Latent tuberculosis: All you need to know

Latent tuberculosis is a condition that requires careful special medical attention to prevent progression to active tuberculosis.

This article provides an expert insight into the mechanisms of latent tuberculosis, its diagnosis, and current strategies for treatment and monitoring.

What is latent tuberculosis?

Latent tuberculosis occurs when a person is infected with the bacterium Mycobacterium tuberculosis but doesn’t show symptoms of the disease. In this state, the bacteria remain dormant in the body and don’t cause illness. As a result, latent tuberculosis isn’t contagious.

On the other hand, active tuberculosis occurs when the bacteria become active in the body, multiplying and causing symptoms such as a persistent cough, fever, weight loss, and fatigue. Unlike latent tuberculosis, active tuberculosis is contagious and can spread from person to person through respiratory droplets when an infected individual coughs or sneezes.

However, there is a risk for latent tuberculosis to progress to an active form, and this risk is higher in people with weakened immune systems, such as people living with HIV/AIDS, diabetes, or people receiving immunosuppressive treatments.

How is latent tuberculosis diagnosed?

Diagnosing latent tuberculosis firstly involves tests that detect the presence of Mycobacterium tuberculosis bacteria in the body. The first primary diagnostic tools are:

• Tuberculin skin test: This test injecting a small amount of tuberculin protein under the skin of the forearm. After 48 to 72 hours, the area is examined for swelling. A positive reaction suggests tuberculosis infection.
• Interferon-gamma release assays (IGRAs): For example, the QuantiFERON-TB Gold test or T-SPOT.TB. These are blood tests that measure the immune system’s response to Mycobacterium tuberculosis bacteria. A positive result indicates tuberculosis infection.

Subsequently, further evaluation is then needed to determine if the infection is latent or active. This usually involves a detailed medical history, physical examination, and a chest X-ray to check for signs of active tuberculosis. In some cases, additional tests such as sputum analysis may be required.

Do I need treatment for latent tuberculosis?

Yes, treatment for latent tuberculosis is highly recommended, especially for people at high risk of reactivation to active tuberculosis. The most commonly used regimens are:

• Isoniazid: Taken daily for 6-9 months, this medication is effective in killing dormant Mycobacterium tuberculosis bacteria.
• Rifampin: An alternative to isoniazid, rifampin is taken daily for 4 months.
• Isoniazid and rifapentine: A shorter regimen that involves taking both medications once weekly for 12 weeks under direct observation.

During treatment, it’s crucial to follow the prescribed regimen closely to ensure its effectiveness. Skipping doses or stopping treatment prematurely increases the risk of developing drug-resistant tuberculosis.

How is latent tuberculosis monitored?

People with latent tuberculosis generally don’t experience any symptoms or lung damage. Therefore, the condition doesn’t typically affect lung function or lead to other respiratory issues. However, if latent tuberculosis reactivates and progresses to active tuberculosis, it can cause significant pulmonary complications, such as chronic cough, lung tissue damage, and difficulty breathing.

To minimise this risk, people undergoing treatment for latent tuberculosis will require periodic liver function tests, especially if they are taking isoniazid. Regular follow-up with a chest (respiratory medicine) specialist will help ensure lung health is maintained and the condition remains controlled.

If you suspect you have been exposed to tuberculosis or have tested positive for the infection, it’s important to consult a respiratory medicine specialist. Early intervention can minimise the impact of tuberculosis on your health.