Base Case
The base case is the default scenario, assuming no change in current TB prevention and control activities. This scenario is automatically included in all visualizations, and other scenarios are defined and analyzed with reference to this scenario.
Dynamic Transmission Model
Dynamic transmission models are systems of mathematical equations designed to reproduce the epidemiology of communicable diseases. These analyses assume that improvements in disease control (such as more rapid diagnosis and treatment of infectious individuals) will reduce the risk that uninfected individuals will be exposed to infection. In this manner, individuals not directly reached by an intervention may still benefit by experiencing a lower risk of infection.
IGRA – Interferon-Gamma Release Assays
IGRAs are blood tests that can aid in the diagnosis of tuberculosis infection.
Incident Cases
Incident cases are new disease cases. Incidence refers to the number of new cases that develop in a particular population in a given period of time.
Isoniazid (INH)
A medicine used to prevent TB disease in people who have latent TB infection. INH is also one of the four medicines often used to treat TB disease.
LTBI – Latent tuberculosis infection
A condition in which individuals are infected with TB bacteria, but this infection is controlled by the individual's immune system. People with latent TB infection have no symptoms, don't feel sick, and can't spread TB to others. Individuals with LTBI usually have a positive TB skin test or positive TB blood test reaction. Individuals with LTBI may develop TB disease in the future if they do not receive treatment.
Prevalence
The number of cases of a disease present in a population at a given time.
QALY – Quality Adjusted Life Year A summary measure of health attainment, which considered both the quality and the quantity of life lived. One QALY is equivalent to a year of life lived in full health.
Rifapentine (RPT)
A medication used to treat latent TB infection.
TST – Tuberculin Skin Test
TSTs determine if someone has developed an immune response to the bacterium that causes tuberculosis, Mycobacterium tuberculosis.
TB – Tuberculosis
A disease caused by bacteria that are spread from person to person through the air. TB usually affects the lungs, but it can also affect other parts of the body, such as the brain, the kidneys, or the spine. In most cases, TB is treatable and curable; however, people with TB disease can die if they do not get proper treatment.
Users of Tabby2 progress through a sequence of pages that provide a brief introduction to the tool, allow them to specify scenarios and choose outcomes of interest, and to view and download graphs of their chosen outcomes. The tool's sidebar (Figure 1) serves as the primary navigational aid for the user.
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Figure 1: Sidebar Showing the Sections of the Tabby2 Application
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On the introduction page of Tabby2 (Figure 2), the user is shown the About Tabby2 text and is prompted to select a location. After specifying a location, Tabby2 will load figures showing historical data and model estimates calibrated to that location.
The Targeted Testing and Treatment (TTT) Interventions input page (Figure 3) is used to create scenarios that simulate additional screening of specific risk groups over a specified number of years. Within the TTT scenario builder, a user can either select from a list of high-risk groups (such as people living with HIV) or choose to define a custom risk group. To do so, the user must define the new group in terms of their rate ratios of LTBI prevalence, progression, and mortality, as compared to the general population in the same age and nativity group. Additionally, a user must provide an age range, nativity group, and total targeted population size.
The Care Cascade Changes page (Figure 4) allows users to change assumptions related to the LTBI treatment and TB treatment care cascades. These changes do not change any historical projections the model has made and will only be active in the years following the user-inputted start year.
The Combination Scenarios page (Figure 5) allows users to simulate combinations of targeted testing and treatment for LTBI, and changes to the care cascade.
Figure 5: User Interface for Building Combination Scenarios
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Model outcomes are presented as five interactive pages with visualizations: Estimates, Time Trends, Age Groups, Counts of Services and Comparison to Recent Data.
The Estimates page provides graphs of modelled results at five major time points: 2020, 2022, 2025, 2035, and 2050.
The Time Trends page (Figure 6) provides graphs of modelled results for each individual year from 2020 to 2050.
The Age Groups page provides graphs of modelled results for a specific year chosen by the user, subdivided into 11 age groups.
The Counts of Services page provides graphs of additional model results for each individual year from 2020 to 2050.
The Comparison to Recent Data page shows model results compared to recent empirical data and estimates.
A detailed description of each of these pages is provided below.
User options are shown in a column on the left. The user specifies:
Comparison: results can be shown as absolute values for each outcome in each year, as a percentage of the base case scenario in the same year, or as a percentage of the base case scenario in 2020.
Subgroup: results can be shown for the total population, or for a subgroup described by nativity (U.S.-born, non-U.S.-born), and broad age groups (0-24 years, 25-64 years, 65+ years).
