Tuberculosis, or TB, is an infectious disease caused by the bacterium Mycobacterium tuberculosis.
The bacterium is spread through the air when someone with the disease coughs, sneezes, or speaks.
TB generally doesnt cause symptoms immediately. Instead, it goes through three stages:
In most people, TB is latent, meaning the bacteria are present in the body but are in a dormant state, neither making the person sick nor infecting others.
Tuberculosis is more likely to enter the active phase in people who have acquired the infection recently (in the past two years) and among those whose immune systems are weakened as a result of malnutrition, old age, infection with HIV, taking immunosuppressant drugs, or among patients who are on dialysis.
While there are effective treatments for tuberculosis, the disease can be fatal: According to the Centers for Disease Control and Prevention (CDC), tuberculosis kills more than a million people every year worldwide.
As recently as the 1800s, TB (formerly known as "consumption" or "phthisis") caused more deaths in industrialized countries than any other disease.
The development in the 1940s of streptomycin, the first antibiotic to effectively cure TB, dramatically lowered the number of cases of tuberculosis seen in developed countries, including the United States.
Today, most cases of TB occur in Africa, Asia, and the Western Pacific region.
CDC statistics for TB show the following for 2013:
When active tuberculosis is diagnosed in the United States, its often in a person who has emigrated from a country with a much higher rate of TB.
The most common symptom of TB is a persistent cough that produces yellow or green sputum, particularly first thing in the morning.
As the disease progresses, the sputum may become streaked with blood.
Some other symptoms of tuberculosis include:
Tuberculosis is treated with antibiotics. The most commonly used are isoniazid (Nydrazid), rifampin (Rifadin), pyrazinamide, ethambutol (Myambutol), and occasionally streptomycin.
However, many strains of tuberculosis have become resistant to these antibiotics, largely because of improper use of them or inadequate treatment.
Antituberculosis antibiotics must be taken for a long time usually 6 months or longer because the tuberculosis bacteria are very slow-growing. When antibiotics are stopped too early, before all of the bacteria in the body have been killed, those bacteria that remain often become resistant to the drug(s) that were being used.
The emergence of multidrug-resistant tuberculosis has become a major threat to successfully controlling the spread of TB worldwide.
Consequently, people diagnosed with TB today must take multiple antibiotics at once to make sure all of the bacteria are killed.
A vaccine for tuberculosis called bacille Calmette-Guerin, or BCG, is used in parts of the world with high rates of the infection to prevent serious complications such as meningitis.
BCG is rarely used in the United States, however, because some studies have shown that BCG is not very effective in preventing TB cases, and because treatment of latent TB infection with isoniazid is a more effective strategy to prevent tuberculosis.
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Tuberculosis is unlike most bacterial infections in that it usually doesnt cause symptoms immediately.
Most commonly, tuberculosis (TB) goes through three stages:
Infection with Mycobacterium 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 engulfed 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.
However, 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.
In latent tuberculosis, the bacteria are dormant. A person has no symptoms and is not infectious.
However, 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 latent (or occult) infection with the bacteria that causes tuberculosis.
Treatment of latent infection, if discovered, 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.
People who plan to start chemotherapy for cancer or an immunosuppressive drug to treat an autoimmune condition, for example may also be screened for latent tuberculosis.
In people without HIV infection, the risk of latent infection becoming active disease has been estimated at 10 percent over a lifetime. But for people infected with HIV, the risk increases significantly.
In active tuberculosis, the bacteria multiply in the body, causing symptoms and physical changes.
The most common kind of tuberculosis, pulmonary tuberculosis, typically causes the following symptoms:
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.
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, its necessary to take the antibiotics for at least 6 months. Stopping the drugs early can result in a recurrence of TB that may not respond to the drugs that worked the first time.
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The bacteria that cause tuberculosis (TB) multiply very slowly, so the symptoms of the disease also develop slowly, usually over months to years.
And because many of the symptoms are vague and can have other causes, they are often not recognized as early symptoms of tuberculosis.
The classic symptoms of active tuberculosis are a general sense of being unwell, loss of weight and appetite, night sweats, intermittent fever, generalized body aches, and fatigue.
Tuberculosis most commonly affects the lungs, a condition called pulmonary tuberculosis. When it affects parts of the body besides the lungs, it is called extrapulmonary tuberculosis.
