DURBAN] Clinical trials of a new molecular technique have found it to be effective at quickly identifying multidrug-resistant tuberculosis (MDR-TB) in resource-poor settings.
As a result, the WHO has endorsed the use of the test in all countries with MDR-TB.
South Africa's National Health Laboratory Service and Medical Research Council (MRC), and the Foundation for Innovative Diagnostics (FIND) collaborated to test 30,000 patients suspected to have MDR-TB in South Africa between 2007 and 2008. They used both the rapid test and conventional testing.
They announced the results at the opening of the 2008 South African Tuberculosis conference in Durban this week (1 July).
The test uses polymerase chain reaction (PCR) technology to amplify Mycobacterium tuberculosis DNA and look for genetic mutations that cause resistance to drugs.
It is the first of its kind to be used against TB and the first new tool for TB in 50 years, says Martie van der Walt, acting director of the TB Epidemiology and Intervention Research Unit at the MRC.
The new TB test yielded results on 92 per cent of all samples compared with about three-quarters (77.5 per cent) of samples tested by conventional methods. It takes between eight hours and two days to get a result, compared to six to eight weeks for conventional testing.
Patients who receive appropriate drugs sooner minimise their risk of acquiring additional drug resistance, van der Walt told SciDev.Net. Earlier diagnosis also cuts the chance of infecting others.
Seventeen countries will receive the tests over the next four years through the WHO Stop TB Partnership's Global Drug Facility. FIND and the WHO's Global Laboratory Initiative will help countries build the capacity — such as laboratory equipment and trained staff — to carry out tests based on PCR techniques.
"Information" from StopTB.org
However it is clear that this initiative goes only so far in meeting the medical needs. In addition, several further issues are also of concern:
The tests are problematic for ‘smear negative’ TB patients
The new diagnostic method is based on the DNA analysis of resistant mycobacterium tuberculosis in sputum samples. But many TB patients are either unable to produce sputum or are sputum negative and the WHO does not recommend this new technology for use in smear negative patients. This is problematic in that for instance up to 50% of TB patients co- infected with HIV are sputum negative. Similarly patient suffering from extra pulmonary TB will not produce TB bacterium in their sputum. Since in some places, up to 80% of TB patients are co-infected with HIV, this means the test will be of restricted use in high burden HIV countries.
The test will not be available in the most peripheral settings
The new testing method can only be processed in well equipped laboratory conditions, requiring at least three different rooms, constant power supply, refrigeration facilities and very well trained staff – unavailable in the remotest settings. This kind of testing can only be carried out in laboratories at a regional level. This means that many of those with TB cannot be reached through implementation of the new tests.
The test is still expensive
At present, the cost of testing for MDR TB stands at around 34USD. The new test, after training and equipment costs are included, is offered at 20 USD which is still far too high for most health systems and individuals in developing countries. At present the tests are offered at this price only to South Africa and unless things change, this leaves the remaining 15 countries with a much larger bill. Price reductions must be made available across the board for all countries wishing to use this new technology
Still need for culture and drug-sensitivity testing
Another drawback to the test is that while it can rapidly give a yes-no answer as to whether the patient is multi-drug resistant or not, it cannot give more detailed information on the drug resistance status of the patient. To be able to exclude extremely drug resistant TB (XDR TB), which would require further adaptation to the already complex and toxic MDR-TB-treatment, culture techniques and performance of DST have still to be in place.
Furthermore, culture must still be employed in order to follow-up on patients and monitor whether they are responding to treatment as the new technique cannot give the answer whether the bacilli detected are still alive or not.
Therefore, the new technique may be able to reduce the numbers of cultures performed but it cannot replace it, which will also have an impact on the total costs for the health system.
Laboratory failings are not the key factor
WHO and its partners suggest that it is mainly the lack of laboratory capacity that is responsible for the enrollment of only 2 % of patients in need for effective MDR-TB care. As explained above, this is certainly not the single most important obstacle: Highly complex treatment regimens, lack of effective 2nd line drugs, trained staff and infrastructure, diagnostic and treatment costs that are still far too high - these are just some additional examples why effective MDR-TB care is still severely restricted
Need for many and varied fronts in battle against TB
The medical needs for tackling drug resistant TB are many and urgent. TB is a public health emergency and demands a multi-faceted, co-ordinated response on many fronts including ramping up overall funding for TB drugs and diagnostic research, stimulating trials and pushing on drug development.
While these new testing methods/techniques should be welcomed as a useful additional weapon in our battle against TB, with its limitations, it can only remain one part of the solution.
*The iniatives have been launched by WHO, the Stop TB Partnership, UNITAID and the Foundation for Innovative New Diagnostics (FIND).