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.