Facts on Tuberculosis (TB)
Purified Protein Derivative (PPD) Procedure for Detecting Tuberculosis by MedicineNet
Tuberculosis (TB) describes an infectious disease that has plagued humans since the Neolithic times. Two organisms cause tuberculosis -- Mycobacterium tuberculosis and Mycobacterium bovis.
Physicians in ancient Greece called this illness "phthisis" to reflect its wasting character. During the 17th and 18th centuries, TB caused up to 25% of all deaths in Europe. In more recent times, tuberculosis has been called "consumption."
- Robert Koch isolated the tubercle bacillus in 1882 and established TB as an infectious disease.
- In the 19th century, patients were isolated in sanatoria and given treatments such as injecting air into the chest cavity. Attempts were made to decrease lung size by surgery called thoracoplasty.
- During the first half of the 20th century, no effective treatment was available.
- Streptomycin, the first antibiotic to fight TB, was introduced in 1946, and isoniazid (Laniazid, Nydrazid), originally an antidepressant medication, became available in 1952.
- M. tuberculosis is a rod-shaped, slow-growing bacterium.
- M. tuberculosis' cell wall has high acid content, which makes it hydrophobic, resistant to oral fluids.
- The cell wall of Mycobacteria absorbs a certain dye used in the preparation of slides for examination under the microscope and maintains this red color despite attempts at decolorization, hence the name acid-fast bacilli.
- M. tuberculosis continues to kill millions of people yearly worldwide.
- Most TB cases occur in developing nations that have poor hygiene, limited health-care resources, and high numbers of people infected with HIV.
- In the United States, the incidence of TB began to decline around 1900 because of improved living conditions.
- TB cases have increased since 1985, most likely due to the increase in HIV infection.
- Tuberculosis continues to be a major health problem worldwide. In 2008, the World Health Organization (WHO) estimated that one-third of the global population was infected with TB bacteria.
- With the spread of AIDS, tuberculosis continues to lay waste to large populations. The emergence of drug-resistant organisms threatens to make this disease once again incurable.
- In 1993, the WHO declared tuberculosis a global emergency.
What Are Causes of Tuberculosis?
All cases of TB are passed from person to person via droplets. When someone with TB infection coughs, sneezes, or talks, tiny droplets of saliva or mucus are expelled into the air, which can be inhaled by another person.
- Once infectious particles reach the alveoli (small saclike structures in the air spaces in the lungs), another cell, called the macrophage, engulfs the TB bacteria.
- Then the bacteria are transmitted to the lymphatic system and bloodstream and spread to other organs occurs.
- The bacteria further multiply in organs that have high oxygen pressures, such as the upper lobes of the lungs, the kidneys, bone marrow, and meninges -- the membrane-like coverings of the brain and spinal cord.
- When the bacteria cause clinically detectable disease, you have TB.
- People who have inhaled the TB bacteria, but in whom the disease is controlled, are referred to as infected. Their immune system has walled off the organism in an inflammatory focus known as a granuloma. They have no symptoms, frequently have a positive skin test for TB, yet cannot transmit the disease to others. This is referred to as latent tuberculosis infection or LTBI.
- Risk factors for TB include the following:
- HIV infection,
- low socioeconomic status,
- crowded living conditions,
- diseases that weaken the immune system,
- migration from a country with a high number of cases,
- and health-care workers.
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What Are Symptoms and Signs of Tuberculosis?
You may not notice any symptoms of illness until the disease is quite advanced. Even then the symptoms -- loss of weight, loss of energy, poor appetite, fever, a productive cough, and night sweats -- might easily be blamed on another disease.
- Only about 10% of people infected with M. tuberculosis ever develop tuberculosis disease. Many of those who suffer TB do so in the first few years following infection. However, the bacillus may lie dormant in the body for decades.
- Although most initial infections have no symptoms and people overcome them, they may develop fever, dry cough, and abnormalities that may be seen on a chest X-ray.
- This is called primary pulmonary tuberculosis.
