What Is Latent TB?

Medically reviewed by Jordana Haber Hazan, MD

While infection from tuberculosis (TB) bacteria can affect lung function and cause serious symptoms, there are no apparent signs for many. Without symptoms, this infection is known as latent TB; it can only be detected with clinical testing, and unlike its active counterpart, it's not contagious.

While approximately 90% to 95% of latent cases never develop into active TB, it can be a risk, especially for those with weakened immune systems.

This article provides an overview of latent TB and discusses this condition's causes, diagnosis, treatment, and prognosis.

Types of TB Infection

There are two types of TB infection: active, symptomatic cases, and latent TB. Key differences include:

• Bacterial load: The infectious bacteria responsible for TB multiplies, and symptoms become present once the immune system can no longer fight them off. In latent TB cases, there are only trace amounts of bacteria, and they don’t grow or spread.

• Symptoms: Active TB causes a distinct set of troubling symptoms, most affecting the lungs. These include chest pains, coughing blood, persistent cough, chills, and weight loss. By definition, latent TB causes no physical signs or symptoms (asymptomatic).

• Transmission: TB spreads via droplets in the air from a person with symptoms. However, those with latent TB can’t spread the disease.

• Diagnosis: Latent TB causes antigens to be released in the blood, which can be detected with clinical testing. Signs of active cases are also seen in chest X-rays and by testing saliva.

A Common Condition

Though most cases of TB don’t become symptomatic, this infection is prevalent worldwide. Around 23% to 32% of the world's population is affected.

Latent TB Symptoms

When a TB infection is symptomatic, it causes chest pains, a persistent cough, and blood or phlegm to come up while coughing, among other issues. However, latent TB doesn’t cause any of these symptoms. This is because the immune system can prevent the infecting bacteria from growing and spreading.

Learn More: Symptoms of Tuberculosis (TB)

Causes

TB arises due to infection by the Mycobacterium tuberculosis bacterium. It’s spread when droplets in the air—expelled when an infected person coughs, talks, or sings—are inhaled. As such, close proximity to a person who’s sick and regular contact with them can get you sick. Physically touching someone, sharing foods or drinks, touching shared surfaces, like toilet seats or counters, and even kissing won’t lead to transmission.

In active TB, symptoms arise as the bacterium spreads in the lungs and throat, but the immune system effectively manages this spread in latent cases. However, cases can become symptomatic if immunity is weak or weakened. Risk factors for this progression include:

• Being an infant or young child

• Human immunodeficiency virus (HIV) or AIDS

• Organ transplant

• Late-stage kidney disease

• Cancers of the blood (leukemia, lymphoma, and multiple myeloma, among others)

• Taking immunosuppressive drugs or corticosteroids

Who Should Get Screened for TB?

Those who are at a higher risk of being infected with TB bacteria should be tested for TB. This includes people who:

• Have spent time with someone who has TB

• Are from a country where TB is more prevalent

• Live or work in high-risk settings (homeless shelters, hospitals or healthcare settings, correctional facilities)

• Are infants, children and adolescents exposed to at-risk adults

Speak with your healthcare provider about your circumstances to determine whether you should be tested for TB.

Diagnosis

Since latent TB doesn’t cause symptoms, clinical diagnosis is the only way cases are caught. Several tests are used to detect TB infections and evaluate their progress. These include:

• Medical evaluation: Based on physical examination and assessment, those with latent TB won’t show any outward signs of the condition. To help with diagnosis, you’ll be asked about your medical history and any medications you’re taking.

• TB skin test: The TB skin test requires two visits to your caregiver. In the first appointment, a special fluid, tuberculin, is injected into the lower part of the arm. This causes the injected area to become hardened and rise. This area is evaluated in a second office visit after 48 to 72 hours, with its size and attributes indicating the presence of infection. This skin test can isolate both latent and active cases.

• TB blood test: As the immune system combats TB, it releases antigens, which can be detected in the bloodstream. In the United States, two specific tests are used: the QuantiFERON-TB Gold Plus (QFT-Plus) and the T-SPOT TB (T-Spot), both of which require blood samples to send to a clinical laboratory. Blood tests detect both latent and active cases.

• Chest X-ray: While abnormal results aren’t seen in latent TB, chest X-ray can detect the progression of active forms in the lungs. The presence of lesions can be a sign of infection, though this, alone, isn’t definitive of diagnosis.

• Sputum (saliva) smear: The sputum smear is another test that will detect many active cases but not isolate a latent case. This involves clinical assessment of a saliva sample, with positive results helping to confirm a diagnosis.

Treatment

While latent TB doesn’t cause health problems, it does raise the risk of developing an active case. Not only can treatment prevent this progression, but it also helps control the spread of this disease. Treatment typically involves taking antibiotics over prolonged periods. Common approaches include:

• Rifampin (RIF): RIF is taken daily for four months for latent TB.

• Isoniazid (INH): Derivations of INH are taken either daily or twice weekly for courses of six or nine months.

• INH and rifapentine (RPT): A combination therapy, INH and RPT, is taken once weekly for three months.

• INH and RIF: This combination is taken daily for three months.

Learn More: How Tuberculosis (TB) Is Treated

Prognosis

Ultimately, only a small proportion of latent TB cases become active. Researchers have found that 5% to 10% of those infected develop symptoms within two to five years of exposure. People can live their whole lives carrying this infection without experiencing any issues.

However, TB infections can become severe if left untreated, leading to death in around 45% of cases. Current treatment approaches are highly effective in preventing active TB, and therapies can effectively manage and cure the condition.

Summary

Latent TB is a type of tuberculosis infection that causes no symptoms and isn’t contagious. While some with this condition develop active TB, which causes a range of respiratory symptoms, most do not. Prolonged courses of antibiotic therapy can treat latent TB and prevent it from causing health problems.

A Word From Verywell

Latent TB is problematic because it’s silent and doesn’t cause symptoms. Though the vast majority of people with it don’t experience problems, a change in health status can lead to active TB. TB is highly treatable, and, with management, the outcomes are overwhelmingly positive; seeking help is the first step towards managing your health.

Frequently Asked Questions

Is latent TB contagious?

TB spreads through the air, arising when people inhale droplets of saliva expelled when an infected person talks, sings, or coughs. However, only those who have active symptoms are contagious. If you have latent TB, there’s no risk of others catching this condition from you.

Is it common for latent TB to become active?

Around 5% to 10% of those infected with latent TB develop symptoms within two to five years of exposure. People can carry the infection throughout their lives without ever experiencing symptoms or issues. However, TB infections can become severe if left untreated. Speak with your healthcare provider if you've spent time with someone who has TB, are at risk (live or work in a high-risk environment), or have symptoms.