Clinical Overview of Tuberculosis

Key points

Tuberculosis (TB) is caused by a bacterium called Mycobacterium tuberculosis (M. tuberculosis). TB disease is one of the leading causes of death due to infectious disease in the world. TB disease is preventable and curable.

Two health care providers review a patient's chest x-ray.


Tuberculosis (TB) is an airborne disease caused by the bacterium Mycobacterium tuberculosis (M. tuberculosis). M. tuberculosis and seven very closely related mycobacterial species (M. bovis, M. africanum, M. microti, M. caprae, M. pinnipedii, M. canetti, and M. mungi) comprise what is known as the M. tuberculosis complex. Most—but not all—of these species have been found to cause disease in humans.

In the United States, the majority of TB cases are caused by M. tuberculosis. M. tuberculosis organisms are also called tubercle bacilli or TB bacteria. TB bacteria usually attack the lungs but can attack any part of the body such as the kidney, spine, and brain. TB can also affect multiple parts of the body at the same time. For example, TB can affect both the lungs and lymph nodes.

Not everyone infected with TB bacteria becomes sick. As a result, two TB-related conditions exist: latent TB infection (or inactive TB) and TB disease. People with latent TB infection can be treated to prevent the development of TB disease.

Health care providers should immediately contact their state TB program office if they have a patient with presumed or confirmed TB disease. If not treated properly, TB disease can be fatal.

For Everyone: About Tuberculosis


Persons with latent TB infection have TB bacteria in their bodies, but do not have symptoms of TB disease and cannot spread the infection to other people.

The process of latent TB infection begins when extracellular bacilli that are in the alveoli are ingested by macrophages and presented to other white blood cells. This triggers the immune response in which white blood cells kill or encapsulate most of the bacilli, leading to the formation of a granuloma. Once this happens, latent TB infection has been established. People with latent TB infection can be treated to prevent the development of TB disease.

Without treatment, approximately 5% of persons who have been infected with TB bacteria will develop TB disease in the first two years after infection, and another 5% will develop TB disease sometime later in life.

In some people, the TB bacteria overcome the immune system and multiply, resulting in progression from latent TB infection to TB disease. Persons who have TB disease are usually infectious and may spread the bacteria to other people.

The progression from latent TB infection to TB disease may occur at any time, but it is most common within the first two years of infection or in the context of certain medications or health conditions (such as diabetes, cancer, or HIV).

TB disease can occur in different places in the body and in more than one organ or organ system at the same time.

  • Pulmonary TB disease occurs in the lungs. Most cases of TB disease are pulmonary.
  • Extrapulmonary TB disease occurs in places other than the lungs, such as the larynx, lymph nodes, pleura, brain (TB meningitis), kidneys, or bones.
  • Disseminated TB disease (or miliary TB disease) occurs when TB bacteria enter the bloodstream and are carried to all parts of the body where they grow and cause disease in multiple sites.

Drug-resistant TB disease

Drug-resistant TB disease is caused by TB bacteria that are resistant to the drugs normally used to treat the disease.

Drug-resistant TB is transmitted in the same way as drug-susceptible TB, and it is no more infectious than drug-susceptible TB. However, delay in the recognition of drug resistance or prolonged periods of infectiousness may facilitate increased transmission and further development of drug resistance.

Difference between latent TB infection and TB disease
Person with latent TB infection Person with TB disease
Has a small amount of TB bacteria in the body that are alive but inactive Has a large amount of active TB bacteria in the body
Cannot spread TB bacteria to others May spread TB bacteria to others
Does not feel sick, but may become sick if the bacteria in the body become active May feel sick, and may have symptoms such as a cough, fever, and/or weight loss
Usually has a positive TB blood test or TB skin test result indicating TB infection Usually has a positive TB blood test or TB skin test result indicating TB infection
Chest radiograph is typically normal Chest radiograph may be abnormal
Sputum smears and cultures are negative Sputum smears and cultures may be positive
Should consider treatment for latent TB infection to prevent TB disease Needs treatment for TB disease
Does not require respiratory isolation May require respiratory isolation
Is not a TB case Is a TB case

Risk factors

People at risk for TB fall into two broad categories:

  • People who are at high risk of exposure to or infection with TB bacteria
  • People who are at high risk of developing TB disease once infected with TB bacteria

  • Contacts of people known or presumed to have infectious TB disease
  • People who were born in or who frequently travel to countries where TB disease is common
  • People who currently live or used to live in large group settings where TB is more common, such as homeless shelters, correctional facilities, or nursing homes
  • Employees of high-risk congregate settings
  • Health care workers who serve patients with TB disease
  • Populations defined locally as having an increased incidence of latent TB infection or TB disease, possibly including medically underserved populations, low-income populations, or persons with alcohol use or substance use disorders
  • Infants, children, and adolescents exposed to adults who are at increased risk for latent TB infection or TB disease

  • People with HIV
  • Children younger than 5 years of age
  • People recently infected with TB bacteria (within the last 2 years)
  • People with a history of untreated or inadequately treated TB disease
  • People who are receiving immunosuppressive therapy such as tumor necrosis factor-alpha (TNF) antagonists, systemic corticosteroids equivalent to/greater than 15 mg of prednisone per day, or immunosuppressive drug therapy following organ transplantation
  • People with silicosis; chronic renal failure; leukemia; or cancer of the head, neck, or lung
  • People with diabetes mellitus
  • People who have had a gastrectomy or jejunoileal bypass
  • People with low body weight (<90% of ideal body weight)
  • People who use substances (such as injection drug use)
  • Populations defined locally as having an increased incidence of TB disease, including medically underserved and low-income populations

How it spreads

TB bacteria are carried in airborne particles of 1–5 microns in diameter called droplet nuclei. Infectious droplet nuclei are generated when a person with pulmonary or laryngeal TB disease coughs, speaks, or sings.

