Latent vs active tb

I have heard of TB, but what is latent TB?

Tuberculosis (TB) is an illness caused by bacteria. When someone with TB in their lungs coughs or sneezes, they send TB bacteria into the air. If you breathe in these bacteria, one of three things will happen:

  • your body kills off the TB bacteria so they cannot harm you now or in the future
  • the TB bacteria make you ill – this is called ‘active TB’
  • the TB bacteria remain asleep in your body – this is called ‘latent TB’.

About active TB

When people talk about TB, they tend to mean ‘active TB’. If you have active TB, the bacteria are making you ill and you might be passing TB on to other people. Active TB can be very harmful to your health, but it can be cured with a course of medicine.

About latent TB

If you have latent TB, the TB bacteria in your body are ‘asleep’. You are not ill and you cannot pass TB on to others. However, the bacteria might ‘wake up’ in the future, making you ill with active TB. The good news is that latent TB can be treated to prevent this happening.

What are the main differences between active and latent TB?

Latent TB

  • TB bacteria are asleep in your body
  • you do not have symptoms and you feel well
  • you cannot pass TB on to others
  • it can only be detected through a blood test or TB skin test

treated with one or two medicines over three to six months

Active TB

  • TB bacteria are awake and making you ill
  • you will have symptoms that make you feel unwell
  • you can pass TB to others if it is in your lungs
  • it shows up on a chest x-ray if you have TB in the lungs

treated with four or more medicines over at least six months

How does latent TB work?

Very few people fall ill immediately after they breathe in TB bacteria. If you are in good health, your immune system – your body’s defence against illness – is likely to remove all the TB bacteria that you breathe in. If it is unable to do this, it may be able to stop you from becoming ill by forcing the bacteria into a latent (sleeping) state. The bacteria are still in your body, but they are not causing damage.

However, latent TB bacteria can ‘wake up’ and become active in the future, making you ill. This can happen many years after you first breathe in TB bacteria. Latent TB bacteria are more likely to wake up if you experience lifestyle stresses or other illnesses that weaken your immune system.

Latent Tuberculosis Infection vs. Active TB Disease: What’s the Difference?

After an initial infection, the bacteria that causes TB often becomes dormant in the body. But if left untreated, it can become active and infectious.

The most common kind of TB is pulmonary tuberculosis, which affects the lungs. A latent TB infection (left) can have no symptoms, while with active TB disease (right), the bacteria multiply in the body, becoming contagious. iStock

Tuberculosis (TB) is unlike most bacterial infections in that it usually doesn’t cause symptoms immediately. Even when it starts to make you sick, symptoms come on very gradually and can often be confused with other conditions.

Most commonly, tuberculosis goes through three stages:

  • Primary TB infection
  • Latent TB infection
  • Active TB disease

Millions of people carry latent TB bacteria but never develop active tuberculosis. In fact, the Centers for Disease Control and Prevention (CDC) estimates that as many as 13 million people in the United States have a latent TB infection. (1,2,3)

About 30 percent of people who get exposed to Mycobacterium tuberculosis will develop latent TB and, if that’s left untreated, around 5 to 10 percent of those people could end up getting active tuberculosis disease at some point in their lifetime, according to a statement from the US Preventive Services Taskforce, published in September 2016 in the Journal of the American Medical Association. The number is much higher for people infected with HIV. (3,4)

Tuberculosis is more likely to enter the active phase in people who have acquired the infection recently (in the past two years). It’s also more likely to be active among those whose immune systems are weakened.

Primary or Initial Tuberculosis Infection

Infection with M. tuberculosis begins when a person breathes in airborne bacteria.

This is more likely to happen if a person is in close contact with one or more infected people with active TB who are coughing or sneezing.

In many people, any inhaled bacteria are killed immediately by the immune system. In others, the TB bacteria are surrounded by macrophages, a type of white blood cell, and enter a dormant state. This is called latent infection, and this stage can last for years or even for life. But in certain populations, including infants, the elderly, those with recently acquired TB infection, and people with weakened immune systems, symptoms of active tuberculosis may start within weeks of primary infection. (2)

What It Means to Have a Latent TB Infection

While a person with latent TB has no symptoms and is not infectious, a tuberculin skin test or blood test for TB — called the interferon-gamma release assay, or IGRA — will be positive, showing that the person has not only been exposed to tuberculosis, but has a latent (or “occult”) infection with the bacteria that causes tuberculosis. (2,5)

“You have a ticking bomb waiting for your immune system to get weak,” says Hayan Yacoub, MD, internal medicine practitioner at Austin Regional Clinic in Texas. Latent TB can also complicate treatment for potential health issues that happen later in life, he says. That’s why it’s important to identify and treat latent TB.

