases from different households in geographic proximity to each other was detected by both NNH clustering and spatial scan statistics. Spoligotyping and mycobacterial interspersed repetitive-unit-variable-number tandem-repeat (MIRU-VNTR) genotyping showed that four of the six M. tuberculosis strains from this spatial cluster were identical. Three of those four patients were older than 70 years, but none were nursing home residents. The identical genotypes of M. tuberculosis strains in clustered elderly TB patients living in neighborhoods indicate that recent transmission plays a significant role in TB endemicity among elderly populations in Taiwan.
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