Latent Tuberculosis

Latent tuberculosis means you carry tuberculosis bacteria in your body, but they are inactive and cannot make you sick or spread to others. However, without treatment, these sleeping bacteria can wake up and cause active disease.

Table of contents

• What is Latent Tuberculosis?
• How Infection Occurs
• How Common is Latent Tuberculosis?
• Differences Between Latent and Active TB
• Who is at Risk?
• How is Latent TB Diagnosed?
• Risk of Developing Active Disease
• Treatment Options
• Why Treatment is Important

What is Latent Tuberculosis?

Latent tuberculosis infection, also called LTBI or inactive TB, occurs when you have tuberculosis bacteria in your body that are alive but not active^[1]. The bacteria, called Mycobacterium tuberculosis, are present but remain dormant, like they are sleeping^[3].

When you have latent TB, you do not feel sick and have no symptoms^[1]. You cannot spread the bacteria to other people because the bacteria are not actively growing^[1]. Your body’s immune system keeps the bacteria under control by forming a barrier around them^[1].

latent TB infection, LTBI, inactive TB, latent tuberculosis infection

How Infection Occurs

TB infection happens when you breathe in tuberculosis bacteria that reach the deepest parts of your lungs^[1]. Most of these bacteria are destroyed or stopped by your body, but a small number may enter your bloodstream and spread throughout your body^[1].

• Lungs
• Lymph nodes
• Kidneys
• Brain
• Bone

Within two to eight weeks after breathing in the bacteria, special immune cells called macrophages surround and contain the bacteria^[1]. These cells form a protective shell called a granuloma that keeps the bacteria trapped and under control^[1]. This is the state known as latent TB infection.

You cannot catch TB from someone with latent tuberculosis^[2]. TB only spreads when someone has active TB disease in their lungs and coughs, sneezes, or speaks, releasing tiny droplets containing bacteria into the air^[2]. These droplets can remain suspended in the air for several hours depending on the environment^[2].

How Common is Latent Tuberculosis?

Latent tuberculosis is very common worldwide. As of 2023, approximately one-quarter of the world’s population has latent or active TB^[2][3]. In the United States alone, an estimated 13 million people have latent TB infection^[1].

The distribution of TB infection is uneven around the world^[2]. In many Asian and African countries, approximately 80% of the population tests positive for TB infection^[2]. In contrast, only 5 to 10% of people in the United States test positive^[2].

Statistics show that approximately one-third of people exposed to someone with active pulmonary TB become infected with the bacteria^[2]. However, only one in ten of these infected people will develop active TB disease during their lifetime^[2].

Differences Between Latent and Active TB

There are important differences between latent TB infection and active TB disease. Understanding these differences helps explain why treatment for latent TB is so important.

People with latent TB have several key characteristics. They have a small number of TB bacteria in their body that are alive but inactive^[1]. They cannot spread TB bacteria to others and do not feel sick^[1]. Their TB blood test or skin test results are usually positive, indicating TB infection^[1]. However, their chest X-rays are typically normal, and their sputum tests are negative^[1]. They do not require respiratory isolation^[1].

In contrast, people with active TB disease have bacteria that are awake and multiplying^[9]. They usually have symptoms that make them feel unwell, and if the TB is in their lungs, they can pass the disease to others^[9]. Active TB shows up on chest X-rays when it affects the lungs^[9].

Who is at Risk?

Certain people have a higher risk of being exposed to TB and developing latent infection. You might be at higher risk for TB exposure if you are a resident or employee in group settings where TB can spread, such as jails, hospices, skilled nursing facilities, or shelters^[1]. Healthcare workers, especially those working in TB laboratories, also face increased exposure risk^[1].

People who have lived in regions where TB is common, including Latin America, the Caribbean, Africa, Asia, Eastern Europe, and Russia, are at higher risk^[1]. Anyone who has been in close contact with someone known or suspected to have TB disease is also at increased risk^[1].

Some people are more likely than others to have their latent TB progress to active disease. People with weakened immune systems are at considerably higher risk^[9]. This includes people who inject intravenous drugs, have kidney disease, diabetes, or other chronic illnesses, have received an organ transplant, or are on chemotherapy treatment for cancer^[1].

Those with untreated HIV infection face especially high risk of developing active TB disease^[9]. Babies, young children, and elderly people are also more vulnerable^[7].

How is Latent TB Diagnosed?

