Tuberculosis – Causes, Signs and symptoms


Also called: Mycobacterium Tuberculosis Infection, Tuberculosis Disease, Tubercular Infection, Consumption, TB

Reviewed By:
Vikram Tarugu, M.D., AGA, ACG


Tuberculosis (TB) is a contagious disease caused by the airborne bacterium Myobacterium tuberculosis. It usually affects the lungs, although it can spread to other organs in the body. In many cases, it can be successfully treated with a course of antibiotics. It is a relatively rare disease in the United States, although some groups of people may have an increased risk of contracting TB, including:

  • People with HIV or AIDS
  • People who were born in a country with high TB rates
  • Older adults
  • People who live or work in poverty and are medically underserviced
  • Substance abusers

Not everyone who encounters the TB bacteria will become sick. In most people, the TB bacteria are fought by the immune system and isolated from the rest of the body by special white blood cells. Once TB bacteria have been isolated, they can survive in a dormant state (latent TB) within the body for many years. Latent TB produces no symptoms and people with the dormant bacteria are not contagious. However, if a person’s immune system weakens, the bacteria may become reactivated and multiply in the lungs. When the bacteria are actively causing disease, it is called active TB. Active TB is highly contagious and can produce symptoms such as:

  • Cough that lasts for over three weeks
  • Discolored or bloody sputum (mucus coughed up from the lungs)
  • Night sweats
  • Chills
  • Fatigue
  • Mild fever
  • Loss of appetite that may cause weight loss
  • Pain in the chest while breathing or coughing

It is important that people who suspect they have been infected with TB consult their physician for a skin test. Active TB remains contagious for at least two weeks after medication is started. People diagnosed with active TB should stay at home and limit their contact with others until a physician indicates it is safe to resume contact with others.

TB is often diagnosed using a skin test. If the results are positive, the physician may conduct additional tests to confirm the extent of the infection. Once diagnosed, TB is treated with a combination of different antibiotics taken for between six months and a year. It is very important that people with TB take their medication for the full course. Failure to take the entire course of antibiotics can lead to antibiotic resistance, which makes treatment far more difficult.

Treating TB in patients with HIV can be especially difficult. Many of the medications used to treat TB interfere with the medications used to treat HIV. Also, studies have shown that TB bacteria may hasten the progression of HIV into AIDS.

Unfortunately, there is little that individuals can do to prevent contracting TB if they have close contact with someone who is infected. For this reason, people should avoid contact with people known to have TB and take protective measures if caring for an infected person. People with TB can avoid spreading the disease by practicing good personal hygiene and taking all prescribed medication. There is no effective vaccine available for TB.

About tuberculosis

Tuberculosis (TB) is a contagious disease that usually affects the lungs, but can also spread to other parts of the body. It is caused by the airborne bacterium Myobacterium tuberculosis. Because it is airborne, TB is generally transmitted when someone infected with TB coughs, sneezes, laughs or otherwise expels breath into the air. Once in the air, the bacteria can stay alive for several hours. However, brief exposure to TB bacteria rarely results in infection. Most people who contract TB become infected after repeated exposure to the bacteria (e.g., from another household member).

In most cases, an infection causes no symptoms and the bacteria remain dormant in the body for many years. A person in this state is said to have latent TB. Latent TB occurs when the TB bacteria enter the body, but are attacked by a healthy immune system and neutralized when the bacteria reach the lungs. This usually happens within two to eight weeks of exposure to the bacteria. The bacteria remain alive in the body, but surrounded by a wall of white blood cells called macrophages, which create scab-like seals around the bacteria.

Latent TB produces no symptoms, is not contagious and, in 90 percent of cases, causes no problems for the infected person, according to the American Lung Association (ALA). However, latent TB can later reactivate if the immune system becomes compromised. When this happens, the macrophages begin to fail and the TB bacteria become active and begin to multiply.

Active TB (its disease state) produces symptoms and is highly contagious. When latent TB becomes reactivated, the TB bacteria form cavities in the lungs (pulmonary TB), where they continue to multiply and sometimes spread through the blood to other parts of the body, such as the kidneys, lymph nodes, reproductive system and the tissue surrounding the brain (extrapulmonary TB).

