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2018 State and City TB Report										Related Pages
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Estimates of Recent Transmission
geographically and in time (dotted circle).Figure 1. Illustration of the plausible-source case method
Control of TB transmission is accomplished through prompt detection and treatment of patients with infectious TB disease, administrative controls designed to reduce exposure to persons with infectious TB, and contact investigations to identify exposed persons at risk for LTBI (i.e., candidates for latent TB infection (LTBI) testing and treatment). Many clinical, epidemiologic, and social factors can make these activities challenging to implement successfully. National estimates of recent transmission for cases reported during 2017–2018 provide a starting place within programs to understand better the populations affected by recent TB transmission and monitor trends over time in TB control.  However, findings from local investigations of clusters and outbreaks, using whole-genome sequencing (WGS)pdf icon results when available, are preferable because estimates of recent transmission rely on surveillance data and are limited by the molecular resolution of genotyping.
Each TB case attributed to recent transmission is further categorized as attributed to extensive recent transmission if the case belongs to a plausible transmission chain of six or more cases with at least five preceding cases in the chain within the previous three yearsFigure 2. Illustration demonstrating how cases are categorized as attributed to extensive or limited recent transmission
Using national molecular surveillance data, CDC attributes a TB case to recent transmission if a plausible source case1 can be identified in a person who has the same *M. tuberculosis* genotype, has an infectious form of TB disease, is at least 10 years of age, resides within 10 miles of the given TB case, and was diagnosed within 2 years before the given TB case. For example, the given case in the center of “Figure 1. Illustration of the plausible-source case method” has two plausible source cases (represented with arrows). The plausible source cases have the same genotype (matching colors), are at least 10 years old (larger), have infectious forms of TB (lungs), and are proximal geographically and in time (dotted circle).
Figure13Figure 13: Percentage of TB Cases Attributed to Recent Transmission, United States, 2017–2018
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CloseFigure13Figure 13: Percentage of TB Cases Attributed to Recent Transmission, United States, 2017–2018
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Each TB case attributed to recent transmission is further categorized as attributed to extensive recent transmission if the case belongs to a plausible transmission chain of six or more cases with at least five preceding cases in the chain within the previous three years. Otherwise, the case is categorized as attributed to limited recent transmission. For example, case 1 in “Figure 2. Illustration demonstrating how cases are categorized as attributed to extensive or limited recent transmission” is a plausible source case, but not attributed to recent transmission. Cases 2–5 are attributed to limited recent transmission, and cases 6–8 are attributed to extensive recent transmission.
For 2017–2018, 3 states and 2 cities with 1–51 TB cases reported in 2018 had percentages of TB cases attributed to recent transmission that were above the national estimate (12.6%); these percentages should be interpreted with caution because small denominators can create unstable estimates (Figure 13image icon, Footnotes). Nine states and one city with 52–139 reported cases, and 4 states and 4 cities with 140 or more reported cases, were above 12.6%. The relative amounts of limited and extensive recent transmission varied substantially.  Because not only TB incidence but also demographics and molecular epidemiology vary considerably among states, counties, and cities, these data should not be compared across jurisdictions.
Additional information on estimates of recent transmission and their limitations can be found in CDC’s Reported Tuberculosis in the United States, 2018.
****Footnotes1France AM, Grant J, Kammerer JS, Navin TR. A field-validated approach using surveillance and genotyping data to estimate tuberculosis attributable to recent transmission in the United States. *Am J Epidemiol* 2015; 182: 799–807.
