Molecular epidemiology of Mycobacterium tuberculosis in East Lancashire 2001-2009.

BACKGROUND: East Lancashire has had high rates of tuberculosis for 40 years. The ethnically diverse population is predominantly of South Asian and white origin. Drug resistance data from 1960 to 1999 indirectly suggest that no significant inter-ethnic transmission has occurred. This study used mycobacterial interspersed repetitive unit variable number tandem repeat (MIRU-VNTR) fingerprinting to assess clustering within and between ethnic groups. METHODS: All isolates of Mycobacterium tuberculosis from January 2001 to July 2009 from East Lancashire postcode areas were MIRU-VNTR fingerprinted. Clusters of strains with indistinguishable profiles were also assessed epidemiologically, and their MIRU-VNTR profiles compared with the UK M tuberculosis Strain Typing Database. RESULTS: 332 strains were typed (63 white patients, and 269 non-white patients). 198 MIRU-VNTR profiles were identified, with 144 profiles occurring only once. The typing clustered 187 strains into 53 clusters indistinguishable at all 12 loci and these were further characterised using the exact tandem repeat loci A, B, and C. The 15 loci clustered 32/63 (50.8%) of white and 110/269 (40.9%) of non-white cases and all but nine clusters were of the same ethnicity. The nine inter-racial clusters were further assessed from an epidemiological and clinical perspective and fingerprinting using nine additional loci. Isolates within two of the clusters were further discriminated using the additional nine loci. However, the additional loci did not further discriminate the isolates in the other seven inter-racial clusters. CONCLUSIONS: MIRU-VNTR fingerprinting indicates that although there is evidence of a high rate of transmission within the South Asian sub-population, the data suggest that there is little inter-ethnic transmission.

Improved differentiation of Mycobacterium tuberculosis isolates in the north of England using additional variable number tandem repeat loci.

Mycobacterial interspersed repetitive unit-variable number tandem repeat (MIRU-VNTR) genotyping of over 3300 Mycobacterium tuberculosis isolates from the north of England has identified large clusters of strains which share common profiles. However, many apparent clusters identified when typed using the existing 15 loci lack clear epidemiological links. This study seeks to discover whether or not six additional VNTR loci can increasethe discriminatory power of the existing MIRU-VNTR 15-loci technique. Two hundred and six M. tuberculosis isolates were genotyped, including 57 isolates from 20 epidemiologically linked clusters and 149 from unlinked patients belonging to six large MIRU-VNTR-defined clusters. The discriminatory power of the six additional loci was high (Hunter Gaston Discriminatory Index [HGDI]: 0.952). Five of the six loci were highly discriminative (h > 0.6); however, locus 2401 was less discriminative (h = 0.5). The additional VNTR loci were able to subtype all six unlinked common MIRU-VNTR clusters into 56 subclusters, significantly differentiating unrelated strains in a set previously incorrectly clustered using 15 MIRU-VNTR loci. The largest cluster size was 14 (9.3%) when typed using the six additional VNTR loci, compared to 30 (20%) when typed using the original 15 MIRU-VNTR loci. The same loci were also found to be stable as a result of their inability to subdivide any of the epidemiologically linked clusters. This study has demonstrated that expanding the MIRU-VNTR panel beyond the 15 previously used loci significantly increases the discriminatory power of the technique and thus provides a valuable tool in the epidemiological monitoring of this disease.