If a latent infection is discovered, treatment is recommended in certain individuals at high risk to prevent that person from developing active disease and to prevent the further spread of tuberculosis.

People at high risk of TB infection (such as those who work in hospitals) may be screened, sometimes annually, for latent infection.

Who Should Get Tested for Latent Tuberculosis?

In the United States, there isn’t a need to test everyone for Latent TB because it’s unlikely most people will come in contact with someone who has the active disease.

“The average person doesn’t get exposed to TB,” says Lee Reichman, MD, MPH, professor of medicine and epidemiology and executive director emeritus of the Rutgers Global Tuberculosis Institute in Newark, New Jersey. “For example, if you work in publishing and just go to work and go home, we don’t test you because is unlikely.”

Screening for latent TB is done based on your risk factors. The following populations should be screened: (6,7)

  • People who have recently come to the United States from a country with a high rate of tuberculosis
  • People whose work or living arrangement puts them in contact with people who have active tuberculosis
  • People with other diseases that increase the risk of developing active TB once infected, such as insulin-requiring diabetes, end-stage renal disease, prior gastrectomy, or HIV infection
  • People who are taking drugs that block tumor necrosis factor alpha (TNF-alpha), such as infliximab (Remicade), adalimumab (Humira), or etanercept (Enbrel)

People who plan to start chemotherapy for cancer or an immunosuppressive drug — to treat an autoimmune condition, for example — should also be screened for latent tuberculosis.

The risk of a latent TB infection becoming active is much higher in people infected with HIV than those without HIV, according to an article published in February 2016 in the journal Emerging Microbes & Infections. (8)

What Does Treatment for Latent TB Involve?

Treatment for latent TB involves less medication and a shorter regimen than treatment of active TB, says Alexea M. Gaffney-Adams, MD, an internist and pediatrician with a subspecialty training in infectious disease, at Stony Brook Medicine in Smithtown, New York.

The most commonly used drug for latent TB is isoniazid (Nydrazid), but it needs to be taken for six to nine months in order to kill the bacteria. (5,9)

What It Means to Have Active Tuberculosis Disease

In active tuberculosis, the bacteria multiply in the body, causing noticeable symptoms. This is also when the disease can spread to others. The difference between active and latent TB is the amount of organisms in the body, according to Dr. Reichman.

The most common kind of tuberculosis, pulmonary tuberculosis, typically causes the following symptoms: (5,10)

  • Breathing difficulty
  • Chest pain
  • Coughing, sometimes with phlegm
  • Fatigue
  • Fever
  • Night sweats
  • Weakness
  • Weight loss
  • Wheezing

In addition to the lungs, tuberculosis can affect other parts of the body, including the lymph nodes, other internal organs, bones and joints, or the brain. This form of the disease, called extrapulmonary tuberculosis, also causes fatigue, fever, night sweats, weakness, and weight loss, and may also cause other symptoms depending on what body parts are affected.

Active TB is curable, but the disease can be deadly if left untreated. About 45 percent of people not infected with HIV, and almost all HIV-positive people, will die from TB without proper treatment. (11)

Tuberculosis is spread through the air, which means you can only get it by breathing contaminated air. If someone who is actively sick talks, coughs, sneezes or speaks, they can spread TB. According to the World Health Organization (WHO), people with active TB can infect 10 to 15 other people they come into regular close contact with in the course of a year. (11)

The reality is that if someone does have active TB, they’re breathing bacteria out into the air and anyone can pick them up, says Dr. Gaffney-Adams. “You’re most likely to spread it to your household, but it can definitely spread elsewhere.”

Who Should Get Tested for Active TB Disease?

If you find out you’ve been exposed to someone with TB, you need screening, says Gaffney-Adams. If a first screening was negative, she recommends going in for testing again, especially if you experience any respiratory symptoms.

The CDC recommends screening anyone with the following symptoms for active TB: (7)

  • Coughing that lasts for three weeks or longer
  • Weight loss that can’t be explained
  • Coughing up blood
  • Chest pain
  • Loss of appetite
  • Night sweats
  • Fever
  • Fatigue

According to Gaffney-Adams, who has treated several cases of both latent and active TB, night sweats is a very common symptom in TB. It’s usually pretty dramatic, she says, like sweating so heavily that a person needs to get up and change sheets and clothes.