**Figure 13.  Percentage of TB Cases Attributed to Recent Transmission, United States, 2017–2018***
*This horizontal bar graph shows the percentages of TB cases attributed to recent transmission by individual states and cities in the United States during 2017–2018. The fraction in each parenthesis reports the number of cases attributed to recent transmission out of all genotyped cases that are eligible to be evaluated for recent transmission (i.e., complete data for the plausible-source case method’s algorithm). States and cities are categorized into three groups based on numbers of TB cases reported in 2018 and are ordered by increasing percentage of cases attributed to recent transmission. Dark and light bars show qualitatively the relative proportions of genotyped cases that were attributed to extensive and limited recent transmission, respectively. The total length of the bar represents all recent transmission (i.e., the percentage sums of extensive recent transmission and limited recent transmission equal all recent transmission). During 2017–2018, 12.6% of genotyped cases were attributed to recent transmission in the United States. To understand better the populations affected by recent TB transmission and monitor trends over time in its control, findings from local investigation of clusters and outbreaks, using WGS results when available, are preferable because estimates of recent transmission rely on surveillance data and are limited by the molecular resolution of genotyping. Because not only TB incidence but also demographics and molecular epidemiology vary considerably among states, counties, and cities, these data should not be compared across jurisdictions.
*Data sources: National Tuberculosis Surveillance System and National Tuberculosis Genotyping Service as of June 6, 2019.*
							
					
						Page last reviewed:  March 10, 2020					Content source: 	Division of Tuberculosis Elimination, National Center for HIV, Viral Hepatitis, STD, and TB Prevention, Centers for Disease Control and Prevention homeTuberculosisBasic TB Factsplus iconHow TB SpreadsLatent TB Infection and TB DiseaseSigns & SymptomsTB Risk FactorsExposure to TBTB PreventionVaccinesTB & HIV CoinfectionTB and DiabetesTB TermsPersonal StoriesTesting & Diagnosisplus iconWho Should be TestedTesting for TB InfectionTesting in BCG-Vaccinated PersonsTB Screening and Testing of Health Care PersonnelTesting During PregnancyDiagnosing latent TB infection and TB diseaseTreatmentplus iconDeciding When to Treat Latent TB InfectionTreatment Regimens for Latent TB Infection (LTBI)Treatment for TB DiseaseAdverse EventsTB Treatment of Persons Living with HIVTB Treatment and PregnancyTB Treatment for ChildrenFrequently Asked QuestionsDrug-Resistant TBResearchplus iconTB Epidemiologic Studies Consortiumplus iconResearch ProjectsPublicationsTB Trials Consortiumplus iconStudy DescriptionsBackgroundBehavioral & Social Science ResearchHealth Care Settingsplus iconTB Infection Control in Health Care SettingsResources for TB Screening and Testing of Health Care Personnelplus iconFrequently Asked QuestionsTB in Specific Populationsplus iconHealth DisparitiesAsian PersonsBlack or African American PersonsHispanic or Latino PersonsChildrenPregnancyCorrectional FacilitiesPeople Experiencing HomelessnessInternational TravelersLaboratory Informationplus iconDrug Susceptibility TestingFalse-Positive Investigation ToolkitInterim Laboratory Biosafety Guidance for XDR  tuberculosis strainsModel Performance Evaluation Program (MPEP)Rapid Molecular Testing to Detect Drug-Resistant TB in the USplus iconExecutive SummaryIntroductionBackground on Tests for Molecular Detection of DRGeneral Considerations and Principles for a Molecular DR Testing ServicePossible Scenarios and Scope of Testing for a Molecular DR Testing ServiceResearch NeedsGeneral Recommendations of the Expert PanelCommunication Plan for the ReportRecommendationsReferencesPanel Members and CDC ParticipantsAppendix 1Appendix 2Appendix 