The United States has one of the lowest tuberculosis (TB) rates in the world — but outbreaks still happen. Stopping them depends on quickly diagnosing and treating both TB disease and latent TB infection (LTBI), which has no symptoms but can turn into infectious disease if untreated. Health departments do this work: they treat people with TB disease, usually with at least 4 months of directly observed therapy, and trace contacts so exposed people can be evaluated and treated. When something gets in the way, transmission continues.
In 2014, CDC began national surveillance for large TB outbreaks: 10 or more related cases within 3 years. In 2014–2016 it found 24, with 518 cases, mostly among U.S.-born people, spread in households and social networks. This report covers 2017–2023.
How outbreaks are found
Every U.S. TB case is reported to the National Tuberculosis Surveillance System, and since 2018 CDC has sponsored whole-genome sequencing of TB bacteria from every patient with culture-positive disease. Cases are counted as related if their bacteria differ by five or fewer SNPs — or, without sequencing, if there is an epidemiologic link. An outbreak stays open until two years pass with two or fewer new linked cases. (Two outbreaks caused by contaminated bone graft implants were excluded, as they weren't person-to-person spread.)
What they found
| Large outbreaks | 50, in 23 states — 17 of them with TB rates below the national average of 2.6 per 100,000 |
| Per year | about 7 on average — from 2 in 2020 to 11 in 2018 |
| Cases | 1,092 — median 18 per outbreak (range 10–63); 1.7% of all TB cases in the period |
Large tuberculosis outbreaks by jurisdiction, 2017–2023. CDC
Who was affected
Compared with the 61,993 other people diagnosed with TB in 2017–2023, people in large outbreaks were:
| Large outbreaks | Other TB cases | |
|---|---|---|
| U.S.-born | 79% | 26% |
| Under 15 | 15% | 3% |
| Aged 25–44 | 40% | 29% |
| 65 or older | 8% | 26% |
| U.S.-born American Indian or Alaska Native | 11% | 1% |
| U.S.-born Black | 42% | 9% |
| Non-U.S.-born Asian | 5% | 33% |
| Non-U.S.-born Hispanic | 8% | 24% |
| Substance use | 27% | 12% |
| Homelessness | 9% | 5% |
| Incarceration | 11% | 3% |
| Completed treatment | 92% | 94% |
Clinical features and medical risk factors, including HIV, were similar in both groups.
Contact tracing catches TB earlier
292 (27%) outbreak cases were found through contact tracing. Only 23% of them had signs of advanced, highly infectious disease (positive sputum smears or lung cavities), against 61% of outbreak cases found in other ways — through symptoms, targeted screening or chance findings on x-rays or lab tests. That suggests contact tracing caught people earlier, when they were less infectious, and may have prevented further spread.
Where TB spread
| Primary setting | Outbreaks |
|---|---|
| Family and social networks — often across private homes, community gatherings, places where drugs were used, or unknown settings | 34 (68%) |
| Congregate settings | 13 (26%): workplaces (5), correctional facilities (4), senior care facilities (2), a university (1), a homeless facility (1) |
| Couldn't be determined | 3 (6%) |
What makes outbreaks hard to stop
Congregate settings — where people spend long hours close together, often crowded and poorly ventilated — can spread TB. Regular TB screening, resident rosters and staff and resident education are proven defenses in overnight facilities; one prison outbreak was linked to a lapse in routine TB infection control.
Family and social networks are harder. There are no institutional records to work from, so finding exposed people depends on patients being willing and able to name contacts. Stigma, mistrust of government, involvement in illegal activity, and exposures where people don't exchange names can all get in the way. Building trust — through partnerships with local cultural and religious groups and community service providers — often takes sustained effort.
Substance use and homelessness, more common in these outbreaks, raise the risk of exposure and progression to disease and make follow-up harder: unstable living conditions, reluctance or inability to name contacts, and competing priorities. What helps: mobile testing and treatment, shorter treatment regimens, and incentives and enablers — transportation, housing support, food assistance.
What the authors recommend
- Keep public health capacity for TB outbreak detection and response — even where TB is rare.
- Continue national genomic surveillance, while state and local programs stand ready to scale up during outbreaks.
- Tackle barriers tied to homelessness and substance use, and build trust with affected communities directly and through local partners.
- In congregate settings, keep procedures to promptly identify and isolate people with infectious TB.
Limits: outbreaks are found mainly through genomic data, so those made up largely of clinically diagnosed cases without reported links may be missed; and because most infected people never develop disease and latent infection isn't nationally reported, the true extent of spread is likely underestimated.
Sources
Based on Raz KM, Haddad MB, Althomsons SP, et al., "Large Tuberculosis Outbreaks — United States, 2017–2023," MMWR volume 75, number 16, Centers for Disease Control and Prevention; a work of the United States government in the public domain.
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