What Does Treatment for Active TB Involve?

The treatment for any type of active tuberculosis is long-term administration of antibiotics.

Because there are so many drug-resistant strains of TB, people with active disease must take more than one antibiotic to ensure that all of the bacteria are killed. In addition, because tuberculosis bacteria grow slowly, it’s necessary to take the antibiotics for at least six months. (5,12)

Treatment for active TB will include a combination of three to four of these drugs:

  • Isoniazid (Nydrazid)
  • Rifampin (Rifadin)
  • Pyrazinamide
  • Ethambutol (Myambutol)

One major concern in the treatment of active TB is making sure people continue to take the medication even after symptoms have gone away. People typically need to take medication for about a year, so they often get tired of it and forget, says Robert Amler, MD, dean and professor of public health, and professor of pediatrics and environmental health science at New York Medical College in Valhalla, New York.

Stopping the drugs early can cause the TB bacteria to return, and that bacteria may not respond to drugs that worked the first time. This is called drug-resistant TB, and it’s much harder to treat.

To make sure people with active TB finish the full medication schedule, directly observed therapy, or DOT, is used. In DOT, a trained healthcare worker provides each dose of medication, watches the patient swallow it, and documents that the medication has been taken.

Treatment regimens

Isionazid is one of the drugs used to treat latent TB

Since the 1950s many studies have been carried out to assess the effectiveness of the TB drug isoniazid in treating latent TB. In some of the trials the people taking part took the drug for six months, whilst in other trials the drug was taken for twelve months. There were also trials with people taking the drug daily being compared with people taking the drug five times a week.

Any adverse effects of taking the drug were also noted and compared. There was a then long period of follow up to see who developed active TB.2Cruz, Andrea T. “Treatment of Latent Tuberculosis in Children”, Journal of the Pediatric Infectious Diseases Society, 2013,

The initial human studies of isoniazid preventative therapy established that prolonged therapy with isoniazid was effective in reducing subsequent active TB infections. The optimum length of treatment was however unclear but the most common recommendation was for a treatment length of nine months.

Recommended regimens

Currently the American CDC recommends one of the following three regimens for the treatment of latent TB.3“Treatment regimens for latent TB infection”, CDC,

  • Isoniazid daily or twice weekly for nine months
  • Isoniazid plus rifapentine once weekly for 12 weeks
  • Rifampicin (or rifabutin) daily for 4 months (with this regimen dots must be used)

The WHO also recommends two other regimens of 3 or 4 months of isoniazid plus rifampicin daily and six months of isoniazid daily.

Further analysis of trial results

In 2019 the results were reported of a further analysis of 2 clinical trials looking specifically at side effects. An important problem limiting the treatment of latent TB infection is the occurrence of adverse events with isoniazid. As a result of this further analysis it was recommended that in patients without contraindications, rifampicin is likely to be the safest TB infection treatment option.4Adverse events in adults with latent tuberculosis infection, 2019,

Treatment study results in 2018 ACTG 5279

In 2018 the results were announced of the ACTG 5279 study.5R Chaisson, “One month tuberculosis prophylaxis as effective as nine month regimen for people living with HIV”, 2018 Conference on Retroviruses and Opportunistic Infections (CROI) This was a phase 3 clinical study which showed that a one month regimen to prevent latent TB developing into active TB was at least as effective as the current recommended regimens of nine months for people living with HIV. Also, adults and adolescents in the trial were more likely to complete the short course regimen.

The short course regimen consisted of daily doses of the drugs rifapentine and isoniazid.

Among people with latent TB infection, HIV infection is the greatest risk fact for progression from latent TB to active TB disease.

It was said that:

“These results have the potential to dramatically change clinical practice by offering people living with HIV who are at risk of developing active tuberculosis an additional, shorter duration prevention option that is safe, effective and more convenient. This study also will inform future research on prevention of tuberculosis disease among HIV negative people at risk for developing active tuberculosis”NIAID Director Anthony Fauci

Fact Sheet

(PDFCdc-pdf– 213 KB)

Tuberculosis Information for Employers in Non-Healthcare Settings

What is tuberculosis (TB)?

Tuberculosis (TB) is a disease caused by bacteria called Mycobacterium tuberculosis that are spread from person to person through the air. TB usually affects the lungs, but it can also affect other parts of the body, such as the brain, the kidneys, or the spine. Not everyone infected with TB bacteria becomes sick. As a result, two TB-related conditions exist: latent TB infection and TB disease.

