Tuberculosis, sometimes referred to as TB, is a disease caused by an organism called mycobacterium tuberculosis. The mycobacterium tuberculosis bacteria can attack any part of the body, but most commonly attack the lungs.
A person can have active or inactive (sometimes called latent) tuberculosis. Active tuberculosis or TB disease means the bacteria are active in the body and the immune system is unable to stop them from causing illness. People with active tuberculosis in their lungs can pass the bacteria on to anyone they come into close contact with. When a person with active tuberculosis coughs, sneezes or spits, people nearby may breathe in the tuberculosis bacteria and become infected.
People can also be infected with tuberculosis bacteria that are not active in their body. If a person has latent tuberculosis, it means their body has been able to successfully fight the TB bacteria and stop them from causing illness. People who have latent tuberculosis do not feel sick, do not have symptoms and cannot pass tuberculosis on to other people. In some people tuberculosis bacteria remain inactive for a lifetime without becoming active. But in some other people the inactive tuberculosis may become active tuberculosis if the person's immune system becomes weakened - for example by HIV.
The symptoms of tuberculosis depend on where in the body the TB bacteria are growing. Tuberculosis bacteria often grow in the lungs, causing pulmonary tuberculosis. Pulmonary tuberculosis may cause a bad cough that lasts longer than three weeks, pain in the chest and coughing up of blood or sputum. Other symptoms of TB disease include weakness or fatigue, weight loss, lack of appetite, chills, fever and night sweats.
Inactive or latent tuberculosis has no symptoms.
Tuberculosis can be diagnosed by injecting a small amount of fluid called tuberculin into the skin of someone's arm. If the skin reacts by swelling then the person is probably infected with tuberculosis. However, this method is not wholly reliable at detecting TB infections among HIV-infected people because their weakened immune systems often cannot mount a strong enough defence against the injected proteins to cause swelling. It also detects both active and latent tuberculosis, meaning the test is not very accurate at diagnosing active TB disease in people who live in areas where tuberculosis (and thus latent TB infection) is very common.
Diagnosis of tuberculosis in the lungs may be made using an X-ray or sputum test, but again, these may not give a clear indication of active TB infection in HIV positive people, because their immune systems are not strong enough to mount an inflammatory reaction against the bacteria. In cases of extra-pulmonary tuberculosis (where the disease is affecting organs other than the lungs), fluid or tissue samples may be tested.
If there is doubt about the diagnosis of tuberculosis, a culture of TB bacteria can also be grown in a laboratory. However, this requires specialised and costly equipment and can take six to eight weeks to produce a result.
If the necessary facilities are unavailable then the tuberculosis diagnosis is often based on symptoms.
Active tuberculosis disease can almost always be cured with a combination of antibiotics. The variety of treatments and drug options depend on the country you are in. A proper combination of anti-tuberculosis drugs provides both prevention and cure. Effective treatment quickly makes the person with tuberculosis non-contagious and therefore prevents further spread of tuberculosis. Achieving a cure for TB takes about six to eight months of daily treatment.
Several drugs are needed to treat active tuberculosis. Taking several drugs does a better job of killing all of the bacteria and is more likely to prevent them from becoming resistant to the drugs. The most common drugs are:
To ensure thorough treatment, it is often recommended that the patient takes his or her pills in the presence of someone who can supervise the therapy. This approach is called DOTS (directly observed treatment, short course). DOTS cures tuberculosis in 95% of cases.
There is a vaccine against tuberculosis called BCG, but the vaccine is now very old (it was first used in the 1920s), and tests have found it to be very variable in its ability to protect people from infection in modern settings. When it does provide protection form tuberuclosis, this generally only lasts for around 15 years. The BCG can also cause false-positive readings on the tuberculin skin test. If given to HIV positive adults or children with very weak immune systems, the BCG can occasionally cause disseminated BCG disease, which is often fatal.
A drug called isoniazid (INH) can be used as a preventative therapy for those who are at high risk of becoming infected with tuberculosis or for those who have inactive TB. People who have inactive tuberculosis but are not yet sick can take a course of isoniazid for several months to stop them developing active tuberculosis.
The WHO recommends that HIV positive people who have latent tuberculosis (but definitely not active TB) should be offered isoniazid preventive therapy as needed.
When a strain of tuberculosis bacteria is resistant to two or more 'first-line' antibiotic drugs it is called multi-drug resistant TB or MDR-TB. When it is resistant to three or more 'second-line' antibiotics as well, it is classed as extreme drug resistant tuberculosis, or XDR-TB. Drug resistance usually arises when tuberculosis patients do not or cannot take their medicine as prescribed, and drug-resistant mutations of the bacteria are allowed to replicate. People can also catch MDR and XDR-TB from others.
