How is TB spread?
TB is spread through the air from one person to another. When a person with TB disease of the lungs or throat coughs, sneezes or even speaks, the TB bacteria enter the air, and people nearby might breathe in these bacteria and become infected.

When a person breathes in TB bacteria, the bacteria can settle in the lungs and begin to multiply. From there, they can move through the blood to other parts of the body, like the kidney, spine, and brain.

TB in the lungs or throat can be infectious. This means that the bacteria can be spread to other people. TB in other parts of the body usually is not infectious.

How much of a threat is TB?
According to the World Health Organization, TB infection is currently spreading at the rate of one person per second. The disease kills more young people and adults than any other infectious disease and is the world's biggest killer of women. In 1993, WHO declared TB to be a global health emergency. Each year, an estimated eight million to 10 million people contract the disease and about two million people die from it. About one-third of the world's population -- or approximately two billion people -- carry the TB bacteria but most never develop the active disease. Around 10% of people infected with TB actually develop the disease at some point during their lives, but this proportion is changing because of HIV. HIV severely weakens the human immune system and makes people much more vulnerable to TB infection.

What is latent TB infection?
Most people who become infected with TB are able to fight the bacteria and stop them from multiplying. The bacteria become inactive, but they remain alive in the body and can become active later. This is called latent TB infection. People with latent TB infection have no symptoms, cannot spread TB to others, usually have a positive skin test reaction and can develop TB disease later in life if they do not receive treatment for latent TB infection. 

Many people who have latent TB infection never develop TB disease. In these people, the TB bacteria remain inactive for a lifetime without causing disease. But in other people, especially people who have weakened immune systems, the bacteria usually become active and cause TB.

What is TB disease?
TB bacteria become active if the immune system cannot stop them from multiplying. The active bacteria begin to multiply in the body and cause TB disease. Some people develop TB disease soon after becoming infected, before their immune system can fight the TB bacteria. Other people might get sick later, when their immune systems become weak for some reason.

What are some of the symptoms of TB disease?
Although people with latent TB infection do not have symptoms and cannot spread TB to others, people with active TB disease may spread TB. People with active TB disease may have an abnormal chest x-ray, a positive sputum smear or culture, and may experience some of the following symptoms:

• a bad cough that lasts longer than two weeks
• chest pain
• coughing up blood or sputum
• weakness or fatigue
• weight loss
• no appetite
• chills
• fever
• sweating at night

How is TB disease treated?
TB can almost always be cured with medicine. The most common medicines used to treat TB are:

• isoniazid (INH)
• rifampin (RIF)
• pyrazinamide (PZA)
• ethambutol (EMB)
• streptomycin (SM)

Treatment for TB depends on whether a person has active TB or latent TB infection. A person who has become infected with TB but does not have active TB might be given preventive therapy. Preventive therapy aims to kill TB bacteria that currently are inactive to prevent them from causing active TB disease in the future.
If a doctor decides a person should have preventive therapy, the usual prescription is a daily dose of INH. The person takes INH for six to nine months -- possibly up to a year for some patients --with periodic checkups to make sure the medicine is being taken as prescribed.

However, when a patient has active TB, several different medicines are needed. Taking several drugs together will do a better job of killing all of the bacteria and preventing them from becoming resistant to the drugs. Many medications are available in fixed-dose combinations (FDC), which combine several medications into a single tablet. WHO strongly recommends the use of FDC tablets for TB treatment.
Patients commonly receive a combination of several drugs -- most frequently INH plus two to three others -- usually for at least six months. The patient will probably notice improvements only a few weeks after starting to take the drugs.

It is very important that patients take their medicine correctly for the full length of treatment. If the medicine is taken incorrectly or treatment is stopped, the patient might become sick again and will be able to infect others with TB. If the treatment is not completed, the TB bacteria might become resistant to the medications. As a result, many public health authorities recommend DOTS, or directly observed treatment, short-course, where a health care worker ensures that patients are taking their treatment regimens properly.
Regular checkups are needed to monitor treatment progression. Sometimes the medicines used to treat TB can cause side effects. It is important that people undergoing both preventive therapy and treatment for TB disease immediately inform a doctor if they begin having any unusual symptoms.

The treatment of tuberculosis in people infected with HIV requires close monitoring. It is especially important for HIV-positive people to discuss TB treatment options with a health care worker to avoid potential complications, because some commonly prescribed medications to treat TB can interact with some antiretroviral drugs.
The standard treatment regimen for TB patients who previously have been treated for the disease also may differ. Re-treatment cases also should be closely monitored because they have a higher likelihood of drug resistance, making treatment more difficult.

What is DOTS?
Directly observed treatment, short-course, or DOTS, is the internationally recommended strategy to control TB. DOTS has five components:

• political commitment to sustained TB control
• access to quality-assured TB sputum microscopy
• standardized short-course drug treatment, including direct observation of therapy
• an uninterrupted supply of quality-assured drugs
• a standardized recording and reporting system, enabling assessment of outcome in all patients.

Is there a vaccine for TB?
Bacille Calmette-Guerin vaccine currently is the only vaccine available for TB. Although this vaccine is not widely used in the United States or Northern Europe, WHO recommends that BCG be given to infants and young children in countries where TB is common. The BCG vaccine does not always protect people from TB, and it should not be given during pregnancy or to children with symptomatic HIV infection.