Pulmonary tuberculosis typically causes a persistent cough that may produce yellow or green sputum first thing in the morning. Over time, the sputum may be streaked with blood, although large amounts of blood are unusual.
The cough is often blamed on smoking, asthma, or a recent illness, rather than being recognized as a symptom of TB.
Pulmonary tuberculosis can also cause night sweats, in which a person wakes up drenched in sweat. It may or may not cause a fever.
As the infection progresses, people feel tired and generally unwell. They may lose weight because of a loss of appetite.
Two other common symptoms of pulmonary tuberculosis are chest pain and shortness of breath.
These symptoms may result from pleural effusion an accumulation of fluid between the thin membranes (the pleura) that cover the lungs and line the inside of the chest wall. Or they can be a sign of a pneumothorax, the presence of air between the pleura.
Extrapulmonary tuberculosis may result from pulmonary TB that has spread via the bloodstream. It causes a variety of symptoms, depending on where the active disease is located:
Extrapulmonary tuberculosis can be difficult to diagnose and is often mistaken for another condition or illness initially.
Miliary tuberculosis, or disseminated tuberculosis, is a potentially life-threatening form of TB in which large numbers of tuberculosis bacteria spread throughout the body via the bloodstream.
Its more common in people with a weakened immune system.
The symptoms of miliary TB are the same as those seen in other types fatigue, weight loss, fever, chills, weakness, and difficulty breathing making it difficult to diagnose.
Late in the disease, a chest x-ray of miliary TB shows millions of tiny spots throughout the lungs.
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Tuberculosis is caused by the airborne bacteria Mycobacterium tuberculosis.
It can also be caused by Mycobacterium bovis, which lives in animals and can be transmitted to children who drink unpasteurized milk from infected cows.
In developed countries, however, cattle are tested for tuberculosis, and most milk is pasteurized.
Mycobacterium tuberculosis is spread from person to person when someone with an active form of the disease emits tiny, bacteria-containing droplets into the air through coughing, sneezing, talking, singing, or laughing.
The bacteria can remain suspended in the air for hours, potentially infecting anyone who breathes them in.
Not everyone who inhales TB bacteria gets sick, however. Some peoples immune systems immediately kill the bacteria. In others, the bacteria remain in a latent, or dormant, state.
Developing active tuberculosis is much more likely if a person has a weakened immune system because of HIV or another reason. In addition, the rate of developing active tuberculosis is highest in the two years after initial infection (i.e., among those with a recently acquired infection).
Risk factors for tuberculosis include anything that weakens a persons immune system or puts someone in frequent, close contact with people who have active TB.
In the United States, some of the main risk factors for tuberculosis include:
To prevent the transmission of tuberculosis in healthcare settings, the Centers for Disease Control and Prevention (CDC) has issued guidelines that require most employees to be screened for tuberculosis upon being hired and subsequently on a regular, often annual, basis.
Some residential institutions, such as nursing homes, also screen all new residents for tuberculosis. Screening for active TB is best accomplished by a chest X-ray.
Some other steps toward preventing the spread of TB include:
In DOT, a trained healthcare worker provides each dose of medication, watches the patient swallow it, and documents that the medication has been taken.
Studies show a higher cure rate among people receiving DOT than among those self-administering their TB drugs.
While anyone with tuberculosis is a candidate for DOT, the CDC specifically recommends that patients in the following groups receive it:
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Slowing the spread of tuberculosis requires catching it early and treating it early.
If tuberculosis (TB) can be caught in the latent stage, it can be treated before that person develops active disease and becomes infectious.
In the United States, screening for latent tuberculosis is done in the following populations:
Three tests are used to screen for tuberculosis: chest x-ray (best used to screen for active TB), the tuberculin skin test, and the interferon gamma release assay (IGRA) blood test. The latter two tests are approved in the United States for the diagnosis of latent TB infection.
The tuberculin skin test, also known as the Mantoux test or PPD (purified protein derivative), is done by injecting a solution containing a protein derived from tuberculosis bacteria just under the top layer of skin on the forearm.
If the skin at the injection site develops a red, raised bump after several days, it indicates the person may be infected with TB.
