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Executive Commentary

Introduction

Tuberculosis (TB) is a bacterial disease caused by infection with Mycobacterium tuberculosis complex. Since 1953, the National TB Surveillance System (NTSS) has collected information on each newly reported case of TB disease in the United States. In addition to the 50 United States and the District of Columbia (DC), CDC accepts TB case reports from five U.S. territories (American Samoa, Commonwealth of the Northern Mariana Islands, Guam, Puerto Rico, and the U.S. Virgin Islands) and three sovereign nations that have signed compacts of free association with the United States (Federated States of Micronesia, Republic of the Marshall Islands, and Republic of Palau); however, the information presented in this commentary is based on the case reports from the 50 states and DC, except where otherwise specified. CDC maintains TB surveillance data in an electronic database for all cases reported since 1993; reporting areas may update this information at any time. Small variations in historical data included in this report compared with previous reports are attributed to these updates. This annual summary contains information on TB cases reported to CDC during 1993–2017 by year that the reporting jurisdiction counted the case.

Key Findings

National Level

In 2017, the 50 states and the District of Columbia (herein referred to as the “United States”) reported 9,105 TB cases to CDC, representing the lowest number of annual cases on record and 1.6% decrease from 2016 (Table 1). The national TB incidence rate was 2.8 per 100,000 persons, a 2.3% decrease from 2016 (Table 1).

State, Territorial, and Local Level

California (2,057 cases, 22.6%), Texas (1,127 cases, 12.4%), New York (806 cases, 8.9%), and Florida (549 cases, 6.0%) reported the greatest number of cases in 2017 (Table 29). Together, they accounted for just under half of the cases reported by the 50 states and DC (Table 29). Hawaii (8.1), Alaska (7.2), California (5.2), and DC (5.2) reported the highest incidence rates per 100,000 persons (Table 28). Twelve states and DC reported incidence rates above the national average of 2.8 cases per 100,000 persons (Table 28). While case counts were comparatively low in the U.S. territories and freely associated states, reported incidence rates per 100,000 persons ranged from zero in the U.S. Virgin Islands to 352.8 in the Republic of the Marshall Islands (Table 28).

Among Metropolitan Statistical Areas (MSA) with ≥500,000 population in 2017, the New York-Newark-Jersey City MSA reported the greatest number of cases (976), followed by Los Angeles-Long Beach-Anaheim (726 cases), San Francisco-Oakland-Hayward (357 cases), and Houston-The Woodlands-Sugar Land (341 cases) (Table 53). However, San Jose-Sunnyvale-Santa Clara (9.3), Urban Honolulu (9.1), San Francisco-Oakland-Hayward (7.6) and San Diego-Carlsbad (7.1) reported the highest incidence rates per 100,000 persons (Table 53).

Demographic Characteristics

Country of Birth

Country of birth continues to be a major risk factor for TB diagnosed in the United States because the risk of TB exposure varies by country. In 2017, 2,705 TB cases were reported in U.S.-born persons (defined as persons born in the United States or its territories, or born elsewhere to a U.S. citizen parent), compared with 6,384 cases in non-U.S.–born persons (29.7% vs 70.1%) (Table 5). In terms of incidence rates per 100,000 persons, U.S.-born persons had a TB rate of 1.0 compared with 14.7 among non-U.S.–born persons (Table 5). Among non-U.S.–born persons reported with TB in 2017, the top five countries of birth by number of cases reported were Mexico, the Philippines, India, Vietnam, and China (Table 6).

Among the cases reported in non-U.S.–born persons in 2017, a total of 1040 (16.3%) were diagnosed <1 year after first arrival in the United States, which is consistent with previous observations of the proportion of TB cases among non-U.S.–born persons diagnosed in the first few years after arrival in the United States (Table 19). Approximately equal percentages of TB cases among non-U.S.–born persons occurred <10 years and ≥10 years after first arrival, demonstrating that TB is a concern among all non-U.S.–born persons, even long-term U.S. residents (Table 19).

Race and Ethnicity

TB continues to affect racial and ethnic minorities disproportionately compared with non-Hispanic whites. The TB incidence rate per 100,000 persons for non-Hispanic whites has remained relatively stable for the past 4 years and is currently 0.5, while the incidence rate for other racial/ethnic groups in 2017 ranged from 3.9 for non-Hispanic American Indians/Alaska Natives to 19.1 among non-Hispanic Native Hawaiians/Other Pacific Islanders (7.2–35.2 times the rate for non-Hispanic whites) (Table 2).

Among U.S.-born persons reported with TB disease in 2017, non-Hispanic blacks were most commonly represented (1,007 cases, 37.2%), followed by non-Hispanic whites (803 cases, 29.7%) and Hispanics (593 cases, 21.9%) (Table 3). Among non-U.S.–born persons reported with TB disease in 2017, non-Hispanic Asians (3,115 cases, 48.8%) were the largest group, followed by Hispanics (1,967 cases, 30.8%) and non-Hispanic blacks (900 cases, 14.1%) (Table 3).