What is latent TB infection?

Persons with latent TB infection (LTBI) do not feel sick and do not have any symptoms, but usually have a positive reaction to the tuberculin skin test or TB blood test. They are infected with TB bacteria, but do not have TB disease. Persons with LTBI are not infectious and cannot spread TB infection to others.

What is TB disease?

In some people, TB bacteria overcome the defenses of the immune system and begin to multiply, resulting in the progression from latent TB infection to TB disease. Some people develop TB disease soon after infection, while others never develop TB disease or develop it later in life when their immune system becomes weak. Persons with TB disease usually have symptoms, are considered infectious, and may spread TB bacteria to others.

A person with latent TB infection & A person with TB disease

A person with latent TB infection (LTBI) A person with TB disease
• Usually has a TB skin test or blood test result indicating TB infection • Usually has a TB skin test or blood test result indicating TB infection
• Has a normal chest x-ray and a negative sputum test • May have an abnormal chest x-ray, or positive sputum smear or culture
• Has TB bacteria in his/her body that are alive, but inactive • Has active TB bacteria in his/her body
• Does not feel sick • Usually feels sick and may have symptoms such as coughing, fever, and weight loss
• Cannot spread TB bacteria to others • May spread TB bacteria to others
• Needs treatment for latent TB infection to prevent TB disease • Needs treatment for TB disease

How is TB spread?

TB bacteria are released into the air when a person with TB disease of the lungs or throat coughs, sneezes, speaks, or sings. These bacteria can stay in the air for several hours, depending on the environment. Persons who breathe in the air containing these TB bacteria can become infected; this is called latent TB infection. A person with latent TB infection cannot spread TB to others.

Persons with TB disease are most likely to spread the bacteria to other people they spend time with every day, such as family members or coworkers. Anyone who has been around someone who has TB disease should go to the doctor or local health department for TB tests.

TB is not spread through eating utensils, countertops, chairs, doorknobs, or other surfaces where a TB patient has been.

The general symptoms of TB disease include feelings of sickness or weakness, weight loss, fever, and night sweats. The symptoms of TB disease of the lungs may also include coughing, chest pain, and the coughing up of blood. Symptoms of TB disease in other parts of the body depend on the area affected.

What should I do if an employee reports having a positive TB test or that he or she has been in contact with someone who has TB?

It is important to remember that only a person with TB disease can transmit TB bacteria to others. If an individual has been around someone with TB disease, he or she can get TB infection. However, not everyone infected with TB germs becomes sick. A person with latent TB infection cannot spread germs to other people, but can develop TB disease in the future.

For additional information, contact your local or state TB control program.They can advise you about what should be done.

What will happen after I contact my local or state TB control program for assistance?

The TB control program will determine if the employee has latent TB infection or TB disease. Since people with latent TB infection cannot spread TB to others, nothing further will need to be done in the workplace. However, if the employee has TB disease, the TB control program may start a contact investigation. The investigation will help them find out how the employee may have been exposed to TB and to determine who else might be at risk.

During the investigation, the health department will ask the employee about his or her job, such as the work hours, working conditions, and people who work closely with him or her. The TB control program may set up an appointment to talk with you and to tour your workplace. They may also want to talk to people who regularly visit your workplace. Throughout the investigation, they will work with you to make sure that the employee’s identity is kept confidential.

Additional Information

CDC. Questions and Answers About TB.

CDC. Tuberculosis: General Information.

CDC. The Difference Between Latent TB Infection and Active TB Disease.

CDC. Interferon-Gamma Release Assays (IGRAs) – Blood Test for TB Infection.

CDC. Tuberculin Skin Testing.

CDC. Protect Your Family and Friends from TB: The TB Contact InvestigationCdc-pdf. (PDF)

CDC. TB Control Programs

New technique may quickly distinguish between active and latent TB

“Current blood tests for tuberculosis are reasonably good at distinguishing between uninfected and infected persons, but cannot tell the whether an infected person has active, and possibly infectious, tuberculosis or has latent infection,” said senior author Jason Stout, M.D., M.H.S., assistant professor of medicine at Duke University Medical Center. “Generally a culture is required to tell the difference between latent infection and active tuberculosis, but a culture usually requires weeks to deliver a result. A rapid test that could tell the difference between latent and active tuberculosis would be a major step forward.”

