Original Article: http://www.mayoclinic.com/health/tuberculosis/DS00372
Tuberculosis (TB) is a life-threatening infection that primarily affects your lungs. Every year, tuberculosis kills nearly 2 million people worldwide. The infection is common — about one-third of the human population is infected with TB, with one new infection occurring every second.
Tuberculosis has plagued human beings for millennia. Signs of tubercular damage have been found in Egyptian mummies and in bones dating back at least 5,000 years. Today, despite advances in treatment, TB is a global pandemic, fueled by the spread of HIV/AIDS, poverty, a lack of health services and the emergence of drug-resistant strains of the bacterium that causes the disease.
Tuberculosis spreads through airborne droplets when a person with the infection coughs, talks or sneezes. In general, you need prolonged exposure to an infected person before becoming infected yourself. Even then, you may not develop symptoms of the disease. Or, symptoms may not show up until many years later.
Left untreated, tuberculosis can be fatal. With proper care, however, most cases of tuberculosis can be treated, even those resistant to the drugs commonly used against the disease.
Signs and symptoms
Although your body may harbor the TB bacteria, your immune system often can prevent you from becoming sick. For that reason, doctors make a distinction between:
Your immune system begins to attack TB bacteria two to eight weeks after you're infected. Sometimes the bacteria die, and the infection clears completely. In other cases, the bacteria remain in your body in an inactive state and cause no tuberculosis symptoms. In still other cases, you may develop active TB.
TB mainly affects your lungs (pulmonary tuberculosis), and coughing is often the only indication of infection initially. Signs and symptoms of active pulmonary TB include:
Tuberculosis also can target almost any part of your body, including your joints, bones, urinary tract, central nervous system, muscles, bone marrow and lymphatic system.
When TB occurs outside your lungs, signs and symptoms vary, depending on the organs involved. For example, tuberculosis of the spine may result in back pain, and tuberculosis that affects your kidneys might cause blood in your urine. Tuberculosis can also spread through your entire body, simultaneously attacking many organ systems.
Mycobacterium tuberculosis, the bacterium that causes tuberculosis,spreads in microscopic droplets that are released into the air when someone with the untreated, active form of the disease coughs, speaks, laughs, sings or sneezes.
Although tuberculosis is contagious, it's not especially easy to catch. In general, you need long-term contact with an infected person to become infected yourself. You're much more likely to contract tuberculosis from a family member or close co-worker than from a stranger on a bus or in a restaurant. A person with nonresistant active TB who's been effectively treated for at least two weeks is generally no longer contagious. Rarely, a pregnant woman with an active TB disease may pass the bacteria to her fetus.
TB infection versus active TB
But sometimes your immune defenses fail, even if you're otherwise healthy and don't have a compromised immune system. In that case, TB bacteria actually begin to exploit macrophages for their own survival, causing the white blood cells to form into tightly packed groups called granulomas. The bacteria multiply inside the granulomas, which eventually may enlarge into noncancerous tumor-like nodules. The centers of these nodules have the consistency of soft, crumbly cheese.
Over time, the centers can liquefy and break through the granulomatous wall surrounding them, spilling bacteria into your lungs' airways and causing large air spaces (cavities) to form (active TB). Filled with oxygen, the air spaces make an ideal breeding ground for the bacteria, which multiply in enormous numbers. The bacteria may then spread from the cavities to the rest of your lungs as well as to other parts of your body.
Active TB is contagious and serious
Without treatment, many of the people with active TB die. Those who survive develop chronic, debilitating symptoms, such as chest pain and a cough with bloody sputum, or their immune system recovers and the disease goes into remission.
Sometimes active TB can develop years after the initial infection. This occurs when your immune system can't keep dormant TB bacteria at bay, and the walled-off germs become active. A number of factors can weaken your immune system, including aging, drug or alcohol abuse, malnutrition, chemotherapy, prolonged use of prescription medications such as corticosteroids, and diseases such as HIV/AIDS. About one in 10 people who have TB infection goes on to develop active TB sometime inhis or her life. The risk is greatest in the first year after infection, but the disease may not resurface for decades.