Age

TB remains most commonly reported among persons 25–64 years of age (60.6%), followed by older adults (≥65 years of age) at 25.3% and adolescents and young adults between 15 and 24 years of age at 9.3% (Table 4). Children <15 years of age constitute only 4.7% of U.S. TB cases, although these cases are often of great concern to TB programs as they might be indicators of recent transmission of TB (Table 4).

Clinical Characteristics

Site of Disease

Pulmonary disease (either exclusively or in combination with extrapulmonary disease) continues to represent the vast majority (79.2%) of U.S. TB cases (Table 7). Among the 1,887 cases reported with exclusively extrapulmonary disease, the most commons sites of disease included the lymphatic system (37.8%), the pleura (15.6%), bones or joints (9.2%), the peritoneum (5.9%), the meninges (4.3%), and the genitourinary system (4.1%) (Table 15). Of note, there were no laryngeal (a particularly infectious site of TB disease) TB cases reported in 2017 (Table 15).

Case Verification Criteria

The vast majority (78.1%) of U.S. TB cases were confirmed via microbiologic culture that isolated M. tuberculosis complex from a clinical specimen, while 2.9% did not have a positive culture result but were confirmed either through a positive nucleic acid amplification test conducted directly on a clinical specimen or on the basis of identification of acid-fast bacilli through microscopic examination of a clinical specimen (Table 7). The remaining 19% of cases, which were not verified through microbiologic testing, were confirmed either by meeting clinical criteria or on the basis of a diagnosis made by a healthcare provider (Table 7).

Comorbidities

Among persons reported with TB in 2017, a total of 439 (5.5% of TB cases with test result information) were co-infected with HIV (Table 11). Of these patients with HIV/TB coinfection, 236 were 25–44 years of age (9.2% of TB cases in this age group with test result information) (Table 11). The percentage of HIV/TB co-infection has remained stable over the last 3 years (Table 11). Additionally, diabetes mellitus continues to be an important clinical risk factor for TB disease. In 2017, a total of 1,816 (19.9%) persons reported with TB also had diabetes (Table 35). Immunosuppressive conditions other than HIV were reported in 650 (7.1%) of 2017 TB cases and 708 (7.8%) cases occurred in persons who were a known contact of an infectious TB case (Table 35).

Social and Behavioral Risk Factors

Congregate Settings

Residence in congregate settings remains a risk factor for TB infection, which can subsequently progress to TB disease. Additionally, TB cases in congregate settings increase the risk of secondary cases and the difficulty of subsequent contact investigations. Among TB cases reported among persons ≥15 years of age in 2017, healthcare providers diagnosed 268 (3.1%) cases among residents of correctional facilities (Table 37), 397 (4.6%) cases in persons who experienced homelessness in the year preceding diagnosis (Table 38), and 150 (1.7%) cases among residents of long-term care facilities (Table 39).

Substance Use

Substance use is also a risk factor for TB infection and for progression to TB disease. Among TB cases diagnosed in persons ≥15 years of age that were reported in 2017 with information on history of substance use in the year preceding TB diagnosis, 101 (1.2%) cases were among persons who reported injecting drugs (Table 40), 573 (6.7%) reported using noninjectable drugs (Table 41), and 753 (8.9%) reported excessive alcohol use (Table 42).

TB Drug Resistance

Isoniazid Resistance

Resistance to anti-TB drugs remains relatively low in the United States, with 598 (9.2%) cases among all cases with available information on anti-TB drug susceptibility, previous history of TB, and origin of birth being resistant to at least isoniazid in 2017 (Table 8). While the proportion of cases with no previous history of TB disease that reported isoniazid resistance (i.e., primary isoniazid resistance) has remained stable at approximately 9% in the last several years, the proportion of cases with at least one previous episode of TB disease that reported isoniazid resistance (i.e., potentially acquired isoniazid resistance) has been increasing in recent years to nearly 20% (Table 8).

Multidrug Resistance (MDR)

The percentage of U.S. TB cases that are multidrug-resistant (MDR, or resistant to at least isoniazid and rifampin) TB has remained steady for >20 years at approximately 1% of culture-positive cases with drug susceptibility results (Table 9). The United States reported two extensively drug-resistant TB (defined as MDR TB that is additionally resistant to any fluoroquinolone and at least one of three injectable second-line anti-TB drugs) cases in 2017.

TB Treatment and Outcome

Initial Treatment Regimen

To reduce the risk of inducing drug resistance, CDC recommends treating all newly diagnosed TB cases with at least four anti-TB drugs.¹ The typical initial drug regimen for TB cases not known to have drug resistance includes isoniazid, rifampin, pyrazinamide, and ethambutol (i.e., IRZE regimen). In 2017, 83.2% of U.S. TB cases received the recommended IRZE regimen as the initial drug regimen (Table 10). An additional 10.2% of cases received a different initial drug regimen that still included at least four anti-TB drugs (Table 10).

