At a glance
This glossary includes definitions for commonly used tuberculosis (TB) terms and concepts.
A - F
A
Acid-fast bacilli (AFB) – a type of bacteria that keep the color of a stain even when washed in an acid solution. TB germs are acid-fast bacilli. Laboratory staff may look for acid-fast bacilli in a patient's sputum sample. If the acid-fast bacilli are present, it means that TB germs are in the sample.
Active TB disease – happens when the immune system cannot keep TB germs from multiplying and growing in the body. People with active TB disease feel sick and can spread TB germs to others. Active TB disease can almost always be treated and cured with medicine. Without treatment, active TB disease can be fatal.
B
Bacille Calmette-Guérin (BCG) – a vaccine for active TB disease. The vaccine is not generally used in the United States. It is given to infants and small children in countries where TB is common. It protects children from getting severe forms of active TB disease, such as TB meningitis.
Tell your health care provider if you have received the TB vaccine, especially if you are getting tested for TB infection because it can cause a false positive TB skin test reaction. TB blood tests, also known as interferon-gamma release assay (IGRA), are the preferred tests for people who have received the BCG TB vaccine.
Boosted reaction – a positive reaction to a TB skin test, also known as tuberculin skin test (TST), due to a boosted immune response from a TB skin test given in the past year. Health care providers use two-step testing to help tell the difference between boosted reactions and recent infection. This two-step approach can lower the chances that a boosted reaction from an old infection with TB germs will be misinterpreted as a recent infection. If the test result for the first TB skin test is negative, a second TB skin test is given one to three weeks later.
Booster phenomenon – an event in which some people, especially older adults, who receive a TB skin test many years after being infected with TB germs may have a negative reaction to an initial TB skin test, followed by a positive reaction to a TB skin test given up to a year later. The first TB skin test "triggered the memory" of the immune system, boosting its ability to react to the second TB skin test. Two-step testing is used to tell the difference between boosted reactions and recent infection.
C
Chest x-ray – a picture of the inside of your chest. During a chest x-ray, also known as a chest radiograph, x-rays pass through your chest and create an image on film. A health care provider may look at a chest x-ray to see if there are signs of active TB disease in your lungs.
Civil surgeon – physicians who conduct medical examinations of persons living in the United States and applying for lawful permanent residence.
Cluster investigation – a process to identify connections between people with TB disease who have matching TB genotypes. See also "genotype cluster."
Congregate setting – a place where people live and work close to each other, such as correctional and detention facilities, nursing homes, schools, and homeless service sites.
Contact – a person who spent time around someone with active TB disease. Contacts of someone with active TB disease may need to be tested for TB.
If you have active TB disease, your contacts may include:
- People in the same household,
- Family members,
- Friends,
- Coworkers,
- Classmates,
- Neighbors, and
- Anyone else who spent time with you while you were able to spread TB germs.
Contact investigation – sometimes referred to as "contact tracing", the process of identifying people who have recently been in contact with someone diagnosed with an infectious disease. Contact tracing is the process of quickly identifying, assessing, and managing people who have been exposed to a disease to prevent additional transmission.
Continuation phase – a phase in the treatment plan for active TB disease. It occurs after the intensive phase and aims to kill the remaining TB germs. This helps to lower the chances of the treatment plan not working, or active TB disease coming back after finishing the treatment plan. Depending on the treatment plan, your TB medicines may change.
Counting of a TB case – a process to confirm a case of TB disease and ensure the case is not counted twice. Local health authorities count TB cases in a specific area and report the cases to CDC.
Culture – a laboratory test to see whether there are TB germs in your sputum (or phlegm) or other body fluids. Results from this test can take two to four weeks to process.
D
Diabetes – a chronic (long-lasting) health condition that affects how your body turns food into energy. A person with diabetes is at higher risk for developing active TB disease once infected with TB germs.
Directly observed therapy (DOT) – a way to help people take their medicine for TB infection. Through DOT, you will meet with a health care worker every day or several times a week. These meetings may be in-person or virtual (through a smartphone, tablet, or computer). The health care worker will watch you take their TB medicines and make sure that the TB medicines are working as they should.