- Pulmonary tuberculosis frequently goes away by itself, but in more than half of cases, the disease can return.
- Tuberculous pleuritis may occur in some people who have the lung disease from tuberculosis.
- The pleural disease occurs from the rupture of a diseased area into the pleural space, the space between the lung and the lining of the chest and abdominal cavities. This is often quite painful since all of the pain fibers of the lung are located in the pleura.
- These people have a nonproductive cough, chest pain, and fever. The disease may go away and then come back at a later date.
- In a minority of people with weakened immune systems, TB bacteria may spread through their blood to various parts of the body.
- This is called miliary tuberculosis and produces fever, weakness, loss of appetite, and weight loss.
- Cough and difficulty breathing are less common.
- Generally, return of dormant tuberculosis infection occurs in the upper lungs. Symptoms include
- common cough with a progressive increase in production of mucus and
- coughing up blood.
- Other symptoms include the following:
- Some people may develop tuberculosis in an organ other than their lungs. About a quarter of these people usually had known TB with inadequate treatment. The most common sites include the following:
- lymph nodes,
- genitourinary tract,
- bone and joint sites,
- meninges, and
- the lining covering the outside of the gastrointestinal tract.
What Tests Do Doctors Use to Diagnose Tuberculosis?
The doctor will complete the following tests to diagnose tuberculosis. You may not be hospitalized for either the initial tests or the beginning of treatment.
- Chest X-ray: The most common diagnostic test that leads to the suspicion of infection is a chest X-ray.
- In primary TB, an X-ray will show an abnormality in the mid and lower lung fields, and lymph nodes may be enlarged.
- Reactivated TB bacteria usually infiltrate the upper lobes of the lungs.
- Miliary tuberculosis exhibits diffuse nodules at different locations in the body.
- The Mantoux skin test also known as a tuberculin skin test (TST or PPD test): This test helps identify people infected with M. tuberculosis but who have no symptoms. A doctor must read the test.
- The doctor will inject 5 units of purified protein derivative (PPD) into your skin. If a raised bump of more than 5 mm (0.2 in) appears at the site 48 hours later, the test may be positive.
- This test can often indicate disease when there is none (false positive). Also, it can show no disease when you may in fact have TB (false negative).
- QuantiFERON-TB Gold test: This is a blood test that is an aid in the diagnosis of TB. This test can help detect active and latent tuberculosis. The body responds to the presence of the tuberculosis bacteria. By special techniques, the patient's blood is incubated with proteins from TB bacteria. If the bacteria is in the patient, the immune cells in the blood sample respond to these proteins with the production of a substance called interferon-gamma (IFN-gamma). This substance is detected by the test. If someone had a prior BCG vaccination (a vaccine against TB given in some countries but not the U.S.) and a positive skin test due to this, the QuantiFERON-TB Gold test will not detect any IFN-gamma.
- Sputum testing: Sputum testing for acid-fast bacilli is the only test that confirms a TB diagnosis. If sputum (the mucus you cough up) is available, or can be induced, a lab test may give a positive result in up to 30% of people with active disease.
- Sputum or other bodily secretions such as from your stomach or lung fluid can be cultured for growth of mycobacteria to confirm the diagnosis.
- It may take one to three weeks to detect growth in a culture, but eight to 12 weeks to be certain of the diagnosis.
When Should Someone Seek Medical Care for Tuberculosis?
If someone among your family or close associates is found to be sick with active TB, you should see your doctor and be tested for tuberculosis.
- The dangerous contact time is before treatment. However, once treatment with drugs starts, the sick person is noncontagious within a few weeks.
- If you develop any side effects from medications prescribed to treat tuberculosis -- such as itching, change in color of skin, tiredness, visual changes, or excessive fatigue -- call your doctor immediately.
What Are Treatment Options for Tuberculosis (TB)?
Today, doctors treat most people with TB outside the hospital. Gone are the days of going to the mountains for long periods of bed rest. Doctors seldom use surgery.
- Doctors will prescribe several special medications that you must take for six to nine months.