Outcome: results can be shown for five different outcomes:
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Incident TB infections representing the annual number of incident M. tuberculosis (Mycobacterium tuberculosis) infections per 100,000 due to transmission within the United States (includes reinfection of individuals with prior LTBI, excludes migrants entering the United States with established LTBI);
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LTBI Prevalence representing the percentage of individuals with latent TB infection in a given year;
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TB Incidence representing the annual number of notified TB disease cases per 100,000, including those after death;
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TB-Related Deaths representing annual TB-attributable mortality per 100,000.
Scenarios: results can be shown for up to five scenarios selected by the user, describing hypothetical changes to current TB prevention and control activities ("Modelled Scenarios").
Download: clicking on a button initiates download of the visualization itself (.png, .pdf, .pptx) or the estimates underlying the visualization (.csv, .xlsx).
User options are shown in a column on the left. The user specifies:
Comparison: results can be shown as absolute values for each outcome in each year, as a percentage of the base case scenario in the same year, or as a percentage of the base case scenario in 2020.
Subgroup: results can be shown for the total population, or for a subgroup described by nativity (U.S.-born, non-U.S.-born), and broad age groups (0-24 years, 25-64 years, 65+ years).
Outcome: results can be shown for five different outcomes:
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Incident TB infections representing the annual number of incident M. tuberculosis (Mycobacterium tuberculosis) infections per 100,000 due to transmission within the United States (includes reinfection of individuals with prior LTBI, excludes migrants entering the United States with established LTBI);
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LTBI Prevalence representing the percentage of individuals with latent TB infection in a given year;
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TB Incidence representing the annual number of notified TB disease cases per 100,000, including those after death;
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TB-Related Deaths representing annual TB-attributable mortality per 100,000.
Scenarios: results can be shown for up to five scenarios selected by the user, describing hypothetical changes to current TB prevention and control activities ("Modelled Scenarios").
Download: clicking on a button initiates download of the visualization itself (.png, .pdf, .pptx) or the estimates underlying the visualization (.csv, .xlsx).
This page matches the format of the first two pages with the following exceptions:
Comparison: results are only shown as absolute values for each outcome in each year.
Subgroup: results can be shown for the total population, or for U.S.-born and non-U.S.-born alone.
Outcomes: results can be shown for three major outcomes (LTBI prevalence, TB incidence, and TB-related deaths), either as a prevalence or incidence rate with each age group (first three selections), or in absolute numbers (last three selections).
User options are shown in a column on the left. The user specifies:
Comparison: results can be shown as absolute values for each outcome in each year, as a percentage of the base case scenario in the same year, or as a percentage of the base case scenario in 2020.
Subgroup: results can be shown for the total population, or for a subgroup described by nativity (U.S.-born, non-U.S.-born), and broad age groups (0-24 years, 25-64 years, 65+ years).
Outcome: results can be shown for five different outcomes:
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LTBI Tests representing the annual sum of TST and IGRA tests.;
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LTBI Treatment Initiations representing the annual number of those testing positive who initiate LTBI treatment with any regimen.;
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LTBI Treatment Completions representing the number of those initiating LTBI treatment who complete their treatment.
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Active TB Treatment Initiations representing the number of those diagnosed with TB disease that begin treatment.
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• Active TB Treatment Completions representing the number of those initiating TB treatment who complete their treatment in the first round.
Scenarios: results can be shown for up to five scenarios selected by the user, describing hypothetical changes to current TB prevention and control activities ("Modelled Scenarios").
Download: clicking on a button initiates download of the visualization itself (.png, .pdf, .pptx) or the estimates underlying the visualization (.csv, .xlsx).
The Comparison to Recent Data Page
In the Comparison to Recent Data page (Figure 7), users can compare the model's output to reported data on the demography and TB epidemiology for their selected geography.
Economic Analyses are presented as three interactive pages with tabular inputs and results: Input Costs, Costs and Outcomes, and Cost Effectiveness Comparison.
The Input Costs page presents the user with the opportunity to input unit costs of services associated with treatment of LTBI and TB. The user can also select the analytical horizon for the costs and outcomes (the period over which total costs and outcomes are calculated.
The Costs and Outcomes page provides data tables reporting the outcomes and costs associated with each of the modelled scenarios. These are provided in annual and cumulative perspectives.
The Cost Effectiveness Comparison page provides a cost effectiveness table for the modelled scenarios.
A detailed description of each of these pages is provided below.
The user is presented with a table of estimated average unit costs. Each of these values is editable prior to submitting a costing calculation. Additional information about the calculation of the national average estimates can be found in our costing methodology document.