Disseminated TB – a type of active TB disease that occurs when TB germs enter the bloodstream or lymph system and spread to other parts of the body. TB germs grow and cause disease in multiple sites of the body, e.g., miliary TB.
Drug-resistant TB disease – a form of active TB disease in which some TB medicines can no longer kill the TB germs. Drug-resistant TB disease occurs when TB germs are resistant to at least one of the most effective TB medicines.
E
Epidemiologic (epi) link – a connection between two people with TB disease that might explain where, when, and how one person spreads TB germs to the other person.
Ethambutol – a first-line medicine to treat active TB disease.
Exposure to TB – when a person spends time with someone who has active TB disease
Extensively drug-resistant TB (XDR TB) – a rare type of active TB disease that is resistant to nearly all medicines used to treat active TB disease.
Extrapulmonary TB – a form of active TB disease that occurs in any part of the body other than the lungs (such as the brain, kidneys, or the spine).
F
False-negative reaction – a reaction to a TB skin test or TB blood test that says a person does not have TB germs in their body, but they do have TB germs in their body.
False-positive reaction – a reaction to a TB skin test or TB blood test that says a person has TB germs in their body, but they do not have TB germs in their body.
First-line treatment drugs – a group of medicines to treat active TB disease that make up the most powerful, least expensive, and most tolerable treatment plan. The medicines include isoniazid, rifampin, ethambutol, and pyrazinamide.
Fluoroquinolone – a class of synthetic broad-spectrum antibacterial medicines; examples of fluoroquinolones to treat TB infection are levofloxacin and moxifloxacin.
G - K
G
Genotype – a distinct genetic pattern of an organism.
Genotype cluster – a group of 2 or more TB cases withTB germs that share the same genotype in a specific area during a specific period. In the United States, cases with the same wgMLSType belong to the same genotype cluster. CDC uses a single county or county equivalent and a 3-year period to define a cluster.
Genotype cluster alert level – CDC classifies TB genotype clusters into three levels based on their log-likelihood ratio (LLR) values: no alert (LLR 0–<4), medium alert (LLR 4–<10) or high alert (LLR ≥10). See also "log-likelihood ratio" and "genotype cluster."
Genotype surveillance coverage – the percentage of culture-positive TB cases with a genotype result.
Genotyping – a laboratory-based approach to identify the genetic material, or "make-up", (e.g., DNA) of the germs that caused active TB disease in a person. TB programs may use TB genotyping results to help find people with active TB disease who may be connected and spread active TB disease to each other. TB genotyping is a helpful tool for contact investigations.
GENType – a U.S. molecular surveillance designation that used spoligotyping and 24-locus MIRU-VNTR results. GENType designated each genotype with a G followed by 5 digits, which was sequentially assigned to every genotype identified in the United States (e.g., G00017) during 2009–2022. See also "spoligotyping" and "mycobacterial interspersed repetitive unit - variable number tandem repeat."
Geospatial concentration – a measure of the number of cases with a given genotype in a specific area during a specific time period which may suggest recent transmission.
H
HIV infection – a person with human immunodeficiency virus (HIV) infection is at higher risk of becoming sick with active TB disease once exposed to TB germs compare with people who do not have HIV. HIV weakens the immune system, which makes it harder for the body to fight TB germs.
I
Immune system – cells and tissues in the body that protect the body from unfamiliar substances, like TB germs. Active TB disease happens when the immune system cannot keep TB germs from multiplying and growing in the body.
Inactive TB – a condition in which TB germs live in your body without making you sick. Inactive TB is also known as latent TB infection. People with inactive TB do not feel sick, do not have symptoms, and cannot spread TB to others. Without treatment, inactive TB can develop into active TB disease at any time and make you sick.
Index case – the first person diagnosed with active TB disease, also called the initial TB case, that leads to a contact investigation.
Infection control procedures – a set of measures to prevent the spread of active TB disease. These measures include administrative procedures, environmental controls, and using respiratory protective equipment.
