New TB treatment promises to cut infection rates

AP

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It has been 30 years since SA altered the tuberculosis treatment guidelines. However, a recent change holds the promise of curing more drug-resistant (DR) TB cases and a reduction in infections.

To the a non-specialist, the detail is technical, but in essence, the arrival of rapid TB diagnostics now allows health workers to arrive at an effective treatment path within a day or two of taking a sputum sample, as opposed to weeks.

The old guidelines (used by health workers to guide their work) before the arrival of the, among others, Gene Xpert diagnosis machine, dictated that patients suspected of having DR TB had to wait between six and eight weeks for the diagnosis to be confirmed, often exposed unnecessarily to antiquated, painful and toxic drug regimens.

Others were put on standard TB treatment, which would have no effect in combating the DR TB strain – this in turn meant the patient remained infectious, possibly passing the virus to relatives, friends and others in close proximity. Those who were particularly ill would often die while waiting.

Until recently, the vast majority of patients who were diagnosed with TB were treated for the standard TB strain until the diagnosis of drug resistance was made.

Those suspected of having DR TB – in come cases referred to at “retreatment cases” – were placed on an altered treatment plan (Regimen 2), including a painful injectable streptomycin, administered only at a health institution.

The guideline change has in the main been brought about with the rollout of new, rapid and highly effective diagnostic tools – the Gene Xpert machine and the Line Probe Assay (LPA).

The Gene Xpert is a machine that can detect TB in a sample of sputum.

This technique is called PCR (polymerase chain reaction), and allows the machine to also look at the structure of the genes. This is important to detect if a TB bacterium has developed resistance to drugs.

The DNA of the TB bacterium is, in a way, like a long string of different colours. If one or more of the colours change (if there is a mutation in the DNA), then the bacterium can become resistant to certain TB drugs.

The Gene Xpert can test for resistance to one of the most common TB drugs, rifampicin. This means that it can tell two things: first, whether a person has TB, and second, whether the TB that the person has can be treated with rifampicin.

Absence

Rather than relying on visualising bacteria under a microscope, the LPA indirectly detects the presence of TB, also relying on a PCR process.

Amplified material can subsequently be seen on a strip by the presence or absence of bands, much like a pregnancy test. LPA also detects resistance to rifampicin.

Before, it would take between six and eight weeks for a DR TB diagnosis to be made, as the bacteria had to be cultivated in a laboratory.

Now, with the rollout of the Gene Xpert Technology, the diagnosis of DR TB can be confirmed within 24 to 48 hours.

This means that Regimen 2, which includes streptomycin, is now being phased out.

Streptomycin is the oldest TB drug, and in some cases causes hearing and balance loss as well as some kidney problems.

“When the diagnosis of TB is made, we know with certainty if the patient has drug- sensitive or -resistant TB.

“Right from the outset, the correct medication will be prescribed,” explained Dr Francesca Conradie, the clinical adviser on TB for Right to Care. – Health e-News