Tuberculosis spreads through the air when an infected person coughs, sneezes, or speaks

You get tuberculosis (TB) by breathing in bacteria called Mycobacterium tuberculosis that another person releases into the air. This happens when someone with active TB disease in their lungs or throat coughs, sneezes, speaks, or sings. The bacteria travel in tiny droplets that float in the air for hours. If you breathe in those droplets, the bacteria can lodge in your lungs and start an infection.

Not everyone who breathes in TB bacteria gets sick. Your immune system may kill the bacteria before it takes hold, or the infection may stay dormant in your body for years or your whole life. Whether you develop active TB disease depends on your age, overall health, and how strong your immune system is at the time of exposure.

Key Takeaways

  • TB spreads through airborne droplets when someone with active lung or throat TB coughs, sneezes, or speaks.
  • You cannot get TB from touching someone, sharing food or drinks, or shaking hands — the bacteria must reach your lungs.
  • Most people who breathe in TB bacteria do not develop active disease because their immune system controls the infection.
  • People with weakened immune systems, including those with HIV, are much more likely to develop active TB after exposure.
  • TB is not spread by casual contact in public spaces; close, prolonged contact with an infected person is usually needed.

Who is most likely to develop active TB after exposure

Your risk of developing active TB disease after breathing in the bacteria depends mainly on the strength of your immune system. People with HIV, especially those with a CD4 count below 200, have the highest risk — they are about 20 times more likely to develop active TB than people without HIV. People with diabetes, chronic kidney disease, or those taking medications that suppress the immune system (like TNF inhibitors for rheumatoid arthritis) also face higher risk.

Age matters too. Infants and very young children have immune systems that are not yet fully developed, so they are more likely to develop severe TB disease quickly. Older adults whose immune systems have weakened over time also face higher risk. People who are malnourished or who misuse alcohol or drugs have weaker immune responses and are more vulnerable to active disease.

The difference between TB infection and TB disease

Being exposed to TB bacteria does not automatically mean you have TB disease. When you first breathe in the bacteria, you may develop latent TB infection — the bacteria are in your body but your immune system is holding them in check. You have no symptoms, you cannot spread TB to others, and you may never know you were infected unless you get tested.

If your immune system cannot control the bacteria, you develop active TB disease. This usually happens within the first two years after infection, but it can happen decades later if your immune system weakens. With active TB disease, you have symptoms like a persistent cough, chest pain, fever, and night sweats. You can spread TB to others, and without treatment the disease can damage your lungs and spread to other organs.

How long you need to be around someone with TB to get infected

There is no fixed rule for how much exposure leads to infection — it depends on how contagious the infected person is, how well-ventilated the space is, and how long you spend together. Generally, close contact over hours or days carries more risk than brief encounters. Sitting across from someone with active TB in a well-ventilated room for a few minutes is lower risk than sharing a bedroom or spending eight hours in a car with them.

People with TB disease in their lungs are most contagious in the first two to three weeks after symptoms start, before they begin treatment. Once someone has been on TB medication for about two weeks, they usually stop spreading the disease to others. TB in other parts of the body — like the lymph nodes or bones — is not contagious because the bacteria are not in the lungs or throat.

Places where TB transmission is more likely

TB spreads more easily in crowded, poorly ventilated indoor spaces where people spend extended time together. Homeless shelters, prisons, nursing homes, and hospitals have higher rates of TB transmission because people live or work in close quarters with limited fresh air circulation. Households where someone has active TB disease carry significant risk — family members who share a bedroom or spend many hours together are at higher risk than casual visitors.

Workplaces with good ventilation and where people do not spend prolonged time in close contact carry lower risk. Public spaces like buses, stores, or restaurants are not typical settings for TB transmission because the contact is brief and the space is usually larger. Healthcare workers who care for TB patients without proper respiratory protection face higher risk, which is why hospitals use isolation rooms with special air handling for TB patients.

What does not spread TB

You cannot get TB from touching someone's skin, shaking hands, or hugging. TB bacteria do not survive on skin or in saliva. You cannot get TB from sharing food, drinks, utensils, or a toothbrush, because the bacteria are killed by stomach acid if swallowed. You cannot get TB from sharing a toilet, bathtub, or shower. You cannot get TB from someone's sweat, blood, or urine unless those fluids somehow enter your lungs — which is extremely rare and not a realistic transmission route.

You also cannot get TB from animals, except in very rare cases from unpasteurized milk that contains TB bacteria from infected cattle. Modern milk is pasteurized, which kills the bacteria. TB is a human disease spread between people through the air, not through casual contact or contaminated objects.

What happens after you are exposed to TB

If you have been in close contact with someone who has active TB disease, you should get tested. A doctor can order a tuberculin skin test (also called a Mantoux test) or an interferon-gamma release assay (IGRA) blood test. These tests show whether TB bacteria are in your body, but they cannot tell the difference between latent infection and active disease — that requires a chest X-ray and sometimes other tests.

If you test positive for TB infection and have no symptoms, you may be offered preventive therapy — usually a course of antibiotics taken for several months. This treatment kills the bacteria before active disease can develop. If you test positive and have symptoms like a cough lasting more than three weeks, fever, or night sweats, you need further testing and treatment for active TB disease. Starting treatment early prevents serious illness and stops you from spreading TB to others.

Frequently Asked Questions

Can you get TB from someone who is on treatment?

Once someone has been taking TB medication for about two weeks, they are usually no longer contagious. However, if someone stops taking their medication early or does not take it as prescribed, they can become contagious again. If you were exposed before they started treatment, you should still get tested.

What if I was exposed but do not have symptoms?

You may have latent TB infection, which means the bacteria are in your body but your immune system is controlling them. You have no symptoms and cannot spread TB to others. A skin test or blood test can show whether you were infected. If positive, a doctor may recommend preventive treatment to stop active disease from developing later.

How soon after exposure do TB symptoms appear?

If you develop active TB disease, symptoms usually appear within the first two years after infection. However, TB can stay dormant for decades and become active later if your immune system weakens. This is why people exposed to TB are tested even if they feel fine.

Can you get TB from eating food prepared by someone with TB?

No. TB bacteria are killed by stomach acid, so swallowing them does not cause infection. TB spreads only through the air when bacteria from the lungs or throat are inhaled. Food prepared by someone with TB is safe to eat.

Is TB more contagious than the flu?

TB spreads less easily than the flu. You need closer, longer contact with someone who has active TB to become infected. However, TB is much more serious — it can cause permanent lung damage and death if untreated, while most people recover from the flu without treatment.