What to know
A total number of 1,110 tuberculosis (TB) disease clusters were reported nationally in 2021–2023 compared with 987 in 2020–2022. In 2021–2023, as in prior years, percentages of clustered TB disease cases were higher among U.S.-born persons (71.1%) compared with non-U.S.–born persons (54.1%).
Introduction
TB genotyping is a laboratory-based approach used to analyze the DNA of Mycobacterium tuberculosis. Characterizing distinct genetic patterns distinguishes among different TB strains.
This is the second year CDC is reporting whole-genome sequencing-based genotyping results using wgMLSType (whole-genome multilocus sequence type). TB genotyping surveillance coverage is defined as the percentage of TB cases with a laboratory-confirmed test for TB bacteria with a genotype result. In 2023, TB genotyping coverage was 96.0%.
This report considers a TB case clustered if the wgMLSType of the case matches the wgMLSType from other cases in the same county or county-equivalent area during 2021–2023. CDC generates cluster alerts (i.e., medium alert and high alert) based on cases with a matching wgMLSType within the same county or county-equivalent area compared with cases outside of the given county or county-equivalent area. CDC reviews medium and high alerts weekly for possible follow-up with state TB programs. TB programs can use these alerts to help allocate and prioritize resources for investigation and intervention for specific cases.
Key findings
At the cluster level, 52.1% (578) of 1,110 clusters identified nationally during 2021 to 2023 were either medium- (44.7%, 496) or high-level alerts (7.4%, 82).
Overall, 17.4% (3,384 of 19,445 TB cases) of TB disease cases during 2021–2023 were clustered compared with 16.9% (2,999 of 17,694 TB cases) in 2020–2022.
- Among U.S.-born cases, 38.0% (1,758 of 4,632 TB cases) were clustered during 2021–2023 compared with 37.1% (1,673 of 4,509 TB cases) during 2020–2022.
- Among non-U.S.–born cases, 10.9% (1,613 of 14,738 TB cases) were clustered during 2021–2023 compared with 10.0% (1,312 of 13,104 TB cases) during 2020–2022.
Percentages of clustered cases in alerted clusters varied across populations during 2021–2023:
- By racial/ethnic identity, percentages of clustered cases in alerted clusters were highest among American Indian or Alaska Native persons (98.0%, 144 of 147 persons) and lowest among Hispanic or Latino persons (52.5%, 804 of 1,531 persons).
- By age group, percentages of clustered cases in alerted clusters were highest among children aged 5–14 years (78.6%, 70 of 89 persons).
- Among selected risk factors for TB disease, persons who reported injecting drug use (69.6%, 55 of 79 persons) and excess alcohol use (68.9%, 352 of 511 persons) had the highest percentages in alerted clusters.