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© Brendan Bannon |
“What we need is a simple test that tells you when you have active TB, which yields results almost instantly and can be used by any nurse or health worker even when far away from a laboratory…until we have a simple reliable test, many TB patients will keep falling through the net and die untreated.”
--Dr. Francis Varaine, MSF TB Coordinator.
Present TB diagnostic methods leave half of all patients undiagnosed
The most widely used technique for diagnosing active tuberculosis is sputum smear microscopy: a person suspected to have TB produces a sputum sample, coughed up from their lungs, that is examined under a microscope for evidence of TB mycobacteria.
While this method is cheap and easy enough to use in all but the most remote areas, it is not a very sensitive test and detects less than half of all active TB cases. In addition, people with extra-pulmonary TB (infection outside the lungs) and children go undetected by this method.
As a result, people can be given the wrong treatment that not only puts their own lives at risk but also allows the TB mycobacteria to develop resistance to the drugs. Such drug-resistant strains, in turn, pose a grave threat to others who could contract them. More sophisticated and sensitive techniques exist for diagnosing TB, but they aren’t suitable for use in the settings where most people with TB live and where MSF works.
“Only 7% of the limited funding available for TB research and development is spent on diagnostics. Most of the tests under development will not be simple enough to use in resource-limited settings and will not reliably detect the disease. Finding a more reliable but simple test to detect TB and rapid tests to detect drug resistance must be global priorities for health research.”
-- Dr. Tido von Schoen-Angerer, executive director, Campaign for Access to Essential Medicines.
Drug-resistant strains and HIV co-infection multiply challenges
Testing for TB with a microscope can at best only reveal whether the TB mycobacteria are present or not in the sputum of a patient. In the case of people with drug-resistant TB, further tests are necessary to pinpoint the particular resistant strain infecting the patient. This can only be carried out at present by growing the bacilla in a well-equipped laboratory. The bacilla then have to be tested to find out which drugs they are resistant to again in laboratory conditions. Drug resistance can be more rapidly detected by new molecular tests but these again requre excellent laboratory conditions. These kinds of diagnostic tests just can’t be done in the remote areas where MSF works. The length of time it takes to get the results through means many patients don’t get the correct treatment in time. In the case of XDR-TB, most patients will die before they can be correctly diagnosed. Diagnosing people who are HIV positive is also extremely difficult because there are less bacteria in their sputum and the disease is more prevalent outside the lungs in these cases. The result is that many patients going undiagnosed and die.
What needs to happen:
To read full report TB diagnosis and Drug Sensitivity Testing 
UPDATE: In January 2009, WHO produced a preliminary document that described 19 new or improved diagnostic tools of the many that are being explored. Three of the tools described in the document have already been endorsed by WHO and are being implemented by countries, while the others are still under development or in piloting phase and are expected to be ready for review for appropriateness for scaled-up use in the coming years. A finalised pipeline is expected later.
Click here to link to the WHO document
Learn more about Tuberculosis