The findings were reported at the ATS 2010 International Conference in New Orleans.

“This pilot study explored whether using patterns in the immune response to tuberculosis could be helpful in improving rapid diagnosis of the disease,” Dr. Stout said.

Dr. Stout and colleagues collected whole blood samples from 71 people belonging to one of three groups: those with active tuberculosis, those with latent tuberculosis infection, and those who were not infected with tuberculosis. After exposing the samples to pieces of the tuberculosis bacteria to stimulate an immune response, researchers measured the levels of 25 specific proteins, called cytokines, to determine the presence of a pattern that could allow them to differentiate among the three groups.

“We found that a pattern of two cytokines, called MCP-1 and IL-15, was reasonably good at differentiating between persons sick with TB and persons infected but not sick,” Stout said. “In addition, a third cytokine, called IP-10, looked promising in distinguishing between uninfected persons and infected individuals.”

Stout said that while previous studies identified all three cytokines as possible individual predictors of tuberculosis infection, the usefulness of the combination of MCP-1 and IL-15 was unexpected.

“These findings could lead to earlier diagnosis of active tuberculosis, which could be beneficial for both the sick person and others around her or him who might be spared from infection,” Dr. Stout noted. “There is also the potential for avoiding unnecessary and potentially toxic medications in persons who are not sick with tuberculosis.”

Although the initial results were promising, Dr. Stout noted the sampling for this pilot study was limited, and added that further research would be needed to determine if the results could be replicated in a larger population, “ideally a group of persons suspected of having tuberculosis.”

“Future studies may also help researchers determine whether examining additional cytokines would improve on the accuracy of our results,” he added.

Deciding When to Treat Latent TB Infection

People with latent TB infection do not have symptoms, and they cannot spread TB bacteria to others. However, if latent TB bacteria become active in the body and multiply, the person will go from having latent TB infection to being sick with TB disease. For this reason, people with latent TB infection should be treated to prevent them from developing TB disease.

Treatment of latent TB infection is essential to controlling TB in the United States because it substantially reduces the risk that latent TB infection will progress to TB disease. In the United States, up to 13 million people may have latent TB infection. Without treatment, on average 1 in 10 people with latent TB infection will get sick with TB disease in the future. The risk is higher for people with HIV, diabetes, or other conditions that affect the immune system. More than 80% of people who get sick with TB disease in the United States each year get sick from untreated latent TB infection.

Treatment of latent TB infection should start after excluding the possibility of TB disease.

Groups Who Should be Given High Priority for Latent TB Infection Treatment include:

  • People with a positive TB blood test (interferon-gamma release assay or IGRA).
  • People with a tuberculin skin test (TST) reaction of 5 or more millimeters who are:
    • HIV-infected persons.
    • Recent contacts to a patient with active TB disease.
    • Persons with fibrotic changes on chest radiograph consistent with old TB.
    • Organ transplant recipients.
    • Persons who are immunosuppressed for other reasons (e.g., taking the equivalent of >15 mg/day of prednisone for 1 month or longer, taking TNF-α antagonists).

  • People with a TST reaction of 10 or more millimeters who are:
    • From countries where TB is common, including Mexico, the Philippines, Vietnam, India, China, Haiti, and Guatemala, or other countries with high rates of TB. (Of note, people born in Canada, Australia, New Zealand, or Western and Northern European countries are not considered at high risk for TB infection, unless they spent time in a country with a high rate of TB.)
    • Injection drug users.
    • Residents and employees of high-risk congregate settings (e.g., correctional facilities, nursing homes, homeless shelters, hospitals, and other health care facilities).
    • Mycobacteriology laboratory personnel.
    • Children under 4 years of age, or children and adolescents exposed to adults in high-risk categories.

Persons with no known risk factors for TB may be considered for treatment of LTBI if they have either a positive IGRA result or if their reaction to the TST is 15 mm or larger. However, targeted TB testing programs should only be conducted among high-risk groups. All testing activities should be accompanied by a plan for follow-up care for persons with latent TB infection or disease.

As of 2018, there are four CDC-recommended treatment regimens for latent TB infection that use isoniazid (INH), rifapentine (RPT), and/or rifampin (RIF). All the regimens are effective. Healthcare providers should prescribe the more convenient shorter regimens, when possible. Patients are more likely to complete shorter treatment regimens. Treatment must be modified if the patient is a contact of an individual with drug-resistant TB disease. Consultation with a TB expert is advised if the known source of TB infection has drug-resistant TB.

