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Technical Notes

National Tuberculosis Surveillance System

Reporting areas (i.e., the 50 U.S. states, the District of Columbia, New York City, Puerto Rico, and other U.S.-affiliated jurisdictions in the Pacific Ocean and Caribbean Sea) provide information about tuberculosis (TB) cases to the Center’s Disease Control and Prevention’s (CDC) National Tuberculosis Surveillance System (NTSS) by using a standard case report form, the Report of Verified Case of Tuberculosis (RVCT). TB cases are verified according to the TB case definition for public health surveillance (Appendix A). TB cases are reported and counted according to the recommendations for reporting and counting TB cases (Appendix B).

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TB Case Definition

In 2009, the TB case definition was modified. TB cases are verified according to the following specified laboratory and clinical criteria (Appendix A).

Laboratory Criteria for Diagnosis

A TB case may be verified by the laboratory case definition with ≥1 of the following criteria: (1) isolation of Mycobacterium tuberculosis complex from a clinical specimen; or (2) demonstration of M. tuberculosis complex from a clinical specimen by nucleic acid amplification test (NAAT), or (3) demonstration of acid-fast bacilli (AFB) in a clinical specimen when a culture has not been or cannot be obtained or is falsely negative or contaminated.

Clinical Case Criteria

A TB case may be verified by the clinical case definition in the presence of all of the following clinical criteria: (1) a positive tuberculin skin test (TST) result or positive interferon-gamma release assay (IGRA) result for M. tuberculosis complex; and (2) other signs and symptoms compatible with TB (e.g., abnormal chest radiograph, abnormal chest computerized tomography [CT] scan, or other chest imaging study or clinical evidence of current disease); and (3) treatment with ≥2 anti-TB drugs; and (4) a completed diagnostic evaluation.

Provider Diagnosis

Provider diagnosis is not a component of the case definition for TB as described in Appendix A. However, when cases of TB are diagnosed but do not meet either the clinical or laboratory case definition, reporting areas have the option of verifying TB cases on the basis of provider diagnosis as described in Appendix B. Through 2008, the RVCT did not collect information about IGRA results. If an IGRA was performed in lieu of a TST, the RVCT would have indicated that a TST was not performed. Thus, culture- and smear-negative cases without a TST that were diagnosed by a positive IGRA result before 2008 were considered to have been confirmed by provider diagnosis. Starting in 2009, positive results for an IGRA have been included as part of the clinical case definition for TB confirmation. Anergic patients with a clinical presentation consistent with TB but without laboratory evidence of M. tuberculosis complex would also be an example of provider diagnosis and one that has not changed over time.

TB Case Verification Criteria Calculation

The software for TB surveillance developed by CDC includes a calculated variable for TB case verification called “VERCRIT,” which was modified in 2009. The new variables, NAAT result, IGRA for Mycobacterium tuberculosis complex at diagnosis, and initial chest CT scan or other chest imaging study were added to the VERCRIT calculation.

VERCRIT is calculated by using the following criteria in hierarchical order:

1. positive culture,
2. positive NAAT,
3. positive AFB,
4. clinical case confirmation, or
5. provider diagnosis.

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Reporting and Counting of TB Cases

In 2009, the recommendations for reporting and counting of TB cases (Appendix B) were modified. TB cases that are verified but not countable for morbidity statistics are now reported to CDC as a measure of programmatic and case management burden. However, data for noncountable TB cases are incomplete and are not included in this report.

The recommendations for counting TB cases among immigrants, refugees, and foreign visitors were revised on the basis of the 2007 recommendations in the Technical Instructions for TB Screening and Treatment for Panel Physicians¹.  Regardless of panel physician classification or citizenship status, immigrants and refugees examined after arriving in the United States and receiving a diagnosis of clinically active TB requiring anti-TB medications should be reported and counted by the locality of their residence at the time of diagnosis. Foreign visitors with diagnosed TB receiving anti-TB therapy and planning to remain in the United States for ≥90 days should be reported and counted by the locality of their current residence.

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RVCT Variables

Data regarding demographic characteristics, clinical or laboratory diagnosis, initial treatment, and treatment outcomes are collected through three RVCT report forms:

1. RVCT form — used for all patients with a verified TB case.
2. Initial Drug Susceptibility Report (Follow-Up Report 1) — used for all patients who had a culture that was positive for M. tuberculosis complex.
3. Case Completion Report (Follow-Up Report 2) — used for all patients who were alive at diagnosis.

The instructions for completing the RVCT forms and the definitions for all data items are available in CDC’s RVCT instruction manual.^{2pdf icon}

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Tabulation and Presentation of TB Data

This report presents summary data for TB cases counted by reporting areas through the end of 2018. TB cases are tabulated by year in which the reporting area verified that the patient had TB and included the patient in its official annual TB case count. Since 2004, the published report has reflected updated information about the numbers of confirmed TB cases for each year from 1993 onward. U.S. totals include data from the 50 states and DC.

