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Tuberculosis (TB) is an infection of the lungs and respiratory system. Along with HIV, TB is one of the world's leading causes of death due to disease. The Centers for Disease Control and Prevention (CDC) reports that, in 2010, close to nine million people became sick with TB and over 1.4 million died from TB worldwide. In the US, the number of new TB cases each year has been going down for eighteen straight years. However, there are still 10-15 million people in the US who are infected with TB.
TB is caused by a bacterium called Mycobacterium tuberculosis. It spreads from person to person when an infected person coughs, sneezes, laughs, or spits. Tiny droplets of fluid from the lungs are carried in the air and can be breathed in by someone nearby. Although it can affect many parts of the body, TB usually occurs in the lungs.
Not everyone who is infected with TB bacteria develops "active" disease.
People with weakened immune systems are more likely to develop active TB disease. This includes people living with HIV (HIV+), children, elderly people, and people who take drugs that suppress the immune system. Research shows that people living with HIV are at least ten times more likely to develop active TB disease than HIV-negative people. You can develop active TB with any CD4 count. Studies also show that TB can worsen HIV disease progression. Having active TB disease while HIV+ is an AIDS-defining condition.
Worldwide, TB is the leading cause of death in HIV+ people. The US government recommends that you be screened every year for TB if you are HIV+ by having a skin or blood test (see "Diagnosing TB," below).
TB is spread through the air when an infected person coughs, sneezes or spits. It usually takes a long time for TB transmission to occur. Family members of people with TB, people living in the same house, health-care workers, and people who live in residential facilities like homeless shelters and prisons are most likely to get TB. People with latent (not active) TB do not spread the disease. Once a person with active TB starts treatment (see "TB Treatment" below), they usually cannot spread the disease after 2-3 weeks on treatment.
People with active TB should be separated from others until they can no longer spread the disease. If you have TB or spend time around people with TB, wear a disposable face mask. Certain types of air filters can trap the TB bacteria, and ultraviolet light can kill it.
After TB bacteria are inhaled, they settle in the lungs. People with healthy immune systems can usually fight the bacteria and keep it from multiplying. The immune system may build structures that wall off the bacteria. These structures can burst, leaving scars in the lungs. If a person's immune system is too weak and the structures burst, the bacteria can get out and enter the bloodstream. Once in the bloodstream they travel to other parts of the body including the brain, kidneys, and bones. This is called "extrapulmonary TB." Extrapulmonary TB is more likely in people with advanced HIV disease.
People with active TB disease may develop symptoms including:
It is recommended that HIV+ people get screened for TB once a year using a skin or blood test. The skin test is called a TST (tuberculin skin test) or PPD (purified protein derivative). A small amount of "tuberculin" (a TB protein) is injected under the skin of the arm, and the test is "read" 2-3 days later, by a health care worker who looks at the spot on the arm and measures any swelling. The test is positive if the area develops a hard swelling under the skin that is bigger than 5mm.
There is also a TB blood test, called an IGRA (interferon-gamma release assay), which measures your immune response to TB. Because HIV+ people sometimes do not develop a positive TB skin test reaction even if they are infected, the TB blood test is now the preferred test for those living with HIV. An added benefit to the IGRA test is that there is no need to return to a health clinic; results are usually available within 24 hours and can be communicated by phone.
A positive TB skin or blood test shows that you have been exposed to TB, but it does not mean you have active TB disease. Your health care provider will look at your symptoms as well as other tests, such as chest X-rays and sputum tests, before diagnosing you with active TB disease.
There are two types of treatment for TB:
HIV+ people who have latent or inactive TB can be treated with TB drugs to prevent them from developing active disease. The usual treatment includes taking an antibiotic called isoniazid (INH) with pyridoxine (vitamin B6) once or twice weekly for nine months. However, the CDC now also recommends a combination of INH and rifapentine taken once a week for 12 weeks while directly observed. With directly observed therapy (DOT), a nurse, outreach worker, or family member watches the person with TB take her or his pills each week. The 12 week DOT regimen is NOT recommended for HIV+ people taking antiretroviral therapy. Your health care provider will help you decide which treatment option is best for you.
Treatment of active TB requires combination therapy. The usual regimen is:
These four drugs are taken daily for two months. Tests can be done to see how well the drugs are fighting the TB. If the drugs are fighting the TB well, treatment changes to just isoniazid plus rifampin for four more months.
TB drugs can cause some side effects. For example, isoniazid can cause nerve damage (peripheral neuropathy) or liver damage, and ethambutol can cause vision problems. It is important not to drink alcohol while taking isoniazid, or you can badly damage your liver. Pyridoxine (vitamin B6) may be given with INH to prevent nerve damage from this drug.
Some TB drugs can interact with HIV drugs. Rifampin, for example, can interfere with protease inhibitors and non-nucleoside reverse transcriptase inhibitors. This can make it difficult to treat both diseases at the same time. If you are taking a protease inhibitor, your health care provider may make changes to your TB drugs. Your provider may also adjust your drug doses when you are being treated for both TB and HIV. Some HIV+ people may need longer TB treatment than people without HIV.
As with HIV, taking your TB drugs exactly as prescribed (good adherence) is very important. The full course of treatment must be completed, even if you feel better before you have finished taking all your drugs (symptoms usually improve after 3-4 weeks). This helps prevent TB from coming back and becoming resistant to drugs.
Like HIV, TB can change to become resistant to drugs, especially if a drug is used alone. This can cause the drugs to stop working. Therefore, it is important for your provider to test your TB for drug resistance. Drug-resistant tuberculosis (DR TB) must be treated with a combination of drugs. Some TB strains are now resistant to several different drugs. These strains are called multiple-drug resistant tuberculosis (MDR TB) and extensively-drug resistant tuberculosis (XDR TB). XDR TB is resistant to almost all medications used to treat TB. As a result, many more people with XDR TB die or have treatment failure.
According to the CDC, untreated TB is a greater threat to pregnant women and their babies than TB treatment. Therefore, it is important to screen for and treat TB in pregnant women. Both the TB skin test and the TB blood test are safe during pregnancy. As with anyone who is not pregnant, additional tests are needed to determine if someone who tests positive for TB with a skin or blood test has active TB disease.
For pregnant women with latent or inactive TB, INH taken once or twice weekly for 9 months is the usual treatment. It is important for pregnant women taking INH to take pyridoxine (vitamin B6) to help prevent nerve damage. The 12-week regimen of INH plus rifapentine is NOT currently recommended for women who are pregnant or who expect to become pregnant in the next 3 months.
In pregnant women with active TB disease, the usual treatment is INH, rifampin, and ethambutol daily for 2 months followed by INH plus rifampin for 7 months (for a total of 9 months of treatment). Pregnant women should not take streptomycin because it can cause deafness in babies. Pyrazinamide is most often not recommended during pregnancy, as its effects on the developing baby are not yet known. Other TB drugs that should be avoided during pregnancy include: kanamycin, amikacin, capreomycin, and fluoroquinolones (an entire group or type of antibiotics).
TB is a serious disease that is the leading cause of death in HIV+ people worldwide. Many people can keep TB under control and have latent, or inactive, disease. But people with weakened immune systems, including HIV+ people, are much more likely to develop active TB disease that needs treatment. In many ways, TB and HIV treatment are similar. Both diseases must be treated with a combination of drugs, since using only one drug can lead to resistance. With both TB and HIV, good adherence is an important factor in successful treatment. But unlike HIV, TB can usually be completely cured after less than a year of treatment.