According to the World Health Organization (WHO) there will be 10 million new cases of tuberculosis (TB) this year in the developing world. But the good news is that effective therapy will prevent the deaths of many of these patients. However, by the time the sick patients are diagnosed and treated, they will have infected many others in their community. Indeed, this 'failure of interruption' continues to keep the global epidemic of TB alive and well. Prompt diagnosis is thus key to treating and preventing the spread of TB.
Unfortunately, the techniques of TB diagnosis are antiquated. The most widely used method to test sputum ( 'khakar' in Nepali) for the TB bug is called the Ziehl-Neelsen stain, which is a 125-year-old technique. If TB was still prevalent in the Western world, there would surely have been major new breakthroughs in diagnostic techniques, but basically TB is a poor man's disease. So it was welcome news when a few days ago, WHO endorsed the GeneXpert device, a rapid test for TB, as "a major milestone for global tuberculosis diagnosis".
Unlike the Ziehl-Neelsen technique, GeneXpert does not need an expert to prepare a sputum slide and look for a bug under the microscope. This new molecular approach is more straightforward. After the patient spits into a cup, the sample is placed in an 'espresso' machine that examines the sample's DNA to see if it contains the genetic signature of TB. A simple, reliable 'yes' or 'no' answer is available in two hours. Importantly, GeneXpert can also determine within two hours if the bacteria is resistant to rifampicin, the most effective of the four-drug cocktail prescribed for TB. This allows treatment to account from the outset for resistant bacteria, and to tailor therapy accordingly.
However, the initial costs of about US$30,000 for the machine and at least US$20 for tests are daunting for the developing world. Unskilled workers can carry this test out with minimal training, but electricity is required. From hospitals in Bihar to the well-appointed Hinduja Hospital in Mumbai, great satisfaction has been expressed about the usefulness and accuracy of the device. But the cost continues to be an important issue, regardless of the scientific enormity of the breakthrough.