4 September 2012

South Africa: Important Change to TB Guidelines

It has been 30 years since South Africa altered the Tuberculosis (TB) 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) pre-arrival of the among others the GeneXpert 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 family, friends and other who are 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 suspect of having DR TB, in come cases referred to at "retreatment cases" were immediately placed on an altered treatment plan (Regimen 2), which included a painful injectable streptomycin, only administered at a health institution.

This group of patients, termed 'retreatment cases', are individuals who have taken four or more weeks of TB treatment and are now smear or culture positive or have been clinically diagnosed with TB, in other words they are suspected to have DR TB, but this still needs to confirmed with a test.

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.

The sputum is placed in a disposable cartridge, which is fed into the machine.

The machine looks for the DNA specific to the TB bacterium. If there are TB bacteria in the sample, the machine will detect their DNA and automatically multiply it. 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 or not a person has TB, and second, whether or not the TB that the person has can be treated with rifampicin.

Rather than relying on visualizing bacteria under a microscope, the LPA indirectly detects 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 GeneXpert 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 Conradie, clinical advisor for TB for Right to Care.

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