Tuberculosis ranks alongside HIV/AIDS as a leading cause of death worldwide. According to the World Health Organisation, 1.5 million people died from TB in 2014. The challenges in tackling the disease include the facts that people are tested too late and that the turnaround for most tests is long. To remedy this a point-of-care rapid diagnostic test for TB has been developed by a multinational team of scientists led by researchers at Stellenbosch University in South Africa. One of its co-inventors, Professor Gerhard Walzl, spoke to The Conversation Africa’s health and medicine editor Candice Bailey.
How have TB tests been done up until now and what are the challenges?
There are three main tests that are currently in use.
A culture test – the most sensitive – requires people to produce a sputum sample that is sent to a centralised laboratory where a culture test is done. A positive result shows up after ten days. A confirmed negative result takes up to 42 days.
The problem with this test is that it is only available in centralised laboratories, which means patients must make several trips to a hospital or health facility to get their results. And it is very expensive.
Then there is the sputum microscopy test. This is widely used in Africa. It requires the sputum slides of each patient to be individually checked.
The test is inexpensive. But it is labour intensive, which means that only a limited number of smear tests can be assessed a day. In addition, it only has a 60% sensitivity rate.
On top of this, the test poses particular challenges for children and for people living with HIV.
In the case of young children, samples need to be taken from their stomachs as they cannot follow instructions to produce a good quality sputum sample. This requires the use of a nasal tube, which is not pleasant for the child or the health-care worker.
The test also isn’t effective for people living with HIV. This is because their sputum often has low levels of the bacteria, which can lead to a false negative test result.
There is also a molecular test that detects bacterial DNA in the sputum sample. This test only takes two hours to produce a result and although it speeds up the detection of TB, it is not widely available to people in rural areas as instruments are placed in a centralised manner.
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