Tuberculosis

Tuberculosis (TB) is a bacterial infection. The condition usually strikes the lungs. However, it may spread to other parts of the body as well -- particularly the brain, kidneys, heart, spine, bones or lymph nodes (small structures throughout the body that offer protection from bacteria and other organisms).


Causes/associated factors
Worldwide, tuberculosis causes an estimated 2 million deaths per year -- more than any other infectious disease. The good news is that TB is nearly always treatable.
There are two types of tuberculosis: the infection (the inactive or latent form) and the disease (the active form). The infection occurs when the bacterium Mycobacterium tuberculosis is breathed into the lungs. In most cases, the body's immune system forms a fibrous wall that contains -- but doesn't destroy -- the bacterium. This phase can last for several months, often with no symptoms. In most cases, the infection doesn't advance any further.

The disease occurs when the body's immune system can't control the bacteria, which actively invade lung tissue or other organs. This can occur during the initial infection or much later if the body's defenses weaken, allowing the contained bacteria to become active. Only about 10 percent of people infected with TB develop the disease. For at least half of those, the disease occurs within two years of the initial infection.

Certain conditions increase the risk of developing the disease, including:

a weak immune system (due to factors such as HIV infection, treatment for cancer or long-term steroid use)
substance abuse
poor nutrition and conditions associated with poor nutrition (such as intestinal bypass surgery, gastrectomy and malabsorption syndromes)
medical conditions such as diabetes, silicosis or kidney failure
an inadequately treated TB infection
In the United States, the incidence of TB steadily decreased through most of the 1900s. In the early 1980s, however, there was a significant increase thought to be associated with factors such as HIV and AIDS, homelessness, drug abuse and immigration of people with the active disease. Since 1993, the incidence of TB has been decreasing.


Transmission
Again, tuberculosis spreads through contact with airborne bacteria. A person who has active tuberculosis disease can spread the infection through activities such as coughing, sneezing, speaking or singing. Typically, those who respond well to treatment are no longer contagious within days or weeks of starting medication therapy.
People who have inactive tuberculosis infections can't spread TB.

You may have a higher risk of being exposed to the tuberculosis bacterium if you:

have contact with someone who has TB disease (The risk increases with prolonged, frequent or intense contact, especially if the person has extensive lung disease and coughs often.)
live in or emigrated from an area where TB is common, such as Africa, Asia, Latin America, Eastern Europe or Russia
live or work in an institution, such as a nursing home or other long-term residential facility, homeless shelter or prison
work in the health care field, especially with people at high risk for TB
have limited medical care
belong to certain high-risk populations, such as Hispanics, African Americans, Native Americans and the homeless
use illegal drugs
Children exposed to high-risk adults also have a higher risk of developing tuberculosis.


Signs/symptoms
Again, there are often no symptoms during the primary stage of tuberculosis infection. Some people experience mild flu-like symptoms. If you develop tuberculosis disease, symptoms vary depending on the affected body part and may include:
persistent productive cough (sometimes tinged with blood)
shortness of breath
chest pain
fever
chills
night sweats
fatigue or weakness
poor appetite
weight loss

Diagnosis
The doctor will ask questions about your medical history and do a physical exam. You may also need a variety of tests, such as a tuberculin skin test, a chest X-ray, and a sputum smear and culture. Sometimes, tuberculosis is detected through a routine tuberculin skin test or chest X-ray done for other reasons. All confirmed TB cases must be reported to the public health department.
Mantoux tuberculin skin test or purified protein derivative (PPD)
People infected with tuberculosis typically react to a low-dose tuberculin skin test within two to 10 weeks after becoming infected with tuberculosis. With this test, an injection of dead TB bacteria is given in the forearm. Forty-eight to 72 hours later, the injection site is checked for a reaction.

If you're at high risk for TB (you have HIV or had recent contact with someone who has TB), a 5-millimeter lump is considered positive. If you have other risk factors for TB (such as diabetes or being homeless), a 10-millimeter lump is considered positive. If you have no known risk factors, a 15-millimeter lump is considered positive. It's important to note that reactions may be suppressed if you're critically ill or have a weak immune system or acute infectious disease.

Most people who have positive tuberculin test results don't have active TB. Likewise, negative results don't guarantee the absence of active TB.

Two-step testing
If you were initially infected with TB a long time ago, your reaction to a current skin test may be negative. Receiving the test may stimulate your body's immune reaction, however, producing a positive result the next time you're tested. The next positive test may be mistaken for a new TB infection. To avoid this, your doctor may recommend a second TB test one to three weeks after the first. If the second test is positive after such a short time, it may indicate that you were infected long ago. This type of testing is most often used as the first test in screening people who must be tested for TB periodically, such as health care workers.

Chest X-ray
If the TB skin test is positive, you'll need a chest X-ray. If the TB bacterium has attacked your lungs, the X-ray will usually show an abnormal area. A chest X-ray alone is not enough to diagnose TB, however.

