Effectiveness of comprehensive variable number of tandem repeat (VNTR) analysis in areas with a low incidence of tuberculosis]

To ascertain the effectiveness of variable number of tandem repeat (VNTR) analysis in areas with a low incidence of tuberculosis (TB), we examined the combination of comprehensive VNTR analyses and field epidemiological investigation results in Yamagata Prefecture, Japan, where estimated incidence of new TB cases per 100,000 population was 11.3 in 2011.We collected Mycobacterium tuberculosis isolates from 184 (69.2%) of 266 pulmonary TB patients across the whole of Yamagata Prefecture between 2009 and 2011. Next, 24 loci [JATA (12), QUB-11a, ETR A, QUB-18, QUB3232, v3820, v4120, MIRU04, MIRU16, MIRU40, ETR C, Mtub30, Mtub39] in VNTR genotypes were determined. The relationships among TB patients derived from the respective clusters were surveyed using field epidemiological investigation results provided by the Public Health Center.Seventeen clusters were formed by 49 (26.6%) of the 184 isolates. We found 3 hospital infection cases, 3 family infection cases, and 1 nursing home infection case forming 6 clusters. Among these cases, two relationships among patients were revealed after additional epidemiological investigation at the Public Health Center. The VNTR pattern of the largest cluster, which was formed by 12 isolates, was identical with that of an incipient patient of a TB mass infection that occurred in 2007.In areas with a low incidence of TB, a combination of comprehensive VNTR analysis and field epidemiological investigation is useful to find unknown transmission routes, identify for new risk groups, and trace mass infections.