Genotyping indicates marked heterogeneity of tuberculosis transmission in the United States, 2009-2018

Heterogeneity in the number of secondary tuberculosis (TB) cases per source case, the effective reproductive number, R, is important in modelling prevention strategies' impact on incidence. We estimated mean R (R-m) and calculate the dispersion parameter of this distribution, k, using surveillance and genotyping data for U.S. cases during 2009-2018. We modelled transmission assuming cases in a cluster have matching genotypes and share characteristics related to geography, temporal proximity (i.e. serial interval) and time since U.S. arrival among non-U.S.-born persons. Complete data were available for 55 330/85 958 cases. Varying the serial interval and geographic proximity used to derive clusters, we consistently estimated R(m)k < 0.08; the low value of k indicates a small number of source cases produce a disproportionate number of secondary cases. U.S. TB reproductive number has a highly skewed distribution, indicating a minority of source cases disproportionately contribute to transmission.