Reported Tuberculosis in the United States, 2021

Estimates of Recent Transmission, 2020–2021

Overview

CDC uses genotyping data to estimate the number and percentage of TB cases resulting from recent transmission. TB control programs can monitor trends in recent transmission within their jurisdictions by comparing current state- and county-specific estimates in this section of the annual report with corresponding estimates from previous annual reports. These estimates and their trends over time can facilitate identification of locations or populations within jurisdictions that are disproportionately affected by recent TB transmission and inform assessments of impacts of external events, such as the ongoing COVID-19 pandemic, on recent transmission. In addition, TB control programs can use recent transmission estimates to prioritize interventions toward populations and geographic locations disproportionately affected by recent transmission, regardless of the overall TB incidence.¹ For example, jurisdictions might prioritize resources towards contact investigations and epidemiologic investigations for those populations with more recent transmission and extensive recent transmission. However, these estimates are not intended for comparisons across jurisdictions because of differences in underlying molecular epidemiology and population characteristics between states and counties.

Only culture-confirmed, genotyped TB cases can be attributed to recent transmission or extensive recent transmission (see Technical Notes for a description of the methodology). Recent transmission estimates are displayed within maps in this report as counts of cases attributed to recent TB transmission (Figure 1). Extensive recent transmission estimates are presented as a percentage of all genotyped cases among counties with ≥10 genotyped cases (Figure 2).

Recent Transmission in the United States

In the 50 U.S. states and the District of Columbia, 1,400 (12.3%) of 11,404 genotyped TB cases reported during 2020–2021 were attributed to recent transmission (Table 52). Furthermore, 456 (4.0%) cases were attributed to extensive recent transmission. Estimates of the percentage of cases attributed to recent and extensive recent transmission have remained steady since 2018–2019 (i.e., before COVID-19 emerged) with 1,703 (12.5%) and 557 (4.1%) of genotyped cases attributed to recent transmission and extensive recent transmission, respectively.²

Geography

Stratified by reporting area, percentages of genotyped cases attributed to recent transmission during 2020–2021 ranged 0.0%–43.7%; the percentages of cases attributed to extensive recent transmission ranged 0.0%–25.6% (Table 52). Forty-five reporting areas had at least one case attributed to recent transmission during 2020–2021 compared with 47 during 2018–2019; 27 reporting areas had at least one case attributed to extensive recent transmission during 2018–2019 compared with 29 during 2020–2021 (Table 52).²

Forty-two counties or county equivalents with 10 or more genotyped cases had >5% of cases attributed to extensive recent transmission (median 10.6%; range 5.1%–65.4%) (Table 53) during 2020–2021 which is five fewer counties than during 2018–2019.²

Demographic and Social Characteristics

The percentages of cases attributed to recent transmission and extensive recent transmission during 2020–2021 were higher among U.S.-born persons (24.8% and 8.9%, respectively) than non-U.S.–born persons (7.7% and 2.2%, respectively) (Table 54) and similar to percentages during 2018–2019.² Although 71.4% of reported cases in the United States were among non-U.S.–born persons during 2020–2021 (Table 10), 53.6% of cases attributed to recent transmission and 59.0% of cases attributed to extensive recent transmission were among U.S.-born persons (Table 54). Estimates of recent transmission and extensive recent transmission in children aged 5–14 years were 33.3% and 9.5%, respectively during 2018–2019 compared with 23.1% and 6.8%, respectively during 2020–2021.²

Disparities in estimates of recent transmission and extensive recent transmission among race/ethnicity groups have persisted since before the emergence of COVID-19. Non-Hispanic Native Hawaiian or Other Pacific Islander persons had the largest difference in the percentage of cases attributed to recent and extensive recent transmission (35.4% and 17.1%, respectively) during 2020–2021 compared with 2018–2019 (32.3% and 12.3%, respectively).² Estimates of recent and extensive recent transmission among TB cases occurring in non-Hispanic Asian persons during 2020–2021 were 6.9% and 2.0%, respectively, compared with 7.4% and 2.6% during 2018–2019.² Among TB cases occurring in non-Hispanic White persons, estimates of recent transmission and extensive recent transmission during 2020–2021 were 10.8% and 3.5%, respectively, compared with 12.3% and 3.9% during 2018–2019.²

Among TB cases occurring in persons residing in a correctional facility at the time of TB diagnosis, percentages attributed to recent transmission and extensive recent transmission were higher during 2020–2021 (26.7% and 18.0%, respectively) (Table 54) compared with 2018–2019 (18.1% and 10.4%, respectively).² Although percentages of cases attributed to recent transmission and extensive recent transmission among persons experiencing homelessness also remained higher than the overall national estimates during 2020–2021 (27.1% and 13.0%, respectively) (Table 54), recent transmission estimates have declined and extensive recent transmission estimates are similar when compared with 2018–2019 (30.9% and 13.4%, respectively).² Percentages of cases attributed to recent transmission and extensive recent transmission among cases for which injecting drug use was reported were higher in 2020–2021 (29.9% and 12.6%, respectively) compared with 2018–2019 (27.1% and 9.4%, respectively) (Table 54).²

Application

Recent transmission and extensive recent transmission estimates are intended to be used at the population level rather than for classifying individual cases. As such, these estimates offer state and local TB control programs opportunities for monitoring trends in recent transmission in populations and locations of most concern in their jurisdictions, for assisting in prioritization of public health activities and interventions and assessing the impact of public health emergencies such as COVID-19 on state, local, territorial, and tribal programs.