- Standard therapy for active TB consists of a six-month regimen:
- Treatment takes that long because the disease organisms grow very slowly and, unfortunately, also die very slowly. (Mycobacterium tuberculosis is a very slow-growing organism and may take up to six weeks to grow in a culture media.)
- Doctors use multiple drugs to reduce the likelihood of resistant organisms emerging.
- Often the drugs will be changed or chosen based on the laboratory results.
- If doctors doubt that you are taking your medicine, they may have you come to the office for doses. Prescribing doses twice a week helps assure compliance.
- The most common cause of treatment failure is people's failure to comply with the medical regimen. This may lead to the emergence of drug-resistant organisms. You must take your medications as directed, even if you are feeling better.
- Another important aspect of tuberculosis treatment is public health. This is an area of community health for which mandated treatment can occur. In some cases, the local health department will supervise administration of the medication for the entire course of therapy.
- Doctors likely will contact or trace your relatives and friends.
- Your relatives and friends may need to undergo appropriate skin tests and chest X-rays.
Is It Possible to Prevent Tuberculosis?
- Treatment to prevent active TB from developing in a person with a latent tuberculosis infection (LTBI) aims to kill walled-up germs that are doing no damage right now but could break out (activate) years from now.
- If you should be treated to prevent sickness, your doctor usually prescribes a daily dose of isoniazid (also called INH), an inexpensive TB medicine.
- You will take INH for up to a year, with periodic checkups to make sure you are taking it as prescribed and that it is not causing undesirable side effects. In some cases, intolerance or allergic response can mandate an alternative treatment that may go on for 18 months.
- Treatment also can stop the spread of TB in large populations.
- The tuberculosis vaccine, known as bacille Calmette-Guérin (BCG) may prevent the spread of tuberculosis and tuberculous meningitis in children, but the vaccine does not necessarily protect against pulmonary tuberculosis. It can, however, result in a false-positive tuberculin skin test that in many cases can be differentiated by the use of the QuantiFERON-TB Gold test mentioned above.
- Health officials generally recommend the vaccine in countries or communities where the rate of new infection is greater than 1% per year. BCG is not generally recommended for use in the United States because there is a very low risk of tuberculosis infection. It may be considered for very select patients at high risk for tuberculosis and who meet special criteria.
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What Is Drug-Resistant TB?
- Most strains of the TB bacteria require at least two drugs for treatment to prevent resistance.
- Resistance is caused by inconsistent or partial treatment. In some instances, patients are prescribed inadequate therapy or enough drug is not available. Usually this occurs because patients tend to stop taking their medication once they start to feel better. Observed therapy is often required and monitored by health departments in the U.S.
- Multidrug-resistant TB (MDR-TB) is caused by a bacteria that is resistant to at least isoniazid and rifampicin. Prolonged alternative therapy is required to treat this form of TB, often for up to two years.
- Extensively drug-resistant TB (XDR-TB) is rare but extremely problematic. This form of TB is very difficult to treat and often requires prolonged isolation of the individual to protect the community at large. If TB is treated properly and consistently, these resistant forms are much less likely to spread.
What Is the Prognosis for Tuberculosis?
You can expect to keep your job, to stay with your family, and to lead a normal life if you contract tuberculosis. However, you must take your medicine regularly to be sure of a cure and to prevent others from being infected.
- With treatment, your chance of full recovery is very good. The importance of following the prescribed medication regimen cannot be overemphasized. Noncompliance with the medication regimen is the major cause of treatment failure.
- Without treatment, the disease will progress and lead to disability and death.
U.S. Centers for Disease Control and Prevention. "Decrease in Reported Tuberculosis Cases -- United States, 2009." MMWR 59.10 (2010): 289-294.
U.S. Centers for Disease Control and Prevention. "Updated Guidelines for Using Interferon Gamma Release Assays to Detect Mycobacterium tuberculosis Infection -- United States,
2010." MMWR 59 (No. RR-5)
June 25, 2010: 1-25.