Editor’s note: This story and headline were corrected on May 4 because they mischaracterized the difference in outbreak numbers in the two time periods studied. There were 24 outbreaks in the first three-year period and 50 in the following six-year period, for a net decrease of one annual case over the second period. We apologize for the error.
Large tuberculosis (TB) outbreaks in the United States decreased slightly in recent years and disproportionately affected socially and economically vulnerable populations, according to a report last week in Morbidity and Mortality Weekly Report.
Analyzing national surveillance and genomic data, researchers from the Centers for Disease Control and Prevention (CDC) identified 50 large TB outbreaks (defined as 10 or more related cases within a three-year period) across 23 states from 2017 through 2023. Together, the outbreaks accounted for 1,092 of the 61,993 cases reported during that period.
In contrast, there were 24 identified outbreaks from 2014 to 2016, for a net decrease of one case per year from 2017 through 2023. In 2024, the CDC reported six large outbreaks. Nevertheless, the numbers suggest that transmission within family and social networks is an ongoing issue, despite the United States having one of the lowest TB incidence rates in the world.
Large-outbreak cases tied to different demographics
People involved in large outbreaks differed notably from other TB patients. Nearly 80% were US-born, compared with 26% of those with non-outbreak TB. They also had different social and behavioral characteristics. People included in large outbreaks were more likely to report substance use (27% vs 12%), homelessness (9% vs 5%), and incarceration (11% vs 3%).
There were also notable differences in age ranges. Outbreak-associated cases were more common among children 15 years and younger (15% vs 3%) and adults ages 25 to 44 (40% vs 29%). Adults 65 and older were underrepresented in large-outbreak cases (8% vs 26%).
Roughly two thirds of large outbreaks occurred within family or social networks, with transmission occurring in settings such as private residences, social gatherings, and places where substance use occurred. Approximately one quarter of large outbreaks occurred in group settings, including workplaces, correctional facilities, senior care facilities, a university, and a facility for people experiencing homelessness.
Outbreaks were also geographically widespread, occurring in 23 states, including many with TB incidence rates below the national average of 2.6 cases per 100,000 people. From 2017 to 2023, large-outbreak cases accounted for 1.7% of all TB cases.
Genomic surveillance, local programs key to control
Preventing and controlling outbreaks will require national genomic surveillance, write the authors, as well as outbreak-control activities by state and local health programs.
They also emphasize the need for targeted public health strategies focused on populations at increased risk, particularly those experiencing housing instability, substance use, or incarceration. Outbreaks within families or social circles are harder to track and, hence, harder to manage.
Responding to these outbreaks will require building trust with affected communities and partnering with local cultural, religious, and service organizations to identify and treat people at risk, write the authors.