Trend data are presented in Tables 1–18. Age-group tabulations are based on the patient’s age during the month and year the patient was reported to the health department as having a suspected TB case. State or metropolitan area tabulations are based on the patient’s reported residence.

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Rates

Rates are expressed as the number of cases reported each calendar year per 100,000 persons. Population denominators used in calculating TB rates were based on official census and midyear postcensal estimates from the U.S. Census Bureau. In Tables 1, 28, and 29, the U.S. total populations for 1990–1999 were taken from the Bridged-Race Intercensal Population Estimates for July 1, 1990–July 1, 1999³; populations for 2000–2009 were taken from the U.S. Census Intercensal Estimates of the Resident Population for the United States, Regions, States, and Puerto Rico for April 1, 2000–July 1, 2010⁴external icon; and populations for 2010–2018 were taken from the U.S. Census Annual Estimates of the Resident Population for the United States, Regions, States, and Puerto Rico: April 1, 2010–July 1, 2018⁵external icon. Beginning in 2004, nonrounded numbers were applied to calculate the annual percentage change in the TB case rate.

During 2003, 2 modifications were made to the RVCT form: (1) multiple race entries (≥2 races reported for a person) were allowed, and (2) the previous category of “Asian/Pacific Islander” was divided into “Asian” and “Native Hawaiian/Other Pacific Islander.” To calculate rates for Tables 2 and 4, denominators for 1993–1999 were obtained from the U.S. Census Monthly Postcensal Resident Population, by single year of age, sex, race, and Hispanic origin⁶external icon. For 2000–2009, denominators for Table 2 were obtained from U.S. Census Intercensal Estimates of the Resident Population by Sex, Race, and Hispanic Origin for the United States: April 1, 2000–July 1, 2010⁷external icon, and denominators for Table 4 were obtained from Intercensal Estimates of the Resident Population by Single Year of Age and Sex for States and the United States: April 1, 2000–July 1, 2010⁷external icon. For 2010–2018, denominators for Table 2 were obtained from the U.S. Census Annual Estimates of the Resident Population by Sex, Race, and Hispanic Origin: April 1, 2010–July 1, 2018⁸external icon, and denominators for Table 4 were obtained from U.S. Census Annual Estimates of the Resident Population for Selected Age Groups by Sex: April 1, 2010–July 1, 2018⁸external icon.

The population source for nativity is the Current Population Survey, which is used to calculate case rates for U.S.-born and non-U.S.–born persons with diagnosed TB. U.S.-born populations include persons born in the 50 states and DC, those born abroad to U.S. parents, and those born in U.S. territories. In Table 5, the populations for U.S.-born and non-U.S.–born persons for 1993 were obtained from Quarterly Estimates of the United States Foreign-born and Native Resident Populations: April 1, 1990–July 1, 1999⁹txt iconexternal icon. Denominators for computing the 1994–2018 rates were based on extrapolations from the U.S. Census Current Population Survey through DataFerrett (U.S. Census Bureau, Washington, DC)¹⁰external icon. Denominators for computing 2018 rates in Table 20 were obtained from U.S. Census Annual Estimates of the Resident Population by Sex, Age, Race, and Hispanic Origin: April 1, 2010–July 1, 2018⁸external icon.

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Rates by Country of Birth

To calculate U.S. TB rates by country of birth for Table 6B, the average annual number of cases by country of birth reported to NTSS during 2014–2018 were used in the numerator. U.S. population estimates by country of birth were used for the denominator and were obtained from the U.S. Census Bureau, American Community Survey (ACS) Public Use Microdata Sample data, 2013–2017, 5-year file¹¹external icon. At the time of this report, the 2014–2018 data had not been published. In ACS, country of birth is self-reported, and persons born outside the United States are asked to report country of birth on the basis of current international boundaries. Population estimates of persons from countries with ≥10,000 persons living in the United States are coded as a country. Population estimates of persons from countries with <10,000 persons living in the United States are coded with a region. When applicable, TB case data were aggregated into regions by using the same regions categorized by ACS, and the TB rate calculated for the region was applied to all countries included in that region¹²external icon.

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Mortality Data

The annual mortality rate is calculated as the number of deaths caused by TB in that year, divided by the estimated population for the year, multiplied by 100,000 (Table 1). The number of deaths was obtained from CDC’s National Center for Health Statistics, Multiple Cause of Death Files, 1999–2017¹³, available from CDC’s WONDER online database. Data were compiled from the 57 vital statistics jurisdictions through the Vital Statistics Cooperative Program¹⁴. Finalized 2018 TB-related death data were unavailable at the time of publication.

