Tuberculosis (TB)

What is tuberculosis?

Tuberculosis, or TB, has been around for a long time -- the ancient Greek physician Hippocrates wrote about it, and TB germs have been found in Egyptian mummies and in bones dating back 5,000 years. Also called consumption and the "great white plague," TB was a leading cause of death in Europe and America until as recently as the 1940s. In the days before antibiotics, TB patients would go to sanitariums for rest and fresh air.

Since the discovery of antibiotics, TB rates have declined dramatically but the disease is still a major health problem around the world, causing some 1.7 million deaths a year. Today, nearly one out of three people worldwide is infected with Mycobacterium tuberculosis, the bacterium that causes TB.

In the U.S., reported cases of TB have been declining steadily in recent years (from more than 26,000 in 1992 to 11,545 in 2009). This doesn't tell the whole story, though. An estimated 11 million healthy Americans are infected with the TB bacterium, and about 10 percent will develop the disease at some point in their lives. In fact, estimates show that only one quarter of people infected with TB in this country have even been diagnosed.

What causes TB?

In simplest terms, if the TB germ is present in your lungs, you have TB. But that doesn't necessarily mean you'll feel sick. If your immune system is doing its job, the germ should not cause much trouble. You might experience some coughing after the initial infection, but you probably won't have any symptoms. Most importantly, you won't be able to infect anyone else. This is called latent TB.

Sometimes, latent TB can turn into active TB. If your immune system ever gets weakened, or if you're healthy and your immune defenses simply fail, the germ can start multiplying. It usually attacks lung tissue, but can also target other parts of your body, such as the joints, bones, urinary tract, or central nervous system. Even at this point, symptoms might be barely noticeable, but the infection will be contagious. About 10 percent of all latent TB infections eventually become active.

How contagious is TB and how does it spread?

Unlike the flu or the common cold, TB generally doesn't spread among strangers on buses or in the checkout line at the grocery store. To catch the disease, it often takes long-term contact, such as spending several hours per day with a person who has an active infection.

TB spreads through the air when a person with active TB disease coughs. Not surprisingly, the disease tends to spread most quickly in crowded and poorly ventilated places, including prisons and homeless shelters.

Who is most at risk?

Anyone who spends a lot of time around someone with an active case of the disease is a target for TB infection. People living or working in health-care facilities, nursing homes, homeless shelters, juvenile detention centers, or prisons are also at higher risk, and should be tested for TB.

Almost all TB infections eventually become active in people with HIV/AIDS, and TB is the leading cause of death in HIV/AIDS patients. For similar reasons, people who have weakened immune systems because of cancer treatment, malnutrition, or substance abuse are also at increased risk.

Also, people with diabetes who are infected with TB have a three times greater chance of developing active TB. (That translates to a 30 percent overall lifetime risk versus 10 percent in otherwise healthy infected people).

According to the CDC, Hispanics accounted for 29 percent of the total reported U.S. cases in 2009, African Americans and non-Hispanic blacks another 28 percent, Asians 28% and whites 16%.

TB germs are especially common in parts of Africa, Latin American, Asia, and Eastern Europe. By the latest estimates, about 60 percent of the people in the United States with latent TB were born in another country. Among foreign-born people with TB in this country, the top countries of origin are Mexico, the Philippines, Vietnam, India, and China.

Also, people of any age can be infected, but the highest case rates are seen among those age 65 and older.

What are the symptoms of active tuberculosis?

It's worth repeating that latent or inactive TB won't cause any symptoms. Even if the disease becomes active and contagious, symptoms can be mild or even nonexistent. But if an active case of TB becomes serious enough, the signs will be impossible to ignore.

Like other infections of the lungs, tuberculosis can trigger coughing. Symptoms of TB include: a cough that lasts at least three weeks, coughing up discharge or "sputum" from the lungs that looks dark or bloody, and pain in the chest. Other symptoms can include weight loss, loss of appetite, mild fever, weakness or fatigue, chills, and sweating at night.

If not treated in time, active TB can lead to serious complications including permanent lung damage. The bacteria can spread to the bone, kidneys, brain (meningeal TB), and whole body (miliary TB). In some cases, it can be fatal: In 2006, TB killed 644 people in the United States.

How is TB diagnosed?

TB exposure is usually diagnosed with a simple skin test. A doctor or nurse injects a small amount of a substance called tuberculin under the skin, and the injection site is checked 48 to 72 hours later. A raised red bump of a certain size is considered a positive reaction, which means you've probably been exposed to TB bacteria at some point in your life. A positive does not necessarily mean you have an active infection.

In some countries, the BCG vaccine is used against TB. Anyone vaccinated will have a positive tuberculin skin test, which produces a lot of false positive results. People with HIV may also have false-positives because the test cross-reacts with other mycobacteria. The test may also fail to pick up infections (give false negatives), especially among recently infected elderly or immunocompromised people.