Like the tuberculin skin test, the IGRA blood test measures the bodys immune response to an antigen derived from Mycobacterium tuberculosis. The test is done in a lab after a blood sample is drawn.
If active tuberculosis is suspected, the tuberculin skin test, IGRA blood test, and/or a chest x-ray may be done to help in the diagnosis.
However, neither the tuberculin skin test nor the IGRA blood test can distinguish between active and latent disease.
Additionally, the skin test can give a false-positive result if a person has had prior vaccination with the bacille Calmette-Guerin (BCG) vaccine or is infected with other bacteria that are a close relative of tuberculosis.
Chest x-rays also have their limitations, because the effects of TB on the lungs resemble those of many other conditions.
For a more definitive diagnosis, other tests are necessary:
However, culturing TB bacteria can take 4 to 7 weeks before any growth appears, making this a slow process for detecting TB.
A variety of lab tests can also be done to see which drugs will best treat the strain of tuberculosis a person has.
Imaging tests may also be used to assist in providing a diagnosis of active tuberculosis:
Because tuberculosis is closely associated with HIV, its become common practice to test for HIV in someone with suspected tuberculosis whose HIV status is not known.
This allows treatment for HIV to be started as well, if appropriate, and coordinated with TB treatment.
It can take some time to positively diagnose active tuberculosis.
In cases where tuberculosis is strongly suspected, doctors often start anti-tuberculosis treatment before the diagnosis is confirmed by laboratory isolation of the TB bacteria.
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Tuberculosis has affected humans for millennia, but no effective treatment for it existed until the mid-1800s, when the sanatorium cure was first conceived.
The sanatorium cure involved rest, fresh air, and a nutritious diet to strengthen the bodys natural defenses against the bacteria that cause TB. It also included isolation, to prevent others from becoming infected.
At the time, the disease was often referred to as "consumption" or "phthisis."
In some cases, doctors purposely collapsed all or part of a patients lung, on the theory that this would allow the lung to rest. Opinions are divided as to whether it helped.
The first anti-tuberculosis antibiotic, streptomycin, was developed in the 1940s, and the incidence of the disease in the United States and in other developed countries plummeted soon thereafter.
However, tuberculosis (TB) is still common in poorer countries, and the number of cases in the United States began to rise again in the mid-1980s, largely as a consequence of the HIV epidemic and decreased funding for public health programs in general, and TB clinics in particular.
A number of drugs can be used to treat tuberculosis. The most commonly used are:
Because so many strains of tuberculosis have developed resistance to certain antibiotics, treatment is started with the administration of at least three and preferably four different antibiotics that have activity against TB.
Lab tests known as drug susceptibility tests can determine which antibiotics will be more likely to cure a given case of TB.
Drug treatment typically lasts for at least 6 months and sometimes longer. Stopping treatment too early can result in a recurrence of the infection and can lead to the development of drug-resistant tuberculosis.
Isolation is still a part of modern tuberculosis treatment. A person with active pulmonary tuberculosis should be isolated until he or she responds to treatment and has sputum tests that are negative (by so-called acid-fast smears) on at least two occasions. This usually takes no more than two weeks.
The treatment of tuberculosis and control of the diseases spread has been complicated worldwide by the emergence of multidrug-resistant tuberculosis, defined as strains of TB that do not respond to at least isoniazid and rifampin, the two drugs that are the cornerstone of TB treatment.
To some degree, infection-causing bacteria will adapt to become resistant to certain antibiotics, evolving into superbugs that are unaffected by most antibiotics.
But to a large degree, the way in which humans have used antibiotics over the years has sped up the process.
Overuse of antibiotics for example, taking them to treat viral infections, for which they are ineffective is one of the reasons certain bacteria have become resistant to common antibiotics.
Another is failing to take a full course of antibiotics when a bacterial infection is present. When antibiotics are stopped early, the bacteria that have not yet been killed often develop resistance to the drug being used for treatment.
This is a common problem with TB treatment, where antibiotics need to be taken daily for several months.
One of the approaches public health officials have taken to combat multidrug-resistant tuberculosis is directly observed therapy, or DOT.
In DOT, a trained healthcare worker provides each dose of medication, watches the patient swallow it, and documents that the medication has been taken.
Studies show a higher cure rate among patients receiving DOT than among those self-administering their tuberculosis drugs.
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