Roughly 10 percent of people with latent TB develop active TB, according to the ALA. Active TB is most likely to develop within the first year of infection by TB bacteria. This can happen for a variety of reasons, such as contracting a common illness (e.g., influenza or the common cold), taking certain medications or getting older, all of which may weaken the immune system. 

TB occurs most often among:

  • Patients with HIV/AIDS or other illnesses that affect the immune system
  • People born in a country with high TB rates
  • Older adults
  • People living in poor areas and who are medically underserviced
  • Substance abusers

Cases of TB in children represent a small percentage of overall TB cases. Children usually contract TB from adults who have the disease. Additionally, there is a small risk that women with TB who are pregnant may pass the disease to their child. More commonly, babies born to infected mothers may be underweight and have other health problems. Because of this, pregnant women are often treated for latent TB. Although there is evidence that the antibiotics used to treat TB in pregnant women may cross the placenta, this does not seem to harm the fetus.

In the 1800s, many deaths worldwide were caused by TB. Since the 1940s, medical advancements have significantly reduced the prevalence of the disease in the United States and other developed countries. In the 1980s and early 1990s, there was a resurgence of TB cases in the United States. This was due in part to the AIDS epidemic, increased immigration from countries with high TB rates and higher instances of poverty and drug use, all of which are major risk factors for TB.

By the middle of the 1990s, national efforts to control the spread of TB resulted in a considerable drop in the number of reported cases, although the rate of decline has slowed in recent years. According to the U.S. Centers for Disease Control and Prevention (CDC), 10 million to 15 million people in the United States have latent TB, and over 14,000 cases of active TB were reported in 2005. In many countries, tuberculosis is a serious health risk for many people. According to the World Health Organization (WHO), 8 million people develop active TB throughout the world and almost 2 million people die as a result of the disease every year.

Risk factors and causes of tuberculosis

Infection with tuberculosis (TB) usually occurs when airborne droplets containing the bacterium Myobacterium tuberculosis are inhaled. These droplets may be present when someone infected with TB coughs, sneezes, laughs or otherwise expels breath into the air. Once in the air, the bacteria can stay alive for several hours. Brief exposure to these bacteria rarely results in infection. Most people who contract TB become infected after repeated exposure to the bacteria (e.g., from another household member).

Anyone can become infected with TB. Because TB is caused by close contact with people who are already infected with TB, anyone who lives or works closely with someone with TB is at risk. However, the risk of contracting TB from contact with infected people is significantly increased among certain groups.

The most significant risk factor for TB is a weakened immune system. It is because of this that people with the human immunodeficiency virus (HIV) or acquired immunodeficiency syndrome (AIDS) are most at risk for TB. Both AIDS and the virus that causes it, HIV, damage the body’s immune system. This damage makes people with HIV or AIDS less able to fight infections, including TB.

People with HIV or AIDS are also more likely to experience complications. People with HIV are also more likely to develop TB in organs apart from the lungs (extrapulmonary TB). In addition, medications used to treat TB can interfere with those used to treat HIV and AIDS, making it difficult to effectively treat HIV/AIDS and TB. On a global scale, people with HIV are more likely to die from TB than any other disease. This is not the case in the United States, where TB is less prevalent.

However, TB is still a serious threat to people with HIV in the United States. According to the U.S. Centers for Disease Control and Prevention (CDC), 10 percent to 15 percent of all TB cases in the United States occur in people with HIV. Therefore, people who are diagnosed with TB are also advised to undergo testing for HIV.

