GeneXpert to be rolled out as first-line diagnostic for TB in South Africa

Theo Smart
Published: 31 March 2011

"If a minister can do it, it can’t be that hard," said South African Health Minister Aaron Motsoaledi, demonstrating the new GeneXpert test for TB (photo: Lettie Ferreira).

One of the most striking actions announced by Minister Motsoaledi during last week's launch of South Africa's new direction on TB control was the roll out of the GeneXpert MDR/RIF test for TB to become the first-line test to diagnose active TB throughout South Africa.

This self-contained TB diagnosis system automates sample processing on sputum providing real time PCR results. It promises to revolutionise the field by diagnosing both TB and rifampicin-resistance in under two hours (even in most smear-negative cases) — potentially a ‘while you wait’ test, so that a person could be tested, diagnosed and started on treatment on the same day.

In addition, since the test also detects the presence of rifampicin resistance, which generally indicates MDR-TB, people who present to care with MDR-TB could receive a diagnosis and be put onto effective treatment months earlier than under the current protocols.

Another major selling point is that the GeneXpert doesn’t require a sophisticated laboratory set-up or a highly trained lab technician to run this test — nurses or other staff could be trained to perform the test. In fact, at the start of the day, the Minister himself demonstrated performance of the test in front of the media, noting that 54 people had been trained in the previous two weeks to perform the GeneXpert test in South Africa — 55 including himself.

“If a minister can do it, it can’t be that hard,” he said, smiling for the cameras.

Perhaps even more striking, the test the Minister ran was not performed on the small desktop unit that has been piloted at several sites in South Africa. Instead, Prince Mshiyeni Hospital has been outfitted with the new ‘Infinity G-48’ machine, which performs 48 tests at a time, or approaching 200 on an 8-hour shift. This machine, which costs 2.8 million Rand (over US $400,000) is the only such machine in Africa, and one of only five such machines outside of the United States. Meanwhile, one G-16 machine (at 600,000 Rand each) has been placed in each of South Africa’s 9 provinces, and 20 G-4’s (which cost around 120,000 Rand each) have been placed in various sites across the country.

“Over the next 18 months, we will roll this out to the length and breadth of the whole country; we will put them in the national health laboratory services facilities,” said the Minister.

However, whether a country with such a huge burden of TB can truly scale up the capacity to switch TB diagnosis entirely over to GeneXpert systems in such a short time remains to be seen, and what it will actually cost is anyone’s guess. In addition to the equipment cost, the cost of each TB test is approximately $16 per test (for the reagent, not including the operator time). At present, South Africa performs about 4.6 million smear microscopy tests to diagnose somewhere over 400,000 TB cases each year. Accordingly, the Treatment Action Campaign continued to call for price reductions from the manufacturer in its World TB Day statement.

Presumably, fewer GeneXpert tests will be required than the two or three smears needed to diagnose TB because of their higher sensitivity — only one test would be required for each person being tested for TB, unless smear-negative TB is suspected.

According to Romain Prieur, Senior Manager for Tuberculosis at Cepheid, the company that makes GeneXpert, the test is only 75% sensitive in people with smear-negative TB, a second test increases sensitivity by about 10%, a third test, by another 5%.

Although the Department of Health (DOH) only plans one test per person, a second test may be warranted to reach 85% sensitivity in populations at greater risk of smear negative TB — such as people with HIV or children. But such operational issues are sure to be worked out as GeneXpert is increasingly used in clinical practice.

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