Infectious – a person's ability to spread TB germs into the air when he or she coughs, speaks, or sings.
Intensive phase – a phase in the treatment plan for active TB disease. It occurs before the continuation phase. During the intensive phase, you take strong medicines to kill as many TB germs as quickly as possible. Depending on the treatment plan, you may take a combination of TB medicines for a specific amount of time.
Interferon-gamma release assay (IGRA) – see "TB blood test"
Isolate – a sample of TB germs from sputum (or phlegm) or other body fluids. See also "culture."
Isoniazid – a first-line medicine used to treat inactive TB and active TB disease.
L - P
L
Latent TB infection – see "inactive TB"
Log-likelihood ratio (LLR) – a measure of the geographic concentration of a specific genotype in a county compared with its national distribution during a 3-year period. A higher LLR means greater clustering of a given genotype in the county, suggesting possible recent transmission (spread) of TB germs.
M
Medical evaluation – a process in which your health care provider collects information to diagnose inactive TB or active TB disease. A medical evaluation includes:
- Medical history
- Physical examination
- Test for TB infection (TB blood test or TB skin test)
- Chest x-ray
- Laboratory tests to see if TB germs are present (sputum smear and culture)
- Laboratory tests for drug resistance
Medical history – a health care provider will ask you questions about your health to diagnose you with inactive TB or active TB disease as part of a medical evaluation. The health care provider may ask you if you have:
- Symptoms of active TB disease,
- Spent time with someone who has active TB disease,
- Ever had a positive TB blood test or TB skin test,
- Ever been diagnosed with inactive TB or active TB disease in the past, or
- Factors that may increase your risk for becoming infected with TB germs.
Miliary TB – a type of active TB disease that occurs when TB germs enter your bloodstream and spread to other parts of the body where they grow and cause disease in multiple sites. The chest x-ray of a person with miliary TB often looks like millet seeds scattered throughout the lung.
Moxifloxacin – a type of fluoroquinolone used to treat active TB disease.
Multidrug-resistant TB (MDR TB) – a type of active TB disease caused by TB germs that are resistant to two or more of the main TB medicines: isoniazid and rifampin.
Mycobacterial interspersed repetitive unit–variable number tandem repeat (MIRU-VTNR) – a polymerase chain reaction (PCR)-based assay that was used for genotyping during 2004–2022. MIRU-VTNR distinguished Mycobacterium tuberculosis strains by the difference in the number of copies of tandem repeats at specific regions, or loci, of the Mycobacterium tuberculosis genome.
Mycobacterium bovis – a member of the Mycobacterium tuberculosis complex (MTBC) commonly associated with cattle and deer. It can infect other mammals, including humans, causing disease similar to Mycobacterium tuberculosis. Today, M. bovis rarely affects people in the United States. Human cases are often linked to consuming contaminated foods, such as unpasteurized milk or dairy products. Before pasteurization became common practice, humans usually were infected with these TB germs through contaminated milk.
Mycobacterium tuberculosis – the germ that causes inactive TB and active TB disease.
Mycobacterium tuberculosis complex (MTBC) – a group of closely related mycobacterial species that can cause inactive TB and active TB disease. Most TB cases among humans result from Mycobacterium tuberculosis. MTBC includes:
- Mycobacterium africanum
- Mycobacterium bovis
- Mycobacterium bovis bacillus Calmette–Guérin
- Mycobacterium canetti
- Mycobacterium caprae
- Mycobacterium microti
- Mycobacterium mungi
- Mycobacterium orygis
- Mycobacterium pinnipedii
- Mycobacterium suricattae
- Mycobacterium tuberculosis
N
Negative – "negative" usually refers to test results showing that TB germs are not present in your body. For example, if a TB blood test result or TB skin test result is negative, it means that you do not have TB germs in your body and inactive TB or active TB disease is unlikely. A negative culture means that the culture did not find any TB germs. Your health care provider may do more tests, especially if:
- You have symptoms of active TB disease, like coughing, chest pain, fever, weight loss, or tiredness.