Sputum smear and culture
Tuberculosis disease can be diagnosed through lab tests of a sputum sample. First, a sample of phlegm coughed up from the lungs will be examined through a microscope for bacteria that resemble TB bacteria. This is known as a smear. Then, any bacteria detected in the phlegm will be allowed to grow in a special dish. This is known as a culture. If TB bacteria are present, they'll grow into a characteristic shape within one to three weeks, confirming the diagnosis of TB. The culture can also help determine what medications will be most effective.

Other possible tests
Under certain circumstances, you may need lab tests on samples of bone marrow or liver or other tissue. If meningitis (inflammation of the membranes surrounding the brain or spinal cord) is suspected, you may need a lumbar puncture. With this procedure, a needle is placed in the spinal cord to collect samples of spinal fluid. If a diagnosis of TB is confirmed, you'll need an HIV test.


Treatment
Most initial TB infections heal without treatment and don't progress to active disease. Depending on your age, medical history and degree of exposure to TB, an antibiotic may help reduce the risk of progressive disease or later reactivation. When preventive therapy is needed, a nine-month course of the antibiotic isoniazid is often prescribed. During this treatment, you'll need regular medical checkups. (Note: For certain people, such as those who have HIV, other medications may be preferable.)
If you have active TB, treatment is directed at curing the disease as well as minimizing the spread of the infection to others. Your doctor will recommend one of several treatment regimens consisting of three or four medications. Often, a combination of isoniazid, rifampin, pyrazinamide, and either ethambutol or streptomycin is prescribed for two months. (Medication choice depends on tests that can help the doctor determine which medication the infection is most susceptible to. Medication variety helps keep the bacteria from developing resistance to the medications.) Then, a second combination of two medications is typically prescribed for another four to seven months. Your progress may be monitored through additional sputum cultures. Depending on your response to the medications, your doctor may change the medications or add new ones. If you're HIV-positive, you'll need additional treatment.

If your doctor prescribes medication, make sure you clearly understand how to take it. If you take the medication incorrectly or inconsistently, treatment may fail and the TB bacteria may become resistant to the medications -- making the disease more difficult to treat. In fact, the best treatment results occur with directly observed therapy (DOT) in which local health department personnel actually watch you take every dose of medication.

All medications used to treat TB can be toxic to some degree, so medication choices may also vary depending on your age and whether you're pregnant or have any other medical conditions. Discuss these issues and any concerns you may have with your doctor.


Complications
Tuberculosis may spread to various organs. Other potential complications include:
chronic obstructive pulmonary disease (COPD, a disease that decreases the ability to breathe)
bronchiectasis (dilated air passages in the lungs usually accompanied by secretions of pus)
lung abscess (a collection of pus in the lung)
respiratory collapse
adverse reactions to TB medications

Pregnancy-specific information
If you're at high risk for developing TB, especially if you have HIV, consult your doctor for a skin test. Late TB diagnosis or inadequate treatment may jeopardize your baby's health.
Active tuberculosis disease increases the risk of preterm delivery and low birthweight, as well as infant mortality during the perinatal period (from the 28th week of pregnancy until 28 days after birth).

If you're diagnosed with a TB infection, preventive treatment may be postponed until after delivery, unless the TB exposure is recent or you have HIV or other moderate to high risk factors for TB. If treatment is recommended, your doctor will discuss any potential side effects. The typical medication regimen includes isoniazid, pyridoxine, rifampin and ethambutol. Streptomycin should be avoided during pregnancy, and pyrazinamide is usually not recommended.


Senior-specific information
Tuberculosis can be difficult to detect in elderly adults because some symptoms may be characteristic of aging or other conditions. Elderly adults hospitalized for pneumonia are often tested for TB, and a TB skin test is recommended before admission to a chronic care facility.

Prevention
To prevent tuberculosis, avoid close contact with anyone who's infected. If that's not possible or you suspect you've been exposed to TB, consult your doctor for testing.
If you have tuberculosis disease, you can help prevent its spread to others. Take your medication regularly and as prescribed. It often helps to take the medication at the same time every day, using a dispenser or marking a calendar as a reminder. You may want to have a family member help you. If your local health department offers directly observed therapy, participate in the program to help you take your TB medications consistently. Again, this form of therapy is the most successful.

Remember that you're considered contagious during initial medication therapy, so restrict your activity during this time to avoid spreading the disease. Wash your hands regularly, properly dispose of used tissues, and cover your mouth and nose when sneezing, laughing or coughing. Make sure you have good indoor ventilation and get plenty of fresh air. Your doctor may recommend wearing a protective mask when you're in public.

In countries where TB is prevalent, BCG (a TB vaccine not extensively used in the United States) may be given to infants and small children. BCG hasn't been shown to provide consistent protection from TB. People vaccinated with BCG may have positive test results with the TB skin test. Research on the development of an effective tuberculosis vaccine continues.