Other factors which may increase a person’s risk of contracting TB, such as by adversely affecting the immune system, include:

  • Autoimmune disorders such as diabetes and thyroid disease. Autoimmune disorders occur when the body attacks and damages its own tissue, mistaking the tissue as a threat. These conditions can suppress immunity, making it harder to fight a TB infection.
  • Malnutrition. Failure to consume enough calories or maintain a balanced diet can impair the immune system. This is a particular risk for people who live in poverty.
  • Substance abuse. The immune systems of people who are long-term abusers of illegal drugs or alcohol are often weakened due to long-term exposure to these substances, making them vulnerable to TB infection. Also, some TB medications can cause complications for those receiving methadone (a drug used to treat heroin addiction).
  • Age. As the body ages, the immune system weakens. Additionally, older people are more likely to have been exposed to TB bacteria when young and have latent TB (dormant TB bacteria in the body), which may reactivate as the immune system weakens.
  • Smoking. Recent studies have shown that smokers have an increased risk of developing both latent and active tuberculosis. According to these studies, a person who smokes may be as much as twice as likely to develop active tuberculosis than a non-smoker.

Another important risk factor for TB is a person’s country of birth. People who were born in a country that has a high incidence of TB such as some countries in Africa, Asia and Latin America account for over half the cases of TB in the United States, according to the CDC. People from these countries also have a higher rate of multidrug-resistant TB (MDR TB), a deadly strain of TB that is resistant to two or more of the most common TB medications, and extreme drug-resistant TB (XDR TB), a strain of TB that is resistant to most TB medications. This is largely because countries with high TB rates also tend to have poor health care and a lack of consistent treatment available for people with TB. Thus, the bacteria to which people from these areas of the world are exposed are more likely to be antibiotic-resistant.

People living or working in crowded conditions (e.g., in prisons, nursing homes, homeless shelters) also have an increased risk of TB. TB can easily spread in poorly ventilated areas where people spend large amounts of time together. Poverty increases the risk of living in a crowded environment. It also means these people would not be likely to receive adequate medical care.   It is advised that anyone at risk of TB, including children, be periodically tested for the disease.

Signs and symptoms of tuberculosis

In most cases, tuberculosis (TB) produces no symptoms and causes no immediate harm to the body. People with healthy immune systems are able to fight and disable the bacteria that can cause TB. These disabled bacteria may remain dormant in the body (latent TB) for many years, although they can be reactivated (active TB) when the immune system weakens.

Signs and symptoms of an active TB infection include:

  • A cough that lasts for over three weeks
  • Discolored or bloody sputum (mucus coughed up from the lungs)
  • Night sweats
  • Chills
  • Fatigue
  • Mild fever
  • Loss of appetite, which may cause weight loss
  • Pain in the chest while breathing or coughing

TB can spread to other parts of the body (extrapulmonary TB), in which case different symptoms may occur, including:

  • Painful urination or blood in the urine – TB in kidney or bladder
  • Pus draining from lymph nodes – TB in lymph nodes
  • Lump in scrotum (in men) or sterility (in women) – TB in reproductive system
  • Back pain or paralysis – TB in spine

Because the symptoms of TB gradually appear over a long period of time, TB can often be mistaken for a bad cold or case of the flu. It is important that people who experience symptoms of TB immediately consult their physician at the onset of symptoms. TB can be highly contagious and must be treated as soon as possible.

Diagnosis methods for tuberculosis

A physician may suspect that a patient is suffering from tuberculosis (TB) based on reported symptoms and the patient’s risk of contracting TB. The physician may also compile a medical history and perform a physical examination. If TB is suspected, a number of additional tests may also be conducted.

The most common test for TB is the Mantoux tuberculin skin test (or TST). This test is safe for use in infants, children, pregnant women and people with compromised immune systems (including patients with HIV). However, it is not recommended for people who have had an allergic reaction to previous TSTs. A TST is sometimes carried out as a routine screening test for children and adults at risk of contracting TB.

During the TST, a small quantity of fluid called tuberculin is injected just under the skin on the inside of the forearm. Within 48 to 72 hours, the patient must return to the physician, who will inspect the site of the injection for a raised lump or welt. For people who have no known risk factors, the test is considered positive for TB if the patient displays a lump of over 15 millimeters (mm) in diameter. For those in high-risk groups, a 5-mm lump could indicate infection. If there is no lump, the test is considered negative.

The TST is only capable of indicating the presence of TB bacteria. It does not differentiate whether the infection is latent (when bacteria are dormant in the body) or active (bacteria are actively causing disease).