- You have HIV.
- You were recently exposed to TB germs.
Nontuberculous mycobacteria – mycobacteria other than Mycobacterium tuberculosis complex that can cause human infection or disease. Common nontuberculous mycobacteria (NTM) include:
- Mycobacterium avium, Mycobacterium intracellulare, and other members of the Mycobacterium avium complex (also known as "MAC" or "MAI")
- Mycobacterium chelonae
- Mycobacterium fortuitum
- Mycobacterium kansasii
- Mycobacterium marinum
- Mycobacterium scrofulaceum
- Mycobacterium simiae
Other terms to represent NTM include "MOTT" (mycobacteria other than TB) and "atypical" mycobacteria.
Nucleic acid amplification (NAA) – a technique that copies pieces of genetic material. Laboratory staff often use it to detect TB germs in clinical specimens.
P
Panel physician – panel physicians work overseas and conduct examinations (including TB screening) on people who apply for immigrant or refugee status before coming to the United States.
PCRType – a U.S. molecular surveillance designation that used spoligotyping and 12-locus MIRU-VNTR results during 2004–2022. PCRType is written as PCR followed by the 5 digits sequentially assigned to every genotype identified in the United States (e.g., PCR01974). See also "spoligotyping" and "mycobacterial interspersed repetitive unit–variable number tandem repeat."
Polymerase chain reaction (PCR) – a laboratory method that quickly multiplies small amounts of DNA to enable certain types of laboratory testing.
Positive – "positive" usually refers to test results showing that TB germs are present in your body. For example, if a TB blood test result or TB skin test result is positive, it means that you have TB germs in your body. Your health care provider will do other tests to determine if you have inactive TB or active TB disease. These tests may include a chest x-ray, and a test of the sputum (phlegm) you cough up. A positive culture means that the culture did find TB germs.
Presumed TB case – an illness that may be active TB disease and may require a medical evaluation for TB disease. Similar terms include "possible TB case" or "suspected TB case."
Pulmonary TB – a form of active TB disease that occurs in the lungs, typically causing a cough and an abnormal chest x-ray. Pulmonary TB can usually spread to others if untreated. Most active TB disease cases are pulmonary TB.
Pyrazinamide – a first-line medicine to treat inactive TB and active TB disease.
Q - U
R
Reinfection – a second infection, usually caused by a different strain (genotype) of TB germsthan the first infection. See also "relapse."
Relapse – a clinical worsening of TB disease after the person received treatment and improved. The same strain (genotype) of TB germscauses a relapse. Genotyping the first and later Mycobacterium tuberculosis isolates (TB germs) can help distinguish relapse from reinfection. See also "reinfection."
Reporting area – an area responsible for counting and reporting verified TB disease cases to CDC. In total, 60 areas report cases to CDC, including:
- 50 U.S. states, New York City, and the District of Columbia (D.C.)
- Five U.S. territories (American Samoa, Commonwealth of the Northern Mariana Islands, Guam, Puerto Rico, and the U.S. Virgin Islands)
- Three independent countries that are in compacts of free association with the United States (Federated States of Micronesia, Republic of the Marshall Islands, and Republic of Palau)
Resistant bacteria – germs that medicine cannot kill.
Rifampin (RIF) – a first-line medicine used to treat inactive TB and active TB disease.
Rifapentine (RPT) – a medicine to treat both inactive TB and active TB disease.
S
Smear – a laboratory test to see if you have TB germs in your sputum (phlegm). To do this test, laboratory staff smear the sputum on a glass slide and stain the slide with a special stain. The laboratory staff look for any TB germs on the slide. This test usually takes one day to get the results.
Spacer oligonucleotide typing (spoligotyping) – a method that identified spacer sequences located in the direct repeat region of the chromosomes of Mycobacterium tuberculosis complex (MTBC). The spoligotype used an octal code to report as a 15-digit number. Spoligotyping was performed on every isolate submitted for genotyping from 2004–2022.
Sputum – a substance (also called phlegm) coughed up from deep inside the lungs. Your health care provider may examine sputum for TB germs using a smear test. They can also use a part of the sputum for a culture test to see if TB germs grow.