Latent TB has no symptoms, so it can only be detected through specific tests^[1]. The main ways to diagnose latent TB are through placing a tuberculin skin test on the forearm or getting a TB blood test, along with obtaining a chest X-ray if either test is positive^[7].

The tuberculin skin test, also called the Mantoux test or TB skin test, involves injecting a small amount of fluid under the skin of your forearm^[1]. You must return to have the test read 48 to 72 hours later. A raised, hard bump at the injection site may indicate TB infection.

TB blood tests, called interferon-gamma release assays or IGRAs, measure how your immune system reacts to TB bacteria^[3]. These tests require only one visit and are not affected by prior BCG vaccination^[1].

If you have a positive TB test, you will typically have a chest X-ray to make sure you do not have active TB disease^[7]. People with latent TB have normal chest X-rays^[1][9]. Your doctor may also ask about symptoms and examine you to rule out active disease.

Risk of Developing Active Disease

Without treatment, about 5 to 10% of people with latent TB infection will develop active TB disease at some point in their lives^[1][9]. About half of those who develop TB will do so within the first two years of infection^[9].

The latent TB bacteria can wake up if your immune system becomes weakened^[1]. When the bacteria overcome your body’s defenses and begin to multiply, latent TB progresses to active TB disease^[9]. This can happen many years after you first breathe in TB bacteria^[6].

Progression from untreated latent TB infection to active TB disease accounts for approximately 80% of TB cases in the United States^[1][10]. This makes latent TB infection the largest reservoir for potential TB transmission. Finding and treating people with latent TB is essential for controlling and eliminating TB disease^[1][10].

Treatment Options

Latent TB infection can be treated with antibiotic medicines to prevent it from becoming active disease^[1]. Treatment kills the sleeping TB bacteria before they can make you sick^[5]. Several treatment options are available, and your doctor will help you choose the best one for your situation.

The preferred treatments are short-course regimens that use medicines from the rifamycin family^[10]. These include taking isoniazid plus rifapentine once weekly for three months, taking rifampin daily for four months, or taking isoniazid plus rifampin daily for three months^[10].

Alternative treatments include taking isoniazid alone daily for six to nine months^[10]. The shorter regimens with rifamycin-based medicines are generally preferred because they are effective, safe, and more people complete the full course of treatment^[10].

It takes many months for the medicine to kill the TB bacteria because they are very strong^[5][14]. It is very important to take your medicine exactly as your doctor tells you and to complete the full course of treatment^[5]. If you miss too many doses or stop taking medicine early, the treatment might not work^[5].

Some people may have side effects from the medicines. Common side effects can include upset stomach, headache, skin rash, or changes in how your urine or other body fluids look^[5][15]. Most people take the medicine without serious problems. If you experience any side effects, tell your doctor or nurse right away^[5].

You should avoid drinking alcohol while taking treatment for latent TB, as it can interact with the medicine and cause side effects^[5][14]. Tell your doctor about any other medicines you are taking, as some TB medicines can affect how other medications work^[5][10].

Why Treatment is Important

Treatment for latent TB infection is effective at preventing TB disease^[1]. Even though you do not feel sick with latent TB, treatment is still very important. Sleeping TB bacteria are much easier to kill before they wake up and make you sick^[5][14].

About one in ten people with latent TB will develop active TB disease at some point^[6][15]. There is no way to know if you will be one of them^[6]. Treatment is the only way to remove the TB bacteria from your body^[6].

Active TB disease is serious and can be life-threatening if not treated^[4]. It requires treatment with at least four medicines for at least six months^[4]. Latent TB treatment is usually shorter and involves fewer medications^[6]. These are good reasons to treat the latent TB bacteria while you are healthy and before they have a chance to wake up^[6].

Treating latent TB also protects your family and community. By preventing your infection from becoming active disease, you eliminate any future risk of spreading TB to others^[5].

If you have received the BCG vaccine, you should still take medicine for latent TB if you test positive^[5][14]. BCG protects children from severe forms of TB but only for a few years^[5]. It cannot protect against latent TB infection or active TB disease later in life^[5].

If you complete your treatment as prescribed, your risk of developing active TB is much lower^[15]. However, it is possible you could breathe in TB bacteria again in the future if exposed to someone with active disease^[15]. The chances of this are low for most people, but it is useful to know the common symptoms of active TB so you can see your doctor if you develop a cough lasting three weeks or longer, fever, night sweats, weight loss, loss of appetite, or tiredness^[15].