In 2005, the Food and Drug Administration approved a blood test for TB called QuantiFERONTB Gold test (QFT-G). It can be used instead of the skin test and has some advantages. For example, you don't have to go back to have the result read, it isn't affected by BCG vaccination, and the result isn't a subjective decision by the doctor or nurse. On the other hand, it's not in wide use yet so it isn't clear how reliable it is to use for testing children and immunocompromised patients. If the screening test is positive, a doctor may order a chest x-rays to see if the disease is active, and may order a sputum culture to look for bacteria.

How is it treated?

Like other bacterial diseases, TB can be treated with antibiotics. Currently, about 1.2 percent of cases are resistant to two commonly used drugs (isoniazid and rifampin). Because drug-resistant TB is considered such a public-health threat, doctors in the U.S. are required to take a sample of a patient's sputum to determine what type of germs they are dealing with.

If a healthy person tests positive on the TB screening test, in some cases doctors may decide to put off treatment. Most of the time, doctors will prescribe antibiotics to treat latent tuberculosis infection -- especially if the patient has a weak immune system, lives with someone who has TB, or otherwise has a high chance of developing active TB. Treatment of latent tuberculosis infection greatly reduces the chances that the infection will progress to active tuberculosis disease. It is also usually easier to treat latent tuberculosis infection. The preferred treatment is isoniazid for nine months.

Patients with active cases of TB that don't show any sign of resistance are treated with a combination of antibiotics. The initial treatment phase lasts two months, followed by further tests (generally, sputum culture, and chest x-rays). Depending on the results of the tests, the patient then usually receives an additional four to seven months (a total of six to nine months) of antibiotic treatment.

For patients with multiple drug-resistant TB or, even worse, extensively drug-resistant TB, the options are more limited. Doctors will have to try combinations of powerful medications for many months to have any chance of treating the disease. Many patients will recover, but the whole process will be more complicated and costly, and the outcome is less certain. (For more information on drug-resistant TB, see our special report.)

Whatever your doctor prescribes, it's important to take every pill as directed. If you start missing doses or stop taking your medication too soon, you'll give the germs a chance to rally -- and worse, build up resistance to antibiotics. Every pill is so important that many health departments hire workers to watch patients take their daily dose of medications.

Some antibiotics used to treat TB have side effects, so depending on what you're taking and what other medical conditions you have, your doctor may want to do regular blood tests or prescribe certain vitamins. Avoid drinking alcohol while taking antibiotics, and if you experience side effects such as nausea, stomach pain, blurred vision, or jaundice, contact your doctor. (Side effects will vary depending on the drugs you take. Check with your doctor or pharmacist.)

How can we stop the spread of TB?

If you have active TB, taking all the medication that your doctor prescribes -- even if you feel better -- is the most important thing you can do to protect others. Patients with active TB are still contagious for at least two or three weeks after treatment starts.

As long as your doctor says you're contagious, stay home from school or work and avoid close contact with family members, especially young children. If at all possible, sleep by yourself in a well-ventilated room. Always cover your mouth with a tissue when you cough, and seal the tissue in a closed bag before throwing it away.

Local health departments may ask your close contacts and family members to be tested. If they test positive, they should be treated as well. If your family includes someone who may not have a robust immune system -- such as someone who is HIV-positive or a young child -- they may be treated even if they test negative.

References

Nebraska Department of Health and Human Service: History of Tuberculosis

World Health Organization: Tuberculosis Fact Sheet. November 2010.

CDC National Center for HIV, STD, and TB Prevention. Self-Study Modules on Tuberculosis

Bennett DE et al. Prevalence of tuberculosis infection in the United States population: The national health and nutrition examination survey, 1999-2000. American Journal of Respiratory Critical Care Medicine. February 2008. 177(3): 348-355.

Mayo Clinic. Tuberculosis. January 29, 2009.

Centers for Disease Control and Prevention. Questions and Answers about TB, November 24, 2010.

National Institute of Allergy and Infectious Disease. Tuberculosis: Detailed explanation of TB. 2007.

American Lung Association. Tuberculosis skin test fact sheet.

CDC Treatment of Latent Tuberculosis Infection (LTBI).

American Academy of Family Physicians. Tuberculosis: Treatment of Tuberculosis Infection. February 2010.

CDC Reported Tuberculosis in the United States, 2006. Executive Summary.

CDC Trends in Tuberculosis United States, October 27, 2010.

Public Health Agency of Canada. Tuberculosis fact sheet: How is TB spread?

CDC National Center for HIV, STD, and TB Prevention QuantiFERON-TB Gold Test.

Merck Manual Professional. Tuberculosis (TB).

Joint Committee of the American Thoracic Society, the Infectious Disease Society of America, and CDC. Treatment of tuberculosis. 2003.

CDC. Tuberculosis: Data and Statistics. October 25, 2010.

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