T
TB blood test – a TB blood test (also called an interferon-gamma release assay (IGRA) uses a blood sample to find out if have TB germs in your body. The test measures how your immune system reacts when a small amount of your blood is mixed with TB proteins. The TB blood test requires only one visit with your healthcare provider. Your health care provider will use one of the two TB blood tests approved for use in the United States: QuantiFERON®-TB Gold Plus (QFT-Plus) or T-SPOT®.TB test (T-Spot).
TB case – a person with presumed or confirmed active TB disease who meets laboratory or clinical criteria.
TB meningitis – an illness that occurs when TB germs infect the tissue surrounding the brain or spinal cord. Symptoms may include headache, decreased level of consciousness, and neck stiffness.
TB outbreak – occurs when there are more people with active TB disease (TB cases) than expected in a certain geographic area (i.e., a city) or a group of people (i.e., people who work at a particular nursing home) during a particular time, and TB germs are spreading.
TB skin test – a TB skin test (known as the tuberculin skin test (TST)) helps to find out if you have TB germs in your body. The TB skin test requires two visits with your healthcare provider. During the first visit, a health care provider uses a small needle to put some testing material under the skin. You will need to return to your health care provider in two to three days to have the test read.
Transmission (spread) – a process of one person with active TB disease giving TB germs to another person. The chances of a person with active TB disease spreading TB germs to others depends on factors that may include:
- How likely the person with active TB disease is to spread TB germs (i.e., infectiousness)
- Where the people are (e.g., in close proximity to each other or in an area with poor air flow)
- How much time is spent around a person with active TB disease
- How likely the person exposed to TB germs is to get sick (i.e., if they have a weakened immune system)
Treatment plan – also referred to as "treatment regimen", is a schedule to take TB medicines to kill all the TB germs. Your treatment plan for inactive TB or active TB disease will include:
- The types of TB medicines to take,
- How much TB medicine to take,
- How often to take the TB medicines,
- How long to take the medicines,
- How to monitor yourself for any side effects of your TB medicine, and
- The health care provider(s) who will support you through the treatment process.
Tuberculin – a testing fluid (also known as purified protein derivative (PPD)) for TB germs used in the TB skin test. During the first visit, a health care provider uses a small needle to put tuberculin under the skin on the lower part of your inner arm. After two or three days, you must return to the clinic to have the skin test read. A trained health care provider will measure the size of the bump or reaction.
Two-step testing – a testing process to tell the difference between a boosted reaction to a TB skin test compared with a recent infection with TB germs. A two-step approach can lower the chances that a boosted reaction from an old infection with TB germs will be misinterpreted as a recent infection. If the test result for the first TB skin test is negative, a second TB skin test is given one to three weeks later.
V - Z
V
Verification of a TB case – a process to confirm and count a case of TB disease.
Video DOT (vDOT) – a type of directly observed therapy (DOT) to help people complete treatment for TB. During vDOT, you will use a video-enabled device, such as a smartphone, tablet, or computer, to meet with a health care provider. The health care provider will watch you take your TB medicine virtually.
W
wgMLSType – a U.S. molecular surveillance designation for each wgMLST result. CDC assigns wgMLSType to isolates with wgMLST that cluster nationally, defined as matching at ≥99.7% of their loci. These isolates receive a designation of Mycobacterium tuberculosis complex (MTBC) followed by 6-digits (e.g., MTBC000123). Isolates that do not match are designated as "MTBCunique. Since 2018, wgMLSType has been available, and it is the sole genotype designation used since July 2022.
Whole-genome multilocus sequence typing (wgMLST) – a genotyping scheme that uses whole-genome sequencing (WGS) information to compare sequences at 2,690 loci (about 70% of the Mycobacterium tuberculosis complex [MTBC] genome). A locus refers to a specific location in the genome (i.e., one gene).
Whole-genome sequencing (WGS) – a method that generates usable DNA sequence information for about 90% of the Mycobacterium tuberculosis genome.