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Drug Resistance

Drug-resistance patterns are displayed in separate tables with drug-resistance trend data by previous TB status and origin of birth. Isoniazid resistance and multidrug resistance are displayed in Tables 8 and 9, respectively.

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Completion of TB Therapy

Tables 10, 51, and 52 present percentages of completion of TB therapy (COT). Data collected by RVCT Follow-Up Report-2 forms regarding date and reason therapy was stopped (e.g., the patient completed therapy, or the patient died) were used to calculate COT percentages. Cases were stratified by the indicated length of therapy, based on American Thoracic Society, CDC, and Infectious Diseases Society of America treatment guidelines in effect during the period covered and the patient’s initial drug-susceptibility test results, age, and disease site¹⁵.

In Table 51, the first column lists the total number of cases reported during 2016. The remaining columns are grouped under 2 headings: therapy lasting ≤1 year indicated and therapy lasting >1 year indicated. To be counted in the data presented here, patients eligible to complete therapy in ≤1 year were alive at time of diagnosis and had to have initiated therapy with ≥1 drug. Eligible patients did not have rifampin resistance; did not die in ≤1 year after initiating therapy; did not move out of the country in ≤1 year after initiating therapy; and did not have meningeal TB, bone or joint TB, or TB of the central nervous system, regardless of age. Additionally, TB patients aged 0–14 years were ineligible to complete therapy in ≤1 year if they had disseminated disease (defined as miliary TB, a positive TB blood culture, or a positive NAAT on a blood specimen). Patients with culture-negative disease, those with an unknown culture status, and those with culture-positive disease but unknown initial drug-susceptibility test results were included under the category of therapy of ≤1 year indicated.

For the group with an indicated length of therapy of ≤1 year, percentages are displayed for both COT in ≤1 year and for COT regardless of duration (i.e., duration of therapy ≤1 year or >1 year). For COT ≤1 year, the numerator included only those patients completing therapy in ≤366 days (based on the dates therapy was started and stopped). Patients with missing dates were classified as “treatment not completed” for this calculation.

COT percentages, regardless of duration, were calculated by dividing the number of patients reported as having completed therapy by the number of total eligible patients. Patients with an outcome other than completed therapy (i.e., moved, lost to follow-up, refused treatment, or other) were classified as “treatment not completed.” Patients with an unknown outcome were also classified as “treatment not completed.” For the group of indicated therapy length >1 year, only COT percentages regardless of duration are presented. Table 10 provides percentages for COT ≤1 year and for COT regardless of duration for the group with an indicated therapy of ≤1 year only.

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TB Disease Site

Miliary disease should be reported as a pulmonary form of TB (Tables 7 and 34). Beginning in 2009, miliary disease could not be classified as a TB disease site because it is a clinical or a radiologic finding and should be recorded under Initial Chest Radiograph, Initial Chest CT Scan, or Other Chest Imaging Study. During 1997–2008, miliary disease was classified as both an extrapulmonary and a pulmonary form of TB. In publications before 1997, miliary disease was classified as extrapulmonary TB, unless pulmonary disease was reported as the major disease site.

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Reporting of HIV Status

Information about HIV status for persons with TB is displayed in Tables 11 and 46 for those persons not dead at diagnosis. Table 11 also lists trend data for persons aged 25–44 years. Reporting completeness for HIV status was 92% of TB patients tested among persons aged 25–44 years during 2018; however, this variable is still underreported across jurisdictions. Data regarding the HIV-infection status of persons reported with TB should be interpreted with caution because these data are not representative of all TB patients with HIV infection. TB patients who are tested anonymously for HIV might choose not to share their testing results with their health care provider. TB patients managed in the private sector can receive confidential HIV testing, but results might not be reported to the health department’s TB program. Additionally, certain factors can influence HIV testing among TB patients, including the extent to which testing is targeted or routinely offered to specific groups (e.g., males aged 25–44 years, injection-drug users, or persons experiencing homelessness) and the availability of and access to HIV testing services. These data might overrepresent or underrepresent the proportion of TB patients known to be HIV-infected in a reporting area.

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Primary Occupation for the Past Year

Table 43 reflects the modified 2009 RVCT variable, Primary Occupation Within the Past Year, which replaces the Occupation Within Past 24 Months of TB Diagnosis in previous reports. After the 2009 RVCT revision, Multiple Occupation was removed, and the Retired and the Not Seeking Employment categories were added.

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Reason Therapy Was Stopped

Tables 12 and 49 now include a patient’s adverse reaction to anti-TB drug therapy as an option for the reason therapy was stopped. The 2009 RVCT revision removed the option of Moved as a valid response to the variable Reason Therapy Stopped, and this option is therefore not reported after 2009. Those cases entered as Moved as reason therapy was stopped after 2009 are now categorized as Unknown.