3The Uses of Nucleic Acid Amplification Tests for the Diagnosis of TBplus iconGeneral ConsiderationsGeneral Recommendations of the Expert PanelRecommendations to ACET, CDC, DTBEData & Statisticsplus iconTB Incidence in the United StatesReported TB in the US, 2022 Surveillance Reportplus iconNational DataReporting Area DataRisk FactorsDemographicsTB Treatment and Case OutcomesDrug-Resistant TBMolecular SurveillanceTuberculosis in the United States, 2022 (Slide Set)Archived Surveillance Reports and Slide Sets2021 State and City ReportArchived State and City ReportsProfessional Resources & Toolsplus iconTools for Healthcare ProvidersResources for TB Programsplus iconStrengthening Civil Surgeons’ Capacity to Improve LTBI Surveillance and Outcomes Among Status AdjustersNotice of Funding Opportunity (NOFO)Program EvaluationTB Centers of ExcellenceTB Elimination AllianceTB Genotypingplus iconConventional TB GenotypingWhole Genome SequencingTB GIMSAnalytic ToolsLatent Tuberculosis Infection ResourcesPublications & Productsplus iconPatient and Public MaterialsFact SheetsGuidelinesplus iconControl & EliminationDrug-Resistant TBInfection Control & PreventionLaboratory & GenotypingTB & HIVTB in Specific PopulationsTesting & DiagnosisTreatmentVaccines & ImmunizationsArchived TB GuidelinesGuides & Toolkitsplus iconAggregate ReportsCDC TB Surveillance TrainingCore CurriculumEffective TB Interviewing for Contact InvestigationEthnographic GuidesFalse-Positive Investigation ToolkitForging Partnerships to Eliminate TuberculosisGuide to Application of GenotypingLTBI: A Guide for Primary Health Care ProvidersMantoux Tuberculin Skin Testing ProductsReport of Verified Case of Tuberculosis (RVCT)Self-Study ModulesTB Contact Investigation Interviewing Skills CourseTB eDOT ToolkitUnderstanding the TB Cohort Review ProcessNewslettersplus iconTB Notes, No. 4, 2023TB Notes, No. 3, 2023TB Notes. No. 2, 2023TB Notes. No. 1, 2023TB Notes, No. 4, 2022TB Notes, No. 3, 2022TB Notes, No. 2, 2022TB Notes, No. 1, 2022TB Notes, No. 4, 2021TB Notes, No. 3, 2021TB Notes, No. 2, 2021TB Notes, No. 1, 2021Pamphlets, Brochures, Bookletsplus iconQuestions and AnswersPatient Education SeriesTuberculosis - Get the FactsTuberculosis - The Connection between TB and HIV12-Dose Regimen for Latent TB Infection-Patient Education BrochurePostersplus iconMantoux Tuberculin Skin Test Wall ChartWorld TB DayThink TBStop TBTake on TBReports & Articlesplus iconDTBE Authored Journal ArticlesTuberculosis Laboratory Aggregate ReportsSlide Setsplus iconIntroduction to TuberculosisEpidemiology of Tuberculosis Among Non-U.S.​–Born Persons in the United States, 1993–2016Self-Study Modules on Tuberculosis, 1-5 Slide SetsThe Tuberculosis (TB) in Correctional Settingsplus iconFacilitator GuideIntroduction to TB GenotypingEpidemiology of Tuberculosis in Correctional Facilities, United States, 1993-2017Prevention and Control of Tuberculosis in Correctional and Detention FacilitiesGuidelines for Preventing the Transmission of M. TB in Health care SettingsInvestigation of Contacts of Persons with Infectious TBEpidemiology of Pediatric Tuberculosis in the United StatesTargeted Tuberculosis Testing and Treatment of Latent Tuberculosis InfectionElectronic Tools & ResourcesWeb-Based Courses & Webinarsplus iconTB 101 for Health Care WorkersContent SyndicationInfographicsplus iconSocial Media GraphicsCustomizable Take on TB Infographic with InstructionsEventsWorld TB Dayplus iconU.S. TB ChampionsHistoryFeaturesplus iconTB Risk FactorsTreating Latent TB Infection with Short-Course RegimensWorld Tuberculosis (TB) Day 2021World Tuberculosis (TB) Day 2020Linksplus iconState TB Control OfficesAbout Usplus iconMission Statement and Activitiesplus iconDTBE Strategic PlanNational TB Program ObjectivesOrganization ChartAdvisory Groupsplus iconFederal TB Task Force To receive email updates about this page, enter your email address: Email Address			What's this?				Submit


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