What is Latent Tuberculosis Infection (LTBI)?

LTBI, or Latent Tuberculosis Infection, isn’t a term that we hear every day. Essentially, it describes a state where a person carries the Mycobacterium tuberculosis bacteria in their body but does not show any symptoms of the disease – Tuberculosis. In this state, the bacteria exist in a dormant form, unable to cause harm or spread to others.

Although this might sound a bit alarming, it’s important to note that LTBI is a natural response of our immune system. When the tuberculosis bacteria enter our bodies, our immune cells surround them, keeping them locked away and unable to cause disease. And as long as our immune system remains strong, these bacteria can remain inactive for a lifetime. Quite a truce, isn’t it?

The Difference Between Latent Tuberculosis Infection and Active TB

The critical difference between LTBI and active TB lies in their impact on our health and others around us. Active TB is a serious illness that primarily affects the lungs, but it can also impact other parts of the body such as the kidneys, brain, and spine. Symptoms include a chronic cough, chest pain, weight loss, fatigue, fever, night sweats, and loss of appetite.

Most importantly, active TB is contagious, which means it can spread from person to person through tiny droplets released into the air via coughs or sneezes. LTBI, on the other hand, presents no symptoms, does not make the person feel sick, and is not contagious. But the caveat is that it can develop into active TB if not addressed properly.

Diagnosing Latent Tuberculosis Infection

Just as an archaeologist uncovers hidden artefacts, our healthcare system has methods to unearth hidden TB bacteria. The two primary diagnostic tools are the Tuberculin Skin Test (TST) and Interferon Gamma Release Assays (IGRAs).

Tuberculin Skin Test (TST)

Think of the TST as an investigative detective that uncovers whether our bodies have had a previous encounter with the TB bacteria. It involves injecting a small amount of a substance called tuberculin into the skin on the lower part of your arm. After 48-72 hours, a healthcare professional checks the reaction on your skin. If your immune system recognises the tuberculin, it will respond by causing a bump at the injection site, a bit like the body’s way of saying, “Hey, I’ve met this guy before!”

Interferon Gamma Release Assays (IGRAs)

IGRAs, on the other hand, are like our health system’s private investigators. They are blood tests that measure the immune system’s response to TB bacteria.


The T-SPOT.TB test is one type of IGRA. It’s as precise as counting the number of guests at a party. The test directly counts the number of blood cells that react to TB bacteria in a blood sample.

QuantiFERON-TB Gold Test

Then we have the QuantiFERON-TB Gold test. This one measures the level of an immune response to the bacteria in the blood. Rather than counting individual cells, it measures the concentration of a specific protein released by the cells in response to the bacteria – a bit like gauging the overall noise level at the party!

The Epidemiology of Latent Tuberculosis Infection

Prevalence Globally

Let’s step back for a moment and look at the bigger picture. The World Health Organization estimates that approximately one-fourth of the world’s population has LTBI. That’s nearly 2 billion people! But don’t let that alarm you. Only 5-10% of people with LTBI will develop active TB disease in their lifetime. However, this risk is significantly higher among people with compromised immune systems, such as those living with HIV or those undergoing specific types of medical treatments.

Prevalence in the UK

In the UK, the overall prevalence of LTBI is lower than the global average, reflecting the success of the national TB control programme. However, there are some groups who are at a higher risk, particularly those in urban areas, those from low-income backgrounds, and those who have immigrated from countries with high TB prevalence.

Treating Latent Tuberculosis Infection

Who Needs Treatment for LTBI?

Not everyone with LTBI needs treatment. But certain groups with a higher risk of progressing to active TB should consider it. These include people with HIV, those who have been recently exposed to TB (like living in the same house with someone who has active TB), and those with certain medical conditions or lifestyle factors that weaken the immune system. Also, healthcare workers and those who work or reside in high-risk settings like prisons and nursing homes should consider treatment.

Treatment Regimens Used in LTBI

Treatment for LTBI aims to kill the dormant bacteria and prevent them from becoming active.

Isoniazid (INH)

Isoniazid, often abbreviated as INH, is the most common medication used for LTBI. It is generally taken daily for 6 to 9 months. This treatment can significantly reduce the risk of developing active TB, especially when taken correctly and completed in full.

Rifampin (RIF)

Another medication used in LTBI treatment is Rifampin, or RIF. This medicine is usually taken once daily for 4 months, and it’s an effective alternative for those who cannot tolerate isoniazid or for whom isoniazid isn’t recommended.

Isoniazid qnd Rifampicin (INH/RIF)

The combination of Isoniazid and Rifampicin (INH/RIF) can be adminstered daily for a total of 3 months, reducing the duration of treatment further.

Isoniazid and Rifapentine (INH/RPT)

Finally, there’s a combination regimen of Isoniazid and Rifapentine (INH/RPT). This dynamic duo only needs to come into play once a week for 12 weeks and is administered under direct observation. This regimen is not only shorter but also easier to complete, making it a convenient alternative.


Understanding LTBI is a crucial aspect of our fight against TB. By comprehending what LTBI is, how it’s diagnosed, and how it’s treated, we can contribute to eradicating TB on a global scale. So, let’s continue to spread the word and encourage those at risk to get tested.

Frequently Asked Questions

Q1: Can a person with LTBI spread the disease?

A1: No, a person with LTBI is not contagious because the bacteria are dormant and are not released in coughs or sneezes.

Q2: Is it necessary for everyone with LTBI to get treatment?

A2: Not everyone. Treatment is recommended for people at high risk of developing active TB. A respiratory infection specialist can help assess this risk.

Q3: What’s the goal of treating LTBI?

A3: The primary goal of treating LTBI is to eliminate the dormant TB bacteria in the body and prevent the development of active TB disease.

Q4: Are there side effects to LTBI treatment?

A4: Yes, like all medicines, LTBI treatments can have side effects. These can range from mild ones, such as nausea, to more severe ones, like liver damage. It’s crucial to discuss these potential side effects with your treating respiratory infection specialist.


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Disclaimer: The information provided in this article is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your healthcare provider with any questions you may have regarding a medical condition or treatment

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