Isolates classified as RDRio or non-RDRio M. tuberculosis by multiplex PCR were further classified as clustered (? isolates) or unique based primarily upon IS6110-RFLP patterns and lineage-specific cluster proportions were calculated. The secondary case rate of RDRio was compared with other prevalent M. tuberculosis lineages. Genotype data were merged with the data from the NYC TB Registry to assess demographic and clinical characteristics.
RDRio strains were found to: (1) be restricted to the Latin American-Mediterranean family, (2) cause approximately 8 % of TB cases in NYC, and (3) be associated with heightened transmission as shown by: (i) a higher cluster proportion compared to other prevalent lineages, (ii) a higher secondary case rate, and (iii) cases in children. Furthermore, RDRio strains were significantly associated with US-born Black or Hispanic race, birth in Latin American and Caribbean countries, and isoniazid resistance.
The RDRio genotype is a single M. tuberculosis strain population that is emerging in NYC. The findings suggest that expanded RDRio case and exposure identification could be of benefit due to its association with heightened transmission.