Why is TB on the rise?
The situation in other countries is far worse. Overall, about one-third of the world's population is infected with tuberculosis. New infections and deaths from the disease are increasing. Hardest hit are sub-Saharan Africa and Southeast Asia. A number of factors have contributed to the global TB crisis, but the leading cause is the spread of HIV, the virus that causes AIDS. Tuberculosis and HIV have a deadly relationship — each fuels the progress of the other.
Infection with HIV suppresses the immune system, making it difficult for the body to control TB bacteria. As a result, people with HIV are many times more likely to progress from dormant to active disease than are people who aren't HIV-positive.
TB is one of the leading causes of death among people living with AIDS — not only because they're more susceptible to TB, but also because TB can increase the rate at which the AIDS virus replicates. One of the first indications of HIV infection may be the sudden onset of TB — often in a site outside the lungs (extrapulmonary TB).
Other factors contributing to the spread of TB in the United States and elsewhere include:
Anyone of any age, race or nationality can contract TB, but certain factors increase your risk of the disease. These factors include:
When to seek medical advice
See your doctor immediately if you have a fever, unexplained weight loss, night sweats and a persistent cough. These are often signs of TB, but they can also result from other medical problems. Your doctor can perform tests to help determine the cause. TB can be diagnosed by your primary care doctor as well as by a doctor who specializes in lung diseases (pulmonologist) or by an infectious disease specialist. If you don't have a doctor, your local public health department can help.
Even if you don't have signs or symptoms, experts advise being tested for TB if you:
Screening and diagnosis
The most commonly used diagnostic tool for TB is a simple skin test. Although there are two methods, doctors consider the Mantoux test the more accurate.
For the Mantoux test, a small amount of a substance called PPD tuberculin is injected within the skin of your inside forearm. You should feel only a slight needle prick. Within 48 to 72 hours, a health care professional will check your arm for a local reaction to the injected material. Depending on your response, the test is diagnosed as positive or negative. A positive response — usually shown by a hard, raised bump at the injection site — means you're likely to have TB infection.
The Mantoux test isn't perfect — it's possible to have either a false-positive or false-negative test. A false-positive test suggests that you have TB when you really don't. This is most likely to occur if you're infected with a mycobacterium other than the one that causes TB or if you've ever been vaccinated with bacillus Calmette-Guerin, also known as BCG, a TB vaccine that's seldom used in the United States, but widely used in countries with high TB infection rates.
A blood test that detects the presence of TB bacteria has been approved by the Food and Drug Administration. Called QuantiFERON-TB Gold (QFT) , results may be available in as soon as one day. The test is not yet widely available, however.
Researchers in October 2006 also reported encouraging results from another test under investigation for use primarily in developing countries. It's called the microscopic-observation drug-susceptibility (MODS) assay and relies on sputum samples to detect the presence of TB bacteria. MODS produces very accurate results in as little as seven days. Additionally, the test can identify drug-resistant strains of the TB bacteria.
These tests may include:
Although it takes longer, samples may also be sent to a laboratory where they're examined under a microscope as well as placed on a special medium that encourages the growth of bacteria (culture). The bacteria that appear are then tested to see if they respond to the medications commonly used to treat TB. Your doctor uses the results of the culture tests to prescribe the most effective medications for you.
What if my test is negative?
Diagnosing TB in children
Diagnosing TB in people with HIV/AIDS
Pulmonary TB can cause permanent lung damage when it's not diagnosed and treated early. Untreated active disease can also spread to other parts of the body where it can lead to serious or life-threatening complications. TB that infects the bone, for example, can cause severe pain, abscesses and joint destruction.
Meningeal TB , which occurs when TB infects your brain and central nervous system, and miliary TB , which occurs when TB bacteria spread throughout your entire body, are particularly dangerous forms of the disease. Children are especially susceptible to both meningeal TB and miliary TB.