Also, the TST may sometimes produce results that are false-positive (results incorrectly indicate TB although TB bacteria are not present) or false-negative (results incorrectly indicate absence of TB even though TB bacteria are present).

A false-positive reaction could be due to several factors, including:

  • Latent TB. A false-positive result may indicate the presence of dormant TB bacteria in the body. These bacteria are not active and not currently causing symptoms of disease.
  • Infection with bacteria that are similar to the bacterium that causes TB (Myobacterium tuberculosis).
  • Previous vaccination to TB with the live vaccine, Bacille Calmette-Guerin (BCG).
  • Incorrect administration of the TST (e.g. fluid injected too deep under the skin).
  • Inaccurate reading of the TST.

A false-negative reaction is more common and can be due to the following factors:

  • Recent TB infection. It can take up to eight or 10 weeks after exposure to the TB bacteria for the body to react to a skin test such as a TST. Generally, symptoms of TB appear (typically within two to eight weeks after exposure to TB bacteria) before the bacteria can begin to be identified by the TST.
  • Impaired immune function. In some cases, the immune system may be too weak to mount a defense against the TST to produce a reaction. This may occur if the patient is suffering from an illness such as HIV or is taking medication that weakens the immune system. This can also happen if the body is overwhelmed with TB bacteria. Some people with impaired immune systems may be unable to react to skin tests such as the TST (a condition called cutaneous anergy).
  • Young age. Children under 6 months old often do not react to skin tests.
  • Recent vaccination with a live virus. Live-virus vaccinations such as those administered to prevent measles or smallpox may produce a false-negative TST reaction. People are advised to wait four to six weeks after a live-virus vaccination before they undergo a TST.
  • Incorrect administration or reading of the TST.

If the TST results are positive, or if a physician suspects that results are a false-negative, additional tests may be performed to confirm the presence of active TB. In these cases, a physician may recommend a chest x-ray to look for signs of TB in the lungs. In people with latent TB, a chest x-ray may show the small, scab-like areas (macrophages) where white blood cells have walled off TB bacteria. In people with active TB, a chest x-ray may show cavities that have formed after the infection broke out of the macrophages.

A physician may also perform a culture, which involves sending samples of sputum (mucus coughed up from the lungs) to a laboratory, where they are tested for signs of TB bacteria. Cultures are also used to assess what TB medications may most effectively kill the bacteria. This can help a physician develop a specific antibiotic treatment plan for a patient.

People with HIV are more likely to develop TB in additional organs of the body and thus may be tested for evidence of TB bacteria in organs such as the brain, spine, kidneys or lymph nodes.

Other tests that may be used to diagnose TB include the tine test, where a small amount of the tuberculosis antigen is injected under the skin in the arm. It is administered with a multi-pronged instrument that contains the antigen on each of the tines (spokes) that penetrate the skin. Like the TST, this test produces a small, raised bump if the body has been exposed to TB bacteria. In addition, other blood tests can also be used to diagnose the presence of TB bacteria in the body. However, the TST is considered the most accurate and is the preferred method of diagnosing TB in the United States. Researchers are investigating new methods to diagnose TB that may be more accurate than the TST. 

It is advised that anyone at risk of TB, including children, be periodically tested for the disease.

Because of their increased risk, people with HIV should be tested for TB on a yearly basis. They should also get tested under the following circumstances:

  • When first diagnosed with HIV
  • When starting HIV therapy
  • After coming into contact with someone with active TB
  • When experiencing any symptoms which could indicate TB

Physicians are required by law to report all confirmed cases of TB to state or local health agencies within 24 hours in order to prevent an outbreak of the disease.

Treatment options for tuberculosis

The most effective treatment for tuberculosis (TB) is a course of antibiotics. This applies to current, symptomatic TB infections (active TB) as well as asymptomatic infections in which dormant TB bacteria are present in the body (latent TB). As long as the entire course of antibiotics are taken, and the bacterial strain is not antibiotic-resistant, antibiotics almost always cure TB.