MDR-TB is a serious problem and is very difficult to treat. In normal treatment (sometimes referred to as 'first-line' treatment) for tuberculosis, patients take the drugs isoniazid and rifampicin (the most effective tuberculosis drug available) plus other drugs for around six to eight months. If a person is resistant to isoniazid and rifampicin however, they are said to have MDR-TB, and will need to change to a regime containing newer and often less widely-available 'second-line' drugs. Treatment with second-line drugs can take a very long time, and is usually far more expensive than standard DOTS therapy because most of the drugs are still under patent.
XDR-TB is even more serious. If someone has XDR-TB, it means they are not only resistant to isoniazid and rifampicin, but to three or more of the six available second-line drugs too. This can make it virtually impossible to formulate an effective treatment regime for them. Many people with XDR-TB will die before it is even realised that they have the extreme resistant strain.
In 2006, 53 people in the province of KwaZulu Natal in South Africa were identified as having XDR-TB. Of these people, 52 died within 25 days of tuberculosis being diagnosed. The majority were HIV positive. However, progress is being made to better understand XDR-TB globally. In South Africa, by late 2006 an estimated 2000 - 3000 people with XDR-TB, and a similar or higher number of people with MDR-TB were on treatment with second-line drugs.
Although HIV infection does not of itself increase the chance of drug resistance occurring, both MDR-TB and XDR-TB are very serious threats to HIV positive people, whose weakened immune systems render them unlikely to fight off tuberculosis naturally (often the only hope for those with a resistant strain).
Of the people who worldwide died of tuberculosis in 2009, it is estimated that 400,000 were infected with HIV. Tuberculosis is the leading cause of death among HIV infected people in Africa.
It is estimated that one third of the 34 million people living with HIV/AIDS worldwide are co-infected with TB.
Because tuberculosis can spread through the air, the increase in active tuberculosis among people infected with both tuberculosis and HIV results in:
People with latent tuberculosis are increasingly becoming infected with HIV, and many more are developing active TB because HIV is weakening their immune system. People who are co-infected with both HIV and latent TB have an up to 50 times greater risk of developing active tuberculosis disease and becoming infectious compared to people not infected with HIV.
People with advanced HIV infection are vulnerable to a wide range of infections and malignancies that are called 'opportunistic infections' because they take advantage of the opportunity offered by a weakened immune system. Tuberculosis is an HIV related opportunistic infection. A person that has both HIV and active tuberculosis has an AIDS defining illness.
The HIV/AIDS epidemic is reviving an old problem in well resourced countries and greatly worsening the existing problem of tuberculosis in resource poor countries. There are several important associations between the epidemics of HIV and tuberculosis:
It is vitally important for people with HIV to have treatment if they have active tuberculosis. This will cure them of TB and prevent transmission to others. Even in settings where antiretroviral drugs are unavailable or inaccessible, it is crucial that the health system is able to offer HIV positive people the simple drugs needed for DOTS.
For some people it can be difficult to take drugs for both tuberculosis and HIV at the same time. Some anti-HIV drugs can also interact with some tuberculosis drugs making the treatment more difficult. It is important that the tuberculosis treatment is taken regularly and exactly as the health care provider has advised. If the drugs are not taken regularly, the bacteria can become resistant to the drugs and this can be dangerous.
As one of the first opportunistic infections to appear in HIV-infected people, tuberculosis may be one of the earlier signs of HIV infection. Addressing tuberculosis offers the opportunity for early HIV intervention. Although treatment of tuberculosis can improve the quality of life of HIV positive people and prolong their life, it cannot stop them from dying of AIDS. This is why access to antiretroviral treatment is also vitally important.
Around the world, attempts are being made to improve collaboration between tuberculosis and HIV programmes. It is being proposed that everyone diagnosed with tuberculosis should be tested for HIV and vice-versa, and that treatment programmes should share facilities and expertise.
The importance of tuberculosis to the global HIV epidemic is enormous. Tuberculosis is a serious health problem in its own right but it is also the most likely cause of death for HIV positive people. Like HIV, tuberculosis has had an uneven impact around the world. In some parts of the world, tuberculosis is increasing after almost forty years of decline. Escalating tuberculosis rates over the past decade in many countries in sub-Saharan Africa and in parts of South-East Asia are mainly due to the HIV epidemic.
Between 1990 and 2005, tuberculosis incidence rates tripled in African countries with high HIV prevalence. In 2007, Africa accounted for an estimated 78% of tuberculosis cases among HIV-positive people worldwide.
The largest number of tuberculosis cases occurs in Asia, which in 2009 accounted for an estimated 56% of the global total. However the estimated incidence per capita in sub-Saharan Africa is around twice that of South-East Asia.