Reported Tuberculosis in the United States, 2020

Return to Main Menu

Genotype Clusters


Clusters of TB cases with matching genotypes are an indication of possible recent TB transmission.

  • In this report, a TB case is clustered if it had a matching genotype with one or more other cases in the same county or county-equivalent area during the 3-year period of 2018–2020.

The number of reported TB cases that were genotyped declined from 6,966 in 2019 to 5,551 in 2020, a 20.3% reduction mirroring overall case count declines. However, similar to previous years, 97.5% of culture positive cases were associated with a genotype in 2020 (TB Genotyping Surveillance Coverage: United States 2004–2020).

During 2018–2020, 19.0% of TB cases were clustered.

  • The highest percentages of genotype-clustered cases continue to be observed among American Indian or Alaska Native persons (53.4%) and Native Hawaiian or Other Pacific Islander persons (51.4%) (Characteristics of TB Cases in GENType Clusters by Alert Levels: 2018–2020).
  • Hispanic or Latino persons (n=1,230) and non-Hispanic Black or African American persons (n=958) represented the highest number of clustered cases.

The number of county-based clusters declined from 1,351 in last year’s report (cases reported nationally during 2017–2019) to 1,280 clusters for 2018–2020, a 5.3% reduction.

Genotype Cluster Alert Levels

Genotype clusters are additionally characterized into an alert level of non-alert, medium alert, or high alert based on a log-likelihood ratio calculation. Alert levels represent the degree of spatial concentration of cases within the same county or county-equivalent area as compared with the concentration of the genotype in the nation.

Learn more in the Executive Commentary.