Some of the antibiotics prescribed for TB have a number of side effects. Some types can turn the color of a person’s saliva, urine or tears orange. Other types may interfere with additional medications patients may be taking. Some of the more severe side effects of TB antibiotics may include nausea, vomiting, jaundice (yellowing of skin or eyes), rash, vision or hearing problems, tingling in the fingers or toes, and fever. Patients who experience any of these symptoms while taking medications to treat TB should immediately consult their physician.

Usually, patients with TB are initially prescribed several different types of antibiotics to ensure that all the TB bacteria are killed. Some of these antibiotic combinations may be available in a single-pill form. After a certain length of time, the number of different medications necessary may be reduced. TB bacteria are slow to respond to treatment. Thus, antibiotics must be taken regularly (usually every day) for between six months and a year. Additionally, women who are pregnant and being treated for TB may need to take vitamin B6 supplements.

After two or three weeks of treatment, the symptoms of TB begin to disappear and the disease is no longer contagious. However, despite a lack of symptoms, it is vital that TB patients continue to take the entire course of their medications. If antibiotics are stopped before all the bacteria are killed, the remaining bacteria may grow resistant to the antibiotics that were used. This can result in the development of multidrug-resistant TB (MDR TB) that are more deadly and harder to treat.

Because of the importance of continuous treatment, many health departments offer a program called directly observed therapy (DOT). With DOT treatment, a patient meets with a healthcare worker every day or several times a week to take the TB medication. The healthcare worker can observe that the medication has been administered and also answer any questions the patient may have about treatment. If a patient does not participate in DOT, it is still important to maintain contact with a physician on a regular basis to ensure that treatment is progressing.

Patients with HIV who receive effective treatment are likely to completely recover from TB. However, developing a treatment plan that is effective can be a difficult task. People with HIV are at a significantly higher risk of being infected with MDR TB. These antibiotic-resistant bacteria are often immune to the effects of the medications usually prescribed to treat TB.

People with MDR TB may be forced to use second-line antibiotics, many of which may have serious side effects. Additionally, some of the common TB antibiotics (both first- and second-line types) can adversely interact with medications used to treat HIV (e.g., antiretroviral agents). It is important that patients with both HIV and TB consult a physician who is a specialist in both diseases in order to explore all possible treatment options. If suitable medications are not found, TB may be fatal within months of its diagnosis in these patients. In addition, studies have shown that TB bacteria may accelerate the progression of HIV towards AIDS.

In rare cases, surgery may be necessary to remove part of the lung or other organs that have been damaged by the TB bacteria.

If active TB is left untreated, it is more likely to spread to other parts of the body and can cause permanent damage and death. If latent TB is left untreated, it can reactivate later in life when the immune system becomes weak. This causes the patient to experience symptoms of an active infection, and creates the possibility that the patient can spread TB to others.

Antibiotic resistance and tuberculosis

In recent years, new strains of tuberculosis (TB) bacteria have developed antibiotic resistance to one or more of the primary medications typically used to treat the disease. The disease caused by these antibiotic-resistant bacteria is called multidrug-resistant tuberculosis (MDR TB).

The main cause of MDR TB is partial or inconsistent antibiotic treatment. Because treatment of TB may involve taking medications for several months to a year after symptoms have disappeared, it is easy for people to forget or decide to no longer take their medications. Also, people who do not have the money for or access to adequate health care may only receive short-term or sporadic treatment. This allows the TB bacteria to become resistant to the medication used to treat it.

A patient with MDR TB can transmit the disease in its antibiotic-resistant form, potentially creating new cases of MDR TB that will also be difficult to treat.

Hospitalized patients have an increased risk of contracting MDR TB secondary to the condition for which they were hospitalized (a nosocomial infection). This is because many patients who are hospitalized have weakened immune systems, making them more susceptible to infection. In addition, many of the strains of TB bacteria common in hospitals (and to which patients may be exposed) are already antibiotic-resistant.

MDR TB is difficult to successfully treat. It may not be recognized until months after a patient has started taking the initially prescribed antibiotics, wasting valuable treatment time. People with MDR TB are usually prescribed a longer course of treatment – often up to two years – and treatment may include second-line drugs. These second-line drugs are not suitable for everyone (e.g. children, pregnant women) because of their serious side effects. MDR TB is especially dangerous for patients with HIV or AIDS, for whom TB is often fatal within months of diagnosis.