Related Links

  • State TB Control Offices

For Patients

For Health Care Providers

  • Latent Tuberculosis Infection: A Guide for Primary Health Care Providers
  • Treatment Guidelines Update on Recommendations for Use of Once-weekly Isoniazid-Rifapentine Regimen to Treat Latent Mycobacterium tuberculosis Infection
  • The 12-Dose Regimen for Latent TB Infection Treatment: Fact Sheet for CliniciansCdc-pdf
  • Frequently Asked Questions on the 12-Dose Regimen (3HP) for Latent TB Infection Treatment
    • Frequently Asked Questions on the 12-dose regimen for Latent TB Infection for Providers
    • Frequently Asked Questions on the 12-dose regimen for Latent TB Infection for Pharmacists
  • Latent TB Infection Online Resources

Management of latent tuberculosis infection


When people with infectious tuberculosis (TB) cough, sneeze or otherwise exhale droplets, they expose others to Mycobacterium tuberculosis. After a person is exposed, they can be infected with M. tuberculosis without having TB disease and without signs and symptoms. This is called latent TB infection (LTBI).

In people with LTBI, live TB bacilli remain inactive without causing disease, however the bacilli can at some point become active, multiply, and cause TB disease. The risk of progressing from LTBI to active TB disease is related to the virulence of the M. tuberculosis strain and the susceptibility of the host (e.g. malnutrition, immunocompromised status). People with LTBI represent a large human reservoir for TB, which is why management of LTBI is a crucial step towards TB elimination.

Around 60 000 cases of TB are reported annually in the European Union/European Economic Area (EU/EEA), with most countries in the region characterised by low-incidence of the disease (fewer than ten tuberculosis cases per 100 000 population). According to a recent estimate published in PLOS Medicine 1.7 billion people globally have LTBI – almost a quarter of the world’s population. In low incidence countries, a majority of TB cases occur due to the progression of LTBI from passive to active disease. This is why it is crucial to improve management of LTBI in Europe.

LTBI Management

To help decrease the incidence of LTBI, a variety of targeted public health measures need to be implemented.

It is crucial to identify groups at risk of contracting LTBI and those within the groups at risk of progressing to active TB. Identification of risk groups will enable targeted screening and treatment. Among the prioritised groups are people living with HIV, immunocompromised persons, patients with silicosis, people with pulmonary fibrotic lesions and contacts of infectious TB cases. Once the target groups are identified, defining a thorough diagnostic approach to detect LTBI is paramount. This approach should always involve screening with the tuberculin skin test and/or interferon gamma release assays. Detection of LTBI should be followed by treatment using a regimen based on an individual risk assessment and regular follow-up to ensure adherence.

Throughout the process, a culturally considerate and patient centred approach should be applied. This could include material incentives, counselling, education and peer-based support. Effective health education and communication should be maintained with target groups and healthcare providers concerning the importance of detecting and treating LTBI. To evaluate the suitability and effectiveness of LTBI management, reporting and monitoring procedures need to be implemented. Reporting systems should have adequate data collection processes, with defined performance indicators. National procedures should preferably be aligned with global and regional monitoring and evaluation frameworks, to enable country comparisons.

ECDC has developed various resources to help EU/EEA countries prevent and control LTBI:

Active TB Disease and Latent TB Infection

A person who is exposed to TB may not necessarily develop the disease. Most people are able to fight the infection using various components of their immune system. In fact, healthy people who are infected with TB only have a 10% chance of converting to active disease over their lifetime. Some are able to control the infection, but unable to completely remove it from their bodies. In these cases, the infection remains, lying in an inactive or “latent” state. This is often described as Latent TB Infection or LTBI. LTBI may develop into active disease someday, often when the persons immune system becomes weakened.

People with latent TB infection do not show any signs of TB disease so it can go unnoticed. Since this latent infection can become active at any time and then spread to other individuals it is usually treated with antibiotics.

People with active TB disease do have signs and symptoms. These symptoms of active TB disease are easy to confuse with those of many other diseases. This chart details the main differences between active TB disease and latent TB infection.

Active TB Disease

Latent TB Infection

Can be spread to others Yes, through droplets in the air No, Mycobacteria are not expelled
Chest x-ray Abnormal findings; will show signs of damage Abnormal findingsrarely seen
Sputum Test (SSM) Test may be positive Test will be negative
Antibiotic treatment Yes, to treat active disease Yes, to prevent conversion to active disease

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