Tuberculosis is one of the leading causes of death in people with HIV, resulting in an estimated13 percent of AIDS deaths worldwide.  As Véronique LaCapra reports, doctors working with the World Health Organization stress the need to coordinate the response to these two catastrophic epidemics, and to integrate TB screening and treatment into HIV care. 

An x-ray of a patient affected by tuberculosis

More than 2 billion people – one third of the world's population – are infected with tuberculosis bacilli, the bacteria that cause TB. The disease disproportionately affects the world's poor: the vast majority of TB deaths are in developing countries.

In the general population, 1 in 10 people who are infected with TB will develop the disease in their lifetime. But for people who are HIV-positive, TB presents a much greater risk.

Doctor Diane Havlir is the Chief of the HIV/AIDS Division at San Francisco General Hospital in California. She is active in the World Health Organization's efforts to combat HIV and TB, and has been studying the relationship between these global epidemics. "It's estimated that just over a third of all the people living with HIV – which means over 10 million people – are infected with tuberculosis." She says that in patients who have HIV disease, TB is the leading cause of death.

Countries suffering the highest incidence of HIV and AIDS bear much of the burden: according to WHO, 85 percent of HIV-positive TB cases are in Africa.

Tuberculosis can be difficult to diagnose, says Havlir, especially in developing countries, which often have limited diagnostic tools. She says that in most places in the world, tuberculosis is still diagnosed using a practice that was developed over a hundred years ago: microscopic examination of sputum.

But using a microscope to look for TB bacteria in the thick mucus people cough up from their lungs often doesn't work. According to Havlir, only about 50 percent of people infected with both TB and HIV will have enough tuberculosis bacilli in their sputum to be visible under a microscope. "That really makes the diagnosis challenging."

It's also challenging to recognize the symptoms of tuberculosis in someone with HIV. An otherwise healthy person who gets sick from TB usually develops pneumonia-like symptoms – coughing, fever, chest pains, and sweats.

But in people with weak immune systems, like AIDS patients, TB can spread throughout the body, entering lymph nodes, causing glands to swell, and producing severe abdominal pain. Tuberculosis can also spread to the brain, resulting in headaches and seizures.

Havlir proposes that to effectively fight the spread of tuberculosis, HIV programs must make TB control a priority.

She says the first step is to increase routine testing for TB in HIV clinics. Since tuberculosis is highly contagious – spreading through the air when someone with TB coughs, sneezes or even talks – early diagnosis is critical to preventing an infected person from spreading the disease to others. "The sooner that we find people, the sooner we can treat people, and the less […] time that they are able to transmit tuberculosis to others," Havlir explains. Family members are especially at risk, as are other patients in a health care facility. Havlir says that just having people with TB wear a simple paper mask over their mouths can help prevent transmission.

Testing for TB can also provide direct benefits to the person getting tested, even if the results are negative. For an HIV-positive person who does not have TB, says Havlir, taking a single antibiotic – called isoniazid – may reduce their risk of getting TB in the future by up to 60 percent.

"Another tool that we have in order to prevent the risk for tuberculosis in our HIV-infected patients is HIV therapy itself," says Havlir. One of the reasons that people with HIV are so susceptible to TB is that the HIV virus impairs their immune system. Taking anti-retroviral medications strengthens the immune system, decreasing susceptibility to infection.

Havlir discusses these and other strategies to coordinate TB and HIV control in the July 23rd issue of the Journal of the American Medical Association.