On March 24th 1882, German physician and biologist, Dr Robert Koch announced to the world that he had discovered the agent that causes tuberculosis. He had managed to identify the bacteria through growing them in different growth media as well as examining specimens under a microscope. In the early to mid-1890s, bacteriologist Frank Ziehl and pathologist Friedrich Neelsen refined the technique used by Dr. Koch to what is now known as the Ziehl-Neelsen or ZN stain.
Fast forward to 2016 and the ZN staining technique is still the most commonly used and widely accessible method of diagnosing TB in low and middle-income countries. This includes Kenya, which has close to 1,900 laboratories that offer TB diagnosis using microscopy. The World Health Organization (WHO) recommends each country should have at least one microscopy centre per 100,000 population. Kenya has at least 4 microscopy centres for every 100,000 persons thus surpassing WHO recommendation and attaining national coverage with this simple and inexpensive diagnostic tool. While this is no mean achievement, it is important to note that the simple microscopy technique is not without flaws. Though specific to the genus Mycobaterium it does not distinguish between the causative agent for TB i.e. Mycobacterium tuberculosis and other Mycobaterium species which are commonly found in water and soil. Furthermore, microscopy does not differentiate between dead bacilli and those that are alive, it only detects between 40 and 60% of those infected. More importantly, the technique does not detect drug resistant TB, a form of the disease that does not respond to first line drugs.
Growth of M. tuberculosis though commonly practiced in developed countries is not as common in low and middle-income countries. Considered as the gold standard, Lowenstein-Jensen (LJ) was the most commonly used method for isolating the bacteria in the laboratory. Amongst the advantages that LJ has is its ability to detect between 30 – 50% more cases than microscopy, the ability to perform additional testing such as drug susceptibility testing to determine whether patients have drug resistant TB. Another culture method commonly employed is the Becton Dickinson (BD) Mycobacteria Growth Indicator Tube (MGIT) which in addition to the LJ advantages has even higher sensitivities as well as detects the bacteria faster than LJ. Culture techniques however require complex infrastructure, take long periods of time (up to 8 weeks), advanced training, have significantly higher infection risks to the laboratory personnel as well as higher costs compared to microscopy. Kenya has two public facilities as well as a few private facilities that perform cultures. WHO recommends at least one culture facility per 1 million population.
In an attempt to shorten the time to diagnosis and through continued research, the global TB fraternity has developed molecular techniques that drastically shorten the time to diagnosis. Polymerase Chain Reaction (PCR) techniques are based extraction of M. tuberculosis DNA, amplifying resistance determining regions of the gene from sputum specimens, and a process of hybridization then follows before detection through colorimetric development. There are two PCR methods available in Kenya namely Hain Lifescience’s Line Probe Assay (LPA) and Cepheid’s Xpert MTB/RIF. Endorsed by WHO in 2008, LPA requires three separate laboratory rooms in order to avoid contamination and has multiple steps once specimens are received at the laboratory and thus most often results are only available after two days of specimen submission. However, a big advantage that LPA has over microscopy is that it is highly sensitive and besides confirming the presence of M. tuberculosis in a specimen, it also detects resistance to the most potent anti-TB drugs i.e. Rifampicin and Isoniazid. It is also significantly faster than culture in time to diagnosis.
December 2010 saw the entry of Xpert MTB/RIF into the global TB diagnostic market after WHO’s endorsement of the technology for routine use. Co-developed by Cepheid Inc. and the Foundation for Innovative New Diagnostics (FIND), Xpert MTB/RIF is a real-time PCR technique that extracts, amplifies, detects and quantifies resistance-determining regions of the gene simultaneously. GeneXpert as it is commonly known, has revolutionized TB diagnosis in its simplicity compared to LPA as there are very minimal specimen manipulations by the technicians, its minimum infrastructure requirements, ability to detect TB and resistance to Rifampicin but most importantly, is the 100 minutes test result turn-round time. Kenya is considered one of the early implementers of Xpert MTB/RIF, and to date, all 47 counties in Kenya have at least one instrument. A total of 129 4-module machines have been installed and are operational. The instruments can perform a total of 16 tests per day and are estimated to have an annual capacity of 2,000 tests. This means that a total of 252,000 patients with symptoms of TB can be screened for TB and Rifampicin resistance every year. In 2015 alone Kenya tested up to 80,000 people on GeneXpert. Whereas Xpert has huge advantages over all other diagnostic methods, there are still some disadvantages such as the need for constant power, and inability to distinguish between dead TB bacteria and live ones.
The Ministry of Health has made major strides in the fight against TB as evidenced by the falling incidence and prevalence. However, it all starts with diagnosis and in the wise words of Martin H Fischer, “diagnosis is not the end but the beginning of practice.”
As we enter into the end TB era, Kenya will need to build on its successes and further strengthen linkages between diagnostics and treatment to ensure faster results and faster treatment initiation. The country also needs to look out for new and upcoming innovative technologies that could further increase access to drug resistance testing. The Xpert Omni has potential of being implemented at the lowest level of the health care setting and even be deployed through outreaches as they use rechargeable batteries. In line with Kenya’s 2016 World TB Day theme, “Mulika TB, Maliza TB” let us join together in raising awareness of this preventable, treatable and curable disease.
By Mr. Jesse Wambugu, a Technical Officer at the Foundation for Innovative New Diagnostics (FIND) and a TB laboratory expert.