Directly Observed Therapy (DOT)

CDC recommends the use of DOT for treatment of TB patients whenever possible.¹ Among cases reported in 2015, the most recent year for which case completion data are available, 65.1% of TB patients received DOT exclusively and an additional 28.5% of patients received a combination of DOT and self-administered therapy. These percentages have been stable since 2011 (Table 10). Many TB programs are exploring alternatives to traditional DOT, such as the use of videoconferencing or other electronic means of monitoring medication adherence; however, NTSS does not currently distinguish these alternative strategies from traditional DOT.

Completion of Treatment

Among patients expected to complete TB treatment within 1 year of diagnosis, 89.5% completed therapy within 1 year (Table 10). An additional 6.3% (total of 95.8%) of these individuals eventually completed treatment (Table 10). Among persons with TB reported in 2015, a total of 8,133 (87.6%) completed treatment, 572 (6.2%) died before completing treatment, and the remainder discontinued treatment for other reasons (Table 12).

Among TB cases reported in 2015, a total of 792 (8.7%) died either before treatment could be started, or after starting treatment but before completing treatment (Table 13). Among those who died, 281 (35.5%) were reported as having died because of TB disease or the adverse effects of TB treatment (Table 13).

Molecular Surveillance

Genotype Clusters

TB genotyping is a laboratory-based analysis used to characterize a small portion of the genetic material of bacteria belonging to the M. tuberculosis complex. TB genotype clusters are defined in this report as ≥2 cases with matching genotypes in the same county during a 3-year time period. CDC identified clusters among 20.3% of genotyped cases during 2015–2017 (Table 24). Clusters are classified into alert levels based on a log-likelihood ratio (LLR) calculation; clusters with an LLR ≥5 are classified as a medium alert level and clusters with an LLR ≥10 are classified as a high alert level. While not all clustered cases result from recent transmission, clusters with high or medium alert levels could represent TB outbreaks.² During 2015–2017, 17.6% of clustered cases were part of high-alert clusters and 24.3% of clustered cases were part of medium-alert clusters (Table 24).

Estimates of Recent Transmission

This is the second annual TB surveillance report that provides national estimates of recent transmission and extensive recent transmission. CDC attributes a TB case to recent transmission if a plausible source case with a matching genotype is identified within a specified geographic radius and has a diagnosis within 2 years prior to the case (see Estimates of Recent Transmission, 2016–2017 section for more details).³ Nationally, CDC attributed 1,787 (13.1%) of 13,650 genotyped cases reported during 2016–2017 to recent transmission (Table 57, Figure 1). These 1,787 cases are further attributed to extensive recent transmission if a plausible chain of transmission of ≥6 cases, including the plausible source case and 4 or more other cases within 3 years before a given case in the chain, is identified (see Estimates of Recent Transmission, 2016–2017 section).⁴ Nationally, 4.6% of genotyped cases are attributed to extensive recent transmission, although state- and county-level estimates vary considerably (Tables 57 and 58). Forty-seven counties or regions had >5% of their genotyped cases attributed to extensive recent transmission during 2016–2017 (Table 58, Figure 2). Greater proportions of cases attributed to recent transmission and extensive recent transmission were identified among certain racial groups and among persons with social and behavioral risk factors, as compared with national averages (Table 59).

Conclusions

TB remains a serious problem in the United States even though it is both preventable and curable. Persons with TB are in every state, in rural areas and cities, in schools, workplaces, homes, and many other places where people are in close contact.

TB elimination (defined as <1 TB case per 1 million persons) would have widespread health, economic, and social benefits in the United States. The overall number of TB cases and the TB incidence rate in the United States decreased from 2016 to 2017. While the United States continues to make slow progress toward TB elimination, statistical modeling suggests that new and expanded approaches will be required to achieve TB elimination in the United States.^5,6

Several interventions have been proposed to accelerate the decline in U.S. TB incidence, including increasing testing and treatment for latent TB infection (LTBI) in high-risk populations, enhancing detection of TB cases to reduce transmission through the provision of treatment as prevention, and improving TB treatment regimens to increase the proportion of TB cases that successfully complete treatment. An epidemiologic model of each of these potential interventions estimated that increasing screening and treatment for LTBI in high-risk populations would result in the greatest reductions of any single intervention in LTBI prevalence and TB disease incidence.⁶

To this end, CDC has placed additional emphasis on efforts to identify and treat LTBI. Among these efforts are the implementation of case-based sentinel surveillance for LTBI, evaluation of existing data sources (e.g., administrative claims data and electronic health records) for utility in estimating LTBI prevalence, and improvements in LTBI treatment such as the expansion of the recommendation for the short-course isoniazid-rifapentine regimen to be used in persons 2 years of age and older and in persons coinfected with HIV who are able to take rifapentine, as well as for use of the regimen by self-administered therapy or directly observed therapy.⁷