Epidemiology of Tuberculosis in the United States
The incidence of tuberculosis in the United States has substantially decreased since the early 1990s (Figure 1), but cases continue at a significant rate, with 7,882 cases reported in 2021.[1] The case rate is especially high among persons from individuals in correctional facilities, persons experiencing homelessness, persons who use drugs, and individuals with HIV.[1,2] In recent years, most tuberculosis cases in the United States were among persons who were non-United States-born (71% of all cases in 2021), with an incidence rate approximately 16 times higher than among persons born in the United States (Figure 2).[1] Among racial/ethnic groups, rates of tuberculosis in the United States have occurred at the highest rates among persons who are Native Hawaiian/Other Pacific Islander and Asian (Figure 3).[1]
Epidemiology of Tuberculosis in Persons with HIV
In the late 1980s and early 1990s, HIV contributed to the significant increase of tuberculosis in the United States (48% of tuberculosis cases occurred in persons with HIV coinfection in 1993).[3] In the last 10 years, the overall number (Figure 4) and proportion (Figure 5) of tuberculosis cases involving persons who had HIV coinfection has been substantially lower than in the 1990s.[1] For the year 2021, the CDC reported that HIV status was known for approximately 90% of the persons diagnosed with tuberculosis in the United States, and among those with known HIV status, 4.2% had HIV confection; a total of 293 cases of tuberculosis in persons with HIV were identified in 2021.[1] Tuberculosis continues to cause significant morbidity and mortality among people with HIV in the United States.[4]
Progression from Latent to Active TB
The development of tuberculosis can occur in the setting of recent exposure to Mycobacterium tuberculosis (primary or active disease) or with reactivation of latent tuberculosis infection (LTBI).[5,6] The development of tuberculosis disease is based on complex interactions between host immune status and the bacillary load; in persons with HIV, this balance is impacted both by HIV-related immunosuppression and restoration of immune function by antiretroviral therapy (Figure 6).[5] The risk of progression from LTBI to active disease is markedly increased in individuals infected with HIV (3 to 16% per year) compared with those without HIV (5 to 10% lifetime risk).[7,8,9] The increased risk of LTBI reactivation begins soon after acquisition of HIV.[10] Investigators have identified several comorbidities in addition to HIV that contribute to the risk of developing active disease, including diabetes, malnutrition, low body weight, smoking, lung disease, injection drug use, and recent or current use of immunosuppressant medications.[11]
Prevention of Tuberculosis in Persons with HIV
Combination antiretroviral therapy markedly decreases the risk of developing active tuberculosis, with greater declines occurring with more substantial increases in CD4 cell counts and longer duration of antiretroviral therapy.[12] Nevertheless, the risk of incident tuberculosis remains higher among those with HIV compared to those without HIV, even after CD4 recovery on antiretroviral therapy, or initiation of antiretroviral therapy at higher CD4 cell counts.[13] Individuals with HIV who have positive LTBI testing, either tuberculin skin test (TST) or interferon gamma release assay (IGRA), are associated with increased risk of progression to active tuberculosis.[14,15,16,17]