How Tuberculosis Spreads: Inactive TB, Active TB Disease and Who Is at Risk

Tuberculosis (TB) is caused by a bacterium, Mycobacterium tuberculosis. Breathed in, the germs can settle in the lungs and grow, and from there travel through the blood to other parts of the body, such as the kidneys, spine and brain.

CDC

Inactive TB and active TB disease

Some people get sick within weeks of infection, before their immune system can fight back; others get sick years later, when their immune system weakens for some other reason.

How it spreads

When someone with active TB of the lungs or throat coughs, speaks or sings, germs get into the air — where they can linger for several hours, depending on the setting. People nearby can breathe them in and become infected. Spread is more likely indoors or where air circulates poorly (such as a closed vehicle) than outdoors.

TB germs spread through the air. CDC

TB does not spread by:

• shaking hands;
• sharing food or drink;
• touching bed linens or toilet seats;
• sharing toothbrushes;
• kissing.

TB in other parts of the body, such as the kidney or spine, is usually not infectious. People with active TB are most likely to infect family, friends, co-workers and classmates.

Who's at higher risk

Of being exposed, if you:

• were born in or often travel to countries where TB is common, including some in Asia, Africa and Latin America;
• live or have lived in group settings where TB is more common — homeless shelters, prisons or jails;
• recently spent time with someone with active TB;
• work where TB is more likely to spread.

Of getting sick once infected, if you:

• were recently infected;
• have a weakened immune system from certain medicines or conditions such as diabetes, cancer or HIV.

More: TB risk factors.

What to do

• Inactive TB? Treating it is the best way to prevent active disease — especially important for people with weakened immune systems.
• Active TB of the lungs or throat? You may be infectious. Your provider will tell you how to protect others — such as covering coughs with a tissue or staying home from work or school. After a few weeks of treatment, you'll feel better and may no longer be infectious. See preventing TB.
• Think you've been exposed? Ask your provider or health department about a TB blood test or skin test, and tell them when you were with the person who has TB.

More: Questions and Answers About TB · What You Need to Know About TB · Think. Test. Treat TB.

Sources

Based on "Tuberculosis: Causes and How It Spreads," Centers for Disease Control and Prevention; a work of the United States government in the public domain.