Tuberculosis (TB) kills two million people and infects nine million every year, and those numbers are rising, especially in southern Africa, which has the highest rates of HIV. TB-HIV co-infection is already a major problem and it is only getting worse, in part because of a lack of effective diagnostic tools and treatments. Dr. Peter Saranchuk was the medical coordinator at MSF’s HIV/AIDS project in Lesotho. Here, he explains the reasons behind the dangerous relationship between TB and HIV.

Why are so many people affected by HIV also affected by TB?

HIV slowly makes a person’s immune system weak over time, so they suffer from more infections, and these infections get more and more serious as time goes on. If a person is exposed to someone with TB in their household, everyone in that household is exposed. Normally, TB stays dormant inside the body, but if that person gets sick, and their immune system gets weak, then the TB germ starts to grow and cause active disease. So if it’s TB of the lungs (pulmonary TB), they start to cough, sweat at night, have a high temperature, lose their appetite, and lose weight, and this person with active TB slowly gets sick over time.

Does TB take a different course throughout the bodies of people infected with HIV than the bodies of healthy individuals?

Yes. And the reason is that the immune system is weaker and the body produces less sputum. When an HIV-positive person coughs, they only cough up a few TB germs in their sputum, and since people are tested for TB through sputum samples it’s very difficult to diagnose TB in an HIV-positive person. So, when this person coughs, they provide a sputum sample to the lab; it gets processed in the lab; the lab tech looks under a microscope at the slide; and, even though the person has TB, they’re not coughing up enough TB germs for it to be detected under a microscope. That’s what we call “smear-negative” TB, and the vast majority of people with pulmonary TB are smear-negative, so the traditional test for TB using the microscope really doesn’t help us much these days. That also means it’s very difficult to diagnose people with TB, and more importantly, the diagnosis is delayed, so they end up getting sicker and sicker and the TB symptoms get worse and worse, and often they have to get admitted to hospital in order to get the TB diagnosed. There are other ways to diagnose the TB

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