The user specifies:
LTBI Testing Costs:
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Cost of identifying an individual for LTBI testing representing the average cost to a health program to identify an individual for LTBI testing.;
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Cost of a Mantoux tuberculin skin test (TST) representing the average health services cost for a single TST.;
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Cost of an IGRA representing the average health services cost for a single IGRA.;
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Cost of ruling out TB disease before LTBI treatment representing the health services costs associated with excluding TB disease. Currently calculated as two chest x-rays and a sputum culture.;
LTBI Treatment Costs: representing the average per-patient cost of medication, clinic visits, and managing adverse reactions for each of the listed regimens.
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Cost of treatment with 3HP
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Cost of treatment with 4R
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Cost of treatment with 3HR
TB Disease Identification and Treatment Costs:
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Cost of identifying an individual for TB testing representing the average cost to a health program to identify an individual for TB testing.;
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Cost of TB disease diagnosis representing the health services costs associated with definitively diagnosing TB disease. Currently calculated as one chest x-ray and three sputum cultures.;
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Cost of TB disease treatment representing the average cost of TB treatment for non-MDR, MDR, and XDR TB.
End year for economic analysis:
The costs and outcomes in the following pages will be calculated from 2020 until the end year selected by the user.
The user is presented with two tabs:
Summary Tables: These tables present the estimated cumulative costs and outcomes associated with each of the modelled scenarios from 2020 to the end year for economic analysis specified on the Input Costs page.
Annual Table: This table presents the estimated costs and outcomes associated with each of the of modelled scenarios summed over each year from 2020 to the end year for economic analysis specified on the Input Costs page.
User options are shown in a column on the left. The user specifies:
Scenarios: results can be shown for up to five scenarios selected by the user, describing hypothetical changes to current TB prevention and control activities (“Modelled Scenarios”).
Download: clicking on a button initiates download of the three data tables (.csv, .xlsx).
User options are shown in a column on the left. The user specifies:
Scenarios: results can be shown for up to five scenarios selected by the user, describing hypothetical changes to current TB prevention and control activities (“Modelled Scenarios”).
ICER/ACER:
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Compare incremental cost effectiveness of scenarios the costs and benefits of each scenario are compared to the next most beneficial scenario, after dominated strategies have been removed (incremental cost effectiveness ratio, ICER). Dominated strategies represent those that have higher costs and lower health benefits than another strategy, or linear combination of other strategies.;
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Compare all scenarios to the base case the costs and benefits of each scenario are compared to the base case scenario (average cost effectiveness ratio, ACER).
Effectiveness Measure:
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TB cases averted representing the cumulative notified TB disease cases averted (including those identified after death), as compared to the base-case scenario.;
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TB deaths averted representing cumulative TB-attributable mortality averted, as compared to the base-case scenario.;
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QALYs saved representing cumulative QALYs gained, as compared to the base-case scenario.;
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Life years saved representing cumulative life years gained, as compared to the base-case scenario.
Costing Perspective: the selection determines which costing perspective is used in the calculations of the cost effectiveness ratio.
Discounting: selecting Include applies a 3% annual discount to both health and economic outcomes prior to the calculation of the cost effectiveness ratio. Otherwise costs and health outcomes are undiscounted in cost-effectiveness calculations.
Download: clicking on a button initiates download of a data table (.csv, .xlsx) containing the cost-effectiveness results.
In this Further Description page of the Tabby2 web application, documentation detailing the Organization of the tool, Definitions and Abbreviations, Frequently Asked Questions, and a notice about the 508 Accessibility of This Product are provided.
The Feedback page in the Tabby2 web application prompts users of the application with feedback to either email ppml@hsph.harvard.edu with their questions, comments, or feedback, or to submit it directly through the web application.
How do I export data from Tabby2?
Tabby2 users are able to download the data visualizations that they have created using the "Estimates", "Time Trends", or "Age Groups" tabs and the underlying estimates that were used to generate their visualizations.
To download a data visualization:
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Navigate to the last heading on the "Estimates," "Time Trends," or "Age Groups" tab, which reads "Download" (this can be found on the bottom left-hand corner of a typical web browser)
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Select PNG or PDF or PPTX depending on desired format
To download underlying data estimates:
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Navigate to the last heading on the "Estimates," "Time Trends," or "Age Groups" tab, which reads "Download" (this can be found on the bottom left-hand corner of a typical web browser)
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Select CSV or XLSX depending on desired format
Downloads should begin immediately after selection. If not, contact ppml@hsph.harvard.edu for assistance.
General information and resources on tuberculosis can be found on the Centers for Disease Control and Prevention's Tuberculosis webpage: https://www.cdc.gov/tb/default.htm
Section 508 requires Federal agencies and grantees receiving Federal funds to ensure that individuals with disabilities who are members of the public or Federal employees have access to and use of electronic and information technology (EIT) that is comparable to that provided to individuals without disabilities, unless an undue burden would be imposed on the agency.
If you need assistance with this web application, please contact ppml@hsph.harvard.edu.