Tuberculosis Genotype Clusters and Transmission in the U.S., 2009-2018

Abstract

Introduction: In the U.S., universal genotyping of culture-confirmed tuberculosis cases facilitates cluster detection. Early recognition of the small clusters more likely to become outbreaks can help prioritize public health resources for immediate interventions.

Methods: This study used national surveillance data reported during 2009-2018 to describe incident clusters (≥3 tuberculosis cases with matching genotypes not previously reported in the same county); data were analyzed during 2020. Cox proportional hazards regression models were used to examine the patient characteristics associated with clusters doubling in size to ≥6 cases.

Results: During 2009-2018, a total of 1,516 incident clusters (comprising 6,577 cases) occurred in 47 U.S. states; 231 clusters had ≥6 cases. Clusters of ≥6 cases disproportionately included patients who used substances, who had recently experienced homelessness, who were incarcerated, who were U.S. born, or who self-identified as being of American Indian or Alaska Native race or of Black race. A median of 54 months elapsed between the first and the third cases in clusters that remained at 3-5 cases compared with a median of 9.5 months in clusters that grew to ≥6 cases. The longer time between the first and third cases and the presence of ≥1 patient aged ≥65 years among the first 3 cases predicted a lower hazard for accumulating ≥6 cases.

Conclusions: Clusters accumulating ≥3 cases within a year should be prioritized for intervention. Effective response strategies should include plans for targeted outreach to U.S.-born individuals, incarcerated people, those experiencing homelessness, people using substances, and individuals self-identifying as being of American Indian or Alaska Native race or of Black race.

Figure 1.

Inclusion and exclusion algorithm for the primary analysis. ^aTB cases for which only one case with that genotype was reported in the same county during 2009–2018. ^bTB clusters were considered pre-existing if there were any cases in the county with matching spoligotype and 24-locus MIRU-VNTR during the 24 months preceding the first case (or matching spoligotype and 12-locus MIRU-VNTR for cases genotyped before 2009). TB, tuberculosis; MIRU-VNTR, mycobacterial interspersed repetitive units variable number of tandem repeats.