Until the mid-20th century, people with tuberculosis were routinely cared for in sanitariums — often for years — where the clear, cold air, abundant food and enforced rest were believed to heal the lungs and halt the wasting that's characteristic of the disease. Often, the treatment not only helped cure TB, but also prevented its spread.
Today, medications are the cornerstone of tuberculosis treatment. The therapy is lengthy. Normally, you take antibiotics for six to 12 months to completely destroy the bacteria. The exact drugs and length of treatment depends on your age, overall health, the results of susceptibility tests, and whether you have TB infection or active TB.
Treating TB infection
Treating active TB disease
Sometimes the drugs may be combined in a single tablet such as Rifater, which contains isoniazid, rifampin and pyrazinamide. This makes your therapy less complicated while ensuring that you get the different drugs needed to completely destroy TB bacteria.
Another drug that may make treatment easier is rifapentine (Priftin), which is taken just once a week during the last four months of therapy. Sometimes you may be hospitalized for the first two weeks of therapy or until tests show that you're no longer contagious.
Completing treatment is essential
In an effort to help people stick with their treatment regimen, some doctors and clinics use a program called directly observed therapy short-course (DOTS). In this approach, a nurse or other health care professional administers your medication so that you don't have to remember to take it on your own.
Treatment side effects
Treating drug-resistant TB
Both strains develop as a result of partial or incomplete treatment — either because people skip doses or don't finish their entire course of medication or because they're given the wrong treatment regimen. This gives bacteria time to undergo mutations that can resist treatment with first-line TB drugs.
MDR-TB can be treated. But it requires at least two years of therapy with second-line medications that can be highly toxic. Even with treatment, many people with MDR-TB may not survive. And when treatment is successful, people with this form of TB may need surgery to remove areas of persistent infection or repair lung damage.
Treating these resistant forms of TB is far more costly than treating nonresistant TB, making therapy unaffordable in many parts of the world.
Because these resistant infections are spreading and could potentially make all TB incurable, some experts believe that ineffective treatment is ultimately worse than no treatment at all.
Treating people who have HIV/AIDS
To avoid interactions, people living with both HIV and TB may stop taking protease inhibitors while they complete a short course of TB therapy that includes rifampin. Or they may be treated with a TB regimen in which rifampin is replaced with another drug that's less likely to interfere with AIDS medications. In such cases, doctors carefully monitor the response to therapy, and the duration and type of regimen may change over time.
Without treatment, most people living with both HIV and TB will die, often in a matter of months. In such cases, the primary cause of death is TB, not AIDS.
In general, TB is a preventable disease. From a public health standpoint, the best way to control TB is to diagnose and treat people with TB infection before they develop active disease and to take careful precautions with people hospitalized with TB. But there are also measures you can take on your own to help protect yourself and others:
To help keep your family and friends from getting sick if you have active TB:
Undergoing treatment for TB for a long period of time can be complicated, yet sticking with therapy is the only way to cure the disease. You may find it helpful to have your medication administered by a nurse or other health care professional so that you don't have to remember to take it on your own. In addition, try to maintain your normal activities and hobbies and stay connected with family and friends.
Keep in mind that your physical health can directly impact your mental health. Denial, anger and frustration are not uncommon when you learn life has dealt you something difficult and unexpected. At times, you may need more tools to deal with these or other emotions. Professionals, such as therapists or behavioral psychologists, may help you put things in perspective.
By Mayo Clinic Staff
Dec 21, 2006 © 1998-2007 Mayo Foundation for Medical Education and Research (MFMER). All rights reserved. A single copy of these materials may be reprinted for noncommercial personal use only. "Mayo," "Mayo Clinic," "MayoClinic.com," "EmbodyHealth," "Reliable tools for healthier lives," "Enhance your life," and the triple-shield Mayo Clinic logo are trademarks of Mayo Foundation for Medical Education and Research.