Recently, a more deadly strain of TB, called extreme drug-resistant TB (XDR TB), has emerged. XDR TB is resistant to at least three, and sometimes up to six, of the antibiotics commonly used to treat TB, making it virtually impossible to treat. According to the World Health Organization (WHO), 4 percent of MDR TB cases in the United States are actually misdiagnosed cases of XDR TB. In some countries, especially those in the former Soviet Union and Africa, almost 20 percent of MDR TB cases are really XDR TB. 

Despite the fact that the overall rate of TB in the United States has steadily declined over the last 10 years, cases of MDR TB are increasing. According to the U.S. Centers for Disease Control and Prevention (CDC), the number of MDR TB cases increased by more than 13 percent in 2004. It is thought that many cases of MDR TB may turn out to be XDR TB.

Prevention methods for tuberculosis

There are several ways people can protect themselves against infection by tuberculosis (TB) bacteria. Most importantly, people should avoid contact with people known to be infected with TB. Healthcare workers or anyone caring for people infected with TB should wear protective masks while interacting with the infected person.

Anyone at risk of contracting TB should be regularly tested for the presence of TB bacteria. This may facilitate early treatment and cure of the disease, and help prevent its spread to others. High-risk populations that should be regularly tested include:

  • Patients with HIV or AIDS
  • Anyone with medical conditions or on medications that impair their immune system
  • Older adults
  • People born in countries with high rates of TB
  • Substance abusers

Public health authorities can help lower TB rates in communities by regularly testing people in high-risk groups and offering treatment for people with latent TB (when dormant TB bacteria are present in the body). This may be especially helpful for people who live or work in poverty or who are otherwise not able to access appropriate medical care.

There is currently no effective vaccine against TB that is available in the United States. Some countries, especially those that have high rates of TB infection, use a vaccine for TB called Bacille Calmette-Guerin (BCG). This vaccine is not commonly used in the United States because of the low prevalence of TB and the fact that it does not guarantee protection against TB in adults. Additionally, the BCG vaccine uses a live version of TB bacteria that interferes with testing results and has been known to cause disease in people with impaired immune systems.

However, the BCG vaccine may be recommended for certain groups, such as healthcare workers who interact with TB patients, and children who live with infected adults. Scientists are currently developing a vaccine for TB that may be used in people at high risk of contracting TB, such as patients with autoimmune disorders.

People who have been diagnosed with active TB (the disease-causing infection) can prevent its spread by taking the following measures:

  • Staying indoors in a well-ventilated room and reducing contact with other people while contagious.
  • Covering the mouth and nose with a tissue when coughing or sneezing and then immediately disposing of the tissue.
  • Taking the entire course of all prescribed medications, as recommended by the patient’s physician.

Active TB remains contagious for at least two weeks after TB medication is started. People diagnosed with active TB should limit their contact with others until a physician indicates it is safe to resume contact. People with latent TB may be encouraged to take a long-term dose of antibiotics to kill the dormant bacteria in their bodies. This can prevent the development of an active TB infection later in life. This is particularly important for patients with impaired immune systems.

Questions for your doctor about tuberculosis

Preparing questions in advance can help patients to have more meaningful discussions with their physician regarding their conditions. Patients may wish to ask their doctor the following questions related to tuberculosis (TB):

  1. Do my symptoms indicate TB?
  2. How can I find out if I have a latent (dormant) or active TB infection?
  3. Under what conditions will a latent infection turn into an active one?
  4. How will TB affect my pregnancy?
  5. Am I contagious? How can I prevent spreading infection to other members of my household?
  6. What type of treatment will I need? What side effects are possible? Will this treatment interfere with any of my current medical conditions or medications?
  7. For how long will I have to take these medications? What should I do if I miss a dose?
  8. What should I do if my symptoms return during treatment?
  9. After treatment, is my TB likely to return?
  10. How can a TB infection be prevented?
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