Although BCG appears to reduce the risk of serious childhood forms of TB, BCG does not seem to be highly effective as people move into adulthood. Efforts to develop a more effective TB vaccine are underway, and researchers hope to make such a vaccine available within a decade.

What is multidrug-resistant TB?
The TB bacteria can become resistant to a drug or several drugs used to treat the disease. Drug resistance can occur when TB patients do not adhere to their prescribed drug regimens, health professionals prescribe an incorrect treatment regimen, or an unreliable drug supply interrupts patients' treatment. This means that the drug can no longer kill the bacteria.

Drug resistance is more common in people who have spent time with someone with drug-resistant TB disease; do not take their medicine regularly; do not take all of their prescribed medicine; develop TB disease after having taken TB medicine in the past; or come from areas where drug-resistant TB is common.

Sometimes the bacteria become resistant to more than one drug. This is called multidrug-resistant TB, or MDR-TB. People with MDR-TB disease must be treated with specific drugs that often are much more expensive than conventional therapy. These drugs are not as effective as the usual drugs for TB and they might cause more side effects. In addition, some people with MDR-TB disease must see a TB expert who can closely observe their treatment to ensure it is effective.

People who have spent time with someone with MDR-TB disease can become infected with TB bacteria that are resistant to several drugs. If they have a positive skin test reaction, they might be given preventive therapy. This is very important for people who are at high risk of developing MDR-TB disease, such as children and people living with HIV.

How does TB disease develop?
There are two possible ways a person can develop TB disease. The first applies to a person with latent TB infection -- when a person might have been infected with TB for years but has otherwise been healthy and without symptoms. However, it is possible for latent TB infection to become active at any time, particularly if a person's immune system is weakened. In this way, a person might become sick with TB disease months or even years after they first breathed the TB bacteria.

The other way TB disease develops happens much more quickly. Sometimes when a person first breathes in the TB bacteria the body is unable to protect itself against the disease. The bacteria then develop into active TB disease within weeks.

What is the TB skin test?
The TB skin test is one way to determine if a person has TB infection. Although there is more than one TB skin test, the preferred TB skin test is the Mantoux test, which also is called the PPD skin test.

For this test, a small amount of testing material is placed just below the top layers of skin, usually on the arm. Two to three days later, a health care worker checks the arm to see if a bump has developed and measures the size of the bump. If the bump is of a certain size then the person is presumed to have TB infection.

Because a TB skin test cannot distinguish between latent TB infection and active TB disease, a health care worker will want to determine if the person has active TB disease. This is done by using several other tests, including a chest X-ray and a test of a person's mucus coughed up from the lungs.

TB often is more difficult to diagnose in HIV-positive people than in HIV-negative people. The skin test might not be a reliable way to determine if people living with HIV/AIDS have TB. For HIV-positive people, chest X-rays and sputum cultures are recommended to determine if they have active TB. It also is recommended that HIV-positive people receive a skin test every six to 12 months, depending on their risk of coming into contact with TB bacteria.

What are the links between HIV and TB?
HIV/AIDS and TB are so closely connected that the terms "co-epidemic" or "dual epidemic" often are used to describe their relationship. The dual epidemic often is called TB/HIV or HIV/TB. HIV affects the immune system and increases the likelihood that people will acquire new TB infection. HIV also can facilitate both the progression of latent TB infection to active disease and relapse of the disease in previously treated patients. TB is one of the leading causes of death in HIV-positive people.

How many people are co-infected with TB and HIV?
An estimated 33% of the 40 million people living with HIV/AIDS worldwide are co-infected with TB. Furthermore, without proper treatment, approximately 90% of people living with HIV/AIDS die within months of contracting TB. The majority of people who are co-infected with both diseases live in sub-Saharan Africa.

What is the impact of co-infection with TB and HIV?
Each disease speeds up the progress of the other, and TB considerably shortens the survival time of people living with HIV/AIDS. TB kills up to half of all AIDS patients worldwide. People who are co-infected with HIV and TB are up to 50 times as likely to develop active TB in a given year as people who are HIV-negative.

HIV infection is the greatest risk factor for the progression of latent TB into active TB, and TB bacteria can accelerate the progress of HIV.

Many HIV-positive people in developing countries develop TB as the first sign of the later stages of the disease. The two diseases represent a deadly combination because they are more destructive together than either disease alone:

• TB is harder to diagnose in HIV-positive people.
• TB progresses faster in HIV-positive people.
• TB in HIV-positive people is almost certain to be fatal if undiagnosed or left untreated.
• TB occurs earlier in the course of HIV infection than many other opportunistic infections.

What is the impact of TB/HIV on women?
Women worldwide bear a disproportionate burden of poverty, poor health, malnutrition and disease. TB causes more deaths among women than all causes of maternal mortality combined, and more than 900 million women are infected with TB worldwide. This year, one million women will die and 2.5 million women -- mainly between the ages of 15 and 44 -- will become sick from the disease.

Once infected with TB, women of reproductive age are more susceptible to developing active TB than men of the same age. Women in this age group also are at greater risk of contracting HIV. As a result, in certain regions, young women ages 15 to 24 with TB outnumber young men of the same age with the disease.

While poverty is the underlying cause of many TB cases in rural areas, poverty also is aggravated by the impact of TB. In 1996, a study by the World Bank, World Health Organization and Harvard University reported TB was a leading cause of "healthy years lost" among women of reproductive age.

Source www.cdc.gov