Tuberculosis (TB) can transmit via the air, and the risk of infection depends on several factors. These can include the duration of exposure, proximity to a person with the infection, and immune system health.

TB is an infectious disease that occurs due to Mycobacterium tuberculosis (M. tuberculosis). This bacterium primarily affects the lungs.

Not everyone who acquires TB bacteria will become unwell. As a result, two TB-related conditions exist: latent TB infection and TB disease. With the former, a person has M. tuberculosis bacteria in their body but does not have symptoms. The latter occurs when the infection overcomes the immune system and the bacteria starts replicating. At this stage, a person often develops symptoms.

If a person suspects TB exposure, they should contact a doctor.

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TB spreads through the air when a person with an active TB infection coughs, sneezes, or talks. This releases small droplets that contain bacteria. If another person inhales the droplets, they can acquire a TB infection.

However, exposure to the TB bacteria does not necessarily mean a person will acquire the infection. Several factors can affect the likelihood of contracting the disease after exposure. These can include the following:

  • Duration: On average, it takes 8 hours or more of exposure for enough bacteria to build up in a person’s body for them to be at risk of developing TB.
  • Proximity: Living in the same household or sharing a workspace with a person with an active TB infection raises the risk of transmission.
  • Immune system health: People with a weakened or compromised immune system are at the highest risk of developing TB.
  • Different strains of bacteria: Diverse strains of TB means some are more virulent than others.

Suspected or known exposure to TB requires prompt action. In these instances, a person should seek medical evaluation. By contacting a healthcare professional, they will be able to assess risk factors and order the appropriate tests.

Typically, a doctor will assess for TB symptoms and request a chest X-ray. If a person has symptoms or the X-ray suggests active TB, the doctor will then request a sputum test.

If a person has no symptoms and the X-ray does not indicate active TB, a doctor may order other tests to identify latent TB. This may either be a skin test or a blood test.

Some people develop TB disease within a few weeks of exposure to it. In other cases, a person may not become unwell for several years until they experience a weakening of their immune system.

After exposure to TB bacteria, it may take some time before symptoms or signs of infection become apparent. This period is known as the incubation period. A 2018 review suggests that the average incubation ranges between several months and 2 years.

Not everyone will develop active TB disease following exposure to TB bacteria. A latent TB infection refers to when the immune system can fight the bacteria to stop them from growing. In these people, the TB bacteria remain inactive without causing disease.

People with latent TB have no symptoms and TB cannot spread from them to others. However, if they do not receive preventative treatment, they may develop active TB disease.

If the immune system cannot prevent TB from multiplying, a person may develop active TB disease. This describes when they become unwell and TB bacteria can transmit from them to others.

Detecting a TB infection early is crucial for effective management. A healthcare professional may undertake the following methods for TB detection:

  • Tuberculin skin test: This involves injecting a small amount of purified protein derivative into the skin of the forearm. A healthcare professional then examines the injection site after 48–72 hours. A positive reaction indicates a TB infection.
  • Interferon-Gamma Release Assays (IGRAs): Blood tests known as IGRAs measure the immune response to TB-specific proteins. The two IGRAs available in the United States are QuantiFERON-TB Gold and T-SPOT.TB.
  • Chest X-ray: If a doctor suspects a TB infection, a chest X-ray can reveal lung changes associated with active TB disease. Typically, a doctor will perform this in combination with other methods, as X-ray alone cannot confirm whether a person has active TB disease.
  • Sputum testing: For suspected active TB disease, a healthcare professional can take a sample of sputum (mucus coughed up from the lungs) and test it to identify the presence of TB bacteria.

Taking steps to help prevent TB is important for managing the spread of the disease. Some examples of preventive measures include:

  • TB vaccination: Some countries use the Bacille Calmette-Guérin vaccine to protect against TB, primarily in children. However, its effectiveness varies, and it is less common within the U.S.
  • Avoiding close contact: A person should try to limit exposure to individuals with active TB disease. This is particularly important for people with weakened immune systems. If a person must be around someone with active TB, they should consider wearing a mask and try to maintain good ventilation in the area.
  • Latent TB treatment: For a confirmed latent TB infection, a person should follow a healthcare professional’s recommendations for treatment to help prevent its progression to active TB disease.

Treatment for TB depends on whether it is active or latent.

Treatment for active TB involves a combination of antibacterial medications. Depending on the treatment regimen, a person may need to take medications for 4, 6, or 9 months. If the first line of drugs does not produce the required results, the regimen will last longer.

Common medications include isoniazid, rifampin, ethambutol, and pyrazinamide. It is crucial for a person to adhere to the prescribed treatment regimen to help prevent drug resistance.

Treatment regimens for latent TB infections include isoniazid, rifapentine, and rifampin. The length of the treatment will depend on the regimen a doctor recommends, which may last 1, 3, or 4 months for a shorter course or 6–9 months for a longer course.

TB is an infectious disease. Exposure to TB can occur through inhaling droplets from a person with an active infection. Various factors influence the likelihood of contracting TB after exposure. If a person suspects exposure, they should seek medical evaluation.