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Metropolitan Statistical Areas

Tables 53, 54, 55, and 56 present data by metropolitan statistical areas (MSAs) having an estimated 2018 population of ≥500,000 persons. MSAs are defined by the White House Office of Management and Budget (OMB), and the definitions are based on the application of the 2010 OMB standards for delineating MSAs to U.S. Census Bureau population estimates¹⁶external icon.

The MSA definitions apply to all areas except the 6 New England states; those states are referred to collectively as the New England County Metropolitan Areas (NECMAs). MSAs are named for a central city in the MSA or NECMA, can include multiple cities and counties, and can cross state boundaries. For example, the TB cases and case rates presented for DC in Table 28 include only persons residing within DC’s geographic boundaries. However, the TB cases and case rates for the Washington, DC-MSA (Table 53) include persons residing within the multiple counties in the metropolitan area, including counties in Maryland, Virginia, and West Virginia. Cities or MSAs with incomplete or unavailable data were not included in the tables, and certain cities’ or MSAs’ total numbers might be underreported because of missing information.

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National TB Genotyping Service

National TB Genotyping Service laboratories primarily use two genotyping methods: spoligotyping and MIRU–VNTR (mycobacterial interspersed repetitive units–variable number of tandem repeats). Both methods require only a minor amount of culture material and provide digital results; using either of these methods provides relatively fast results. All isolates are prepared for long-term storage at genotyping laboratories or CDC.

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TB Genotyping Information Management System

In March 2010, CDC launched the TB Genotyping Information Management System (TB GIMS) as a secure Internet-based system for supporting ongoing use of TB genotyping data in TB control activities. TB GIMS facilitates systematic data collection of TB genotyping results, and it integrates genotyping results with epidemiologic data collected by NTSS to form a national and centralized database. Primary users of TB GIMS include TB laboratories that submit isolates for genotyping; national CDC-contracted genotyping laboratories; state, local, and tribal TB control programs; and CDC programs that apply this information for TB control activities.

Genotyping results from the national genotyping laboratories or CDC are uploaded into TB GIMS as they become available. Line-listed data from the NTSS are also uploaded into TB GIMS weekly. After genotyping results have been linked to individual patient surveillance data in TB GIMS, the record is considered complete. These complete records are essential for the majority of the applications of TB genotyping, including all reports and maps as well as for using the outbreak detection system to identify potential chains of transmission and outbreaks. Thirty system updates have occurred for adding new reports, data management functions, and other tools since TB GIMS was released in March 2010. As of July 2019, 576 users were registered to access the system.

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Genotype Clustering

A genotype cluster comprises ≥2 cases in a jurisdiction during a specified period with each having M. tuberculosis complex isolates that share matching genotypes. The jurisdiction and period used vary on the basis of the specific application. Cases that are part of the same genotype cluster are likely to be related by TB transmission in some way; however, the cases might not be directly related (i.e., 1 person did not necessarily transmit M. tuberculosis to another person in the cluster) or recently related (i.e., both persons might have contracted TB from the same person, but the exposure might have happened years ago). In TB GIMS, clustering is defined as ≥2 cases with matching genotypes (spoligotype and 24-locus MIRU-VNTR) in a single county within a 3-year period.

Mycobacterium bovis

For culture-confirmed TB cases that have been genotyped, Mycobacterium bovis can be defined primarily on the basis of spoligotyping results. The genotype-based definition for M. bovis requires either (1) the absence of spoligotyping spacers 3, 9, 16, and 39–43; the presence of ≥1 of the spacers 29–32; and the presence of ≥1 of the spacers 33–36; or (2) the absence of spacers 3, 9, 16, and 39–43 and ≥2 copies of the repeated sequence at MIRU locus 24; or (3) determination based on microbiologic expertise. Data reported for 2004–2018 exclude cases of bacillus Calmette-Guérin M. bovis, which were defined as spoligotype 676773777777600 with x, y, or z in the second MIRU position. Although cases of bacillus Calmette-Guérin M. bovis were reported during 2004–2018, they are excluded from this report.

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Recent Transmission

Estimates are based on a plausible source-case method that is described in detail elsewhere¹⁷external icon. Briefly, a given case is designated as attributed to recent transmission if a plausible source case with the following five characteristics can be identified in the national surveillance data: the same M. tuberculosis complex genotype, an infectious form of TB disease, patient’s residential location ≤10 miles of the plausible source case, patient’s age ≥10 years, and a diagnosis for the plausible source case ≤2 years before the given case. These criteria were field-validated by using local epidemiologic assessments of whether 1,188 cases in 3 states were actually caused by recent transmission that was attributed to source cases reported during 1996–2000. Any given case with a plausible source case identified is included regardless of cluster size. Among cases attributed to recent transmission, a given case can also be attributed to extensive recent transmission if a plausible chain of transmission of ≥6 cases is identified, including the plausible source case and ≥ 4 other cases ≤ 3 years before a given case in the chain.