What Is Tuberculosis?

Tuberculosis (TB) is an infectious disease. It is caused by a type of bacteria called Mycobacterium tuberculosis (Mtb). TB is the leading cause of death from an infection globally. TB often affects the lungs. However, it may involve any organ and may infect anyone at any age. When it affects the lungs, it is called pulmonary TB.  

This disease is spread when a person with TB in their lungs coughs and inadvertently sprays Mtb bacteria in the air. While Mtb can remain in the air in very small droplets or an aerosol for hours, it’s actually somewhat difficult to spread. Generally, you need to be in contact for several hours at a time with someone who has active TB in their lungs before you can acquire TB. 

Not everyone who inhales the Mtb bacteria develops active TB disease. Most individuals have no symptoms for weeks to years after becoming infected. This is called latent TB. In most tuberculosis infections, the body's natural defenses are able to control the infection and a person does not become ill with TB. Only about 5-10 % of those infected will develop active disease in their lifetimes. Instead, the bacteria persist as a latent TB infection, which cannot be spread to other people. When the body's immune system detects the bacteria, it surrounds them with immune cells. This creates collections of cells known as granulomas that effectively cut off the bacteria from the rest of the body. The bacteria can persist in granulomas for many years as a latent TB infection.

Tuberculosis is difficult to identify because routine tests do not pick up Mtb. This disease requires an examination by an infectious disease or lung doctor who will order specialized tuberculosis tests to detect the disease.  

Once the type of tuberculosis is identified, a treatment plan will be developed. Tuberculosis requires treatment with less common antibiotics and at least three to five different antibiotics in the beginning of treatment. 

Tuberculosis Causes

Tuberculosis (TB) is caused by the bacteria Mycobacterium tuberculosis, or Mtb. The body's response to active TB infection produces inflammation that can lead to scarring in the lungs. Sometimes the body can completely wall off and compartmentalize the bacteria in a structure called a granuloma. If this granuloma breaks down or isn’t able to form completely, then a person can become ill with TB.  

How TB Is Spread

Tuberculosis is a contagious or infectious disease. 

• It is spread from person to person. 
• You can become infected by inhaling the germs. 
• Germs are sprayed into the air when someone with the active disease coughs.
• Tuberculosis can spread easily in crowded living and working conditions. 
• People who have weakened immune systems have a higher risk for developing TB.

Inhaling TB germs does not mean you will develop active disease. A person's natural body defenses are often able to control the infection so that it does not cause disease. In many cases, people are infected do not have active disease. Only about 5-10% of those infected develop active TB over their lifetime.

TB Cases in the U.S.

In the United States, TB had been steadily declining for decades and then abruptly dropped during the COVD-19 pandemic. Every year since 2022, there have been an increasing number of TB cases in the U.S. To learn more about the latest data on TB in the U.S., visit the Centers for Disease Control and Prevention TB website.  

In the U.S., people most impacted by TB have lived outside of the U.S. in a TB-endemic area of the world. Areas of the world that are impacted by political disruption, stark income inequality and limited access to health care are also areas most impacted by TB.  It is estimated that nearly one third of the world’s population may be infected with TB. An estimated 10 million people fall ill with TB each year. The 2023 World Health Organization’s Global TB report estimates that the number of TB deaths around the globe in 2022 was 1.3 million.

Types of TB

Active TB Disease

Active tuberculosis is an illness in which TB bacteria are rapidly multiplying and invading different organs of the body. The typical symptoms of active TB can include: 

• Cough.
• Sputum/mucus production.
• Fatigue.
• Weight loss.
• Fever, chills and sweating at night. 

It is rare that someone with TB can have chest pain or cough up blood. A person with active pulmonary TB disease may spread TB to others by airborne transmission of infectious particles coughed into the air.

Latent TB Infection

Many of those who are infected with TB do not develop the active version of the disease. They have no symptoms and their chest X-ray may be normal. The only sign may be a reaction to the tuberculin skin test (TST) or interferon-gamma release assay (IGRA). However, there is always a risk that the latent infection may escalate to active disease. The risk is increased by other illnesses such as HIV or medications which compromise the immune system. To protect against this, many public health programs and health care providers offer preventive therapy or treatment for latent TB infection.

The Centers for Disease Control (CDC) estimates there are 13 million people living in the U.S. with a latent TB infection. Latent TB can remain dormant for decades before progressing to active TB.