Depending on the environment, these tiny particles can remain suspended in the air for several hours. TB bacteria are transmitted through the air, not by surface contact. TB bacteria are more likely to spread in indoor areas or other places with poor air circulation (such as a closed vehicle) than outdoor areas.

Transmission occurs when a person inhales droplet nuclei containing TB bacteria, and the droplet nuclei traverse the mouth or nasal passages, upper respiratory tract, and bronchi to reach the alveoli of the lungs.

Disease rates

CDC estimates that up to 13 million people in the United States live with latent TB infection. More than 80% of TB disease cases in the United States result from longstanding, untreated latent TB infection.

In 2022, the United States reported 8,331 cases of TB disease, representing a 5.9% increase in case count compared with 2021. The incidence rate was 2.5 cases per 100,000 persons, a 5.5% increase in incidence rate compared with 2021.

Signs and symptoms

Persons with latent TB infection do not have symptoms of TB disease, and they cannot spread TB bacteria to others.

Not everyone with TB disease has signs and symptoms. However, most individuals with TB disease have one or more symptoms that lead them to seek medical care. Symptoms of TB disease may vary depending on the part of the body affected.

When the onset of TB disease is gradual, a person who has TB disease might not notice the symptoms because they seem mild and do not interfere with daily activities.

Symptoms of pulmonary TB disease

  • Cough (especially lasting for 3 weeks or longer)
  • Coughing up sputum or blood (hemoptysis)
  • Chest pain
  • Loss of appetite
  • Unexplained weight loss
  • Night Sweats
  • Fever
  • Fatigue

Symptoms of extrapulmonary TB disease

Extrapulmonary TB disease, which affects organs in addition to or instead of the lungs, may cause symptoms related to the part of the body that is affected. For example, TB disease of the spine may cause back pain, TB disease of the kidney may cause blood in the urine, and TB meningitis may cause headache or confusion.


Preventing TB in health care settings

Health care settings should have a TB infection control plan designed to ensure early and prompt:

Testing and diagnosis

TB testing activities should be done only when there is a plan for follow-up care to evaluate and treat all individuals diagnosed with latent TB infection or TB disease. Contact your state or local TB program for more information.

The CDC and the U.S. Preventive Services Task Force (USPSTF) recommend testing people who are at increased risk for TB infection. Testing for TB infection should be a routine and integral part of health care for patients with increased risk for TB. Frequency of testing depends on a person's risk factors. This could range from one-time only testing among persons at low risk for future TB exposure to annual testing among those at continued risk of exposure.

There are two first-line diagnostic tests that are used to determine if a person has been infected with TB bacteria: the TB blood test (Interferon Gamma Release Assays [IGRAs]) and the TB skin test (Mantoux tuberculin skin test).

Test results should be interpreted in the context of the likelihood of infection (pretest probability) and medical conditions such as an illness that is suggestive of TB disease.

A positive reaction to a TB blood test (IGRA) or TB skin test usually means TB infection. More tests are needed to rule out TB disease.

Diagnosing latent TB infection

A diagnosis of latent TB infection is made if a person has a positive TB blood test or TB skin test result, and a medical evaluation does not indicate TB disease.

Diagnosing TB disease

People with a positive TB blood test or TB skin test result for TB infection should be evaluated for TB disease. An evaluation for TB disease includes

  • A review of systems (medical history) to determine if the patient:
    • Has been exposed to TB bacteria,
    • Has been treated for latent TB infection or TB disease in the past, or
    • Has medical conditions that should be considered during the evaluation and subsequent treatment.
  • Chest radiography; and,
  • Laboratory tests (sputum smear microscopy, nucleic acid amplification testing, culture, and drug susceptibility testing)

Culture is the gold standard microbiologic test for the diagnosis of TB disease.

Treatment and recovery

There are several regimens for the treatment of latent TB infection. Regimens use one or more of the following drugs:

  • Isoniazid (H)
  • Rifapentine (P)
  • Rifampin (R)

These drugs are selected when the infection is assumed to be drug susceptible. If drug resistance is being considered because of the exposure history, consult with a TB expert.

CDC and the National Tuberculosis Coalition of America preferentially recommend short-course, rifamycin-based, 3- or 4-month latent TB infection treatment regimens over 6- or 9-month isoniazid monotherapy. Short-course regimens are effective, safe, and have higher completion rates than longer regimens.

Short course regimens include:

  • Three months of once-weekly isoniazid plus rifapentine (3HP)
  • Four months of daily rifampin (4R)
  • Three months of daily isoniazid plus rifampin (3HR)

Multiple options for therapy are available. Treatment for drug-susceptible TB disease can take 4, 6, or 9 months depending on the regimen. Regimens include:

The goal of treatment for TB disease should be to provide the safest and most effective therapy for the shortest period. Health care providers, with input from local or state TB programs, should choose the TB treatment regimen based on drug-susceptibility results, coexisting medical conditions, and potential for drug-drug interactions.

Given adequate treatment, almost all patients will recover and be cured.

To help patients complete treatment for TB disease, use in-person directly observed therapy (DOT) or video directly observed therapy (vDOT). Contact your local health department for assistance with arranging DOT or vDOT. Many health departments have programs to help monitor treatment for TB disease.

Treating drug-resistant TB disease is complicated. Inappropriate management can have life-threatening results. Drug-resistant TB disease should be managed by or in close consultation with an expert in the disease.