India is currently home to about more than 1.2 billion people among whom 2.2 million people develop the disease. According to numbers presented by WHO, almost 40 percent of the Indian population is infected with TB bacteria but only about 20 percent have the active form of the disease. Hence the other people who have the latent form of the disease become carriers of the same. Almost 0.5 million people succumb to this easily treatable disease each year. among the affected, 75 percent of the patients are in the economically productive age group which means every death can be associated with the loss of economic output in our country. To make the matters worse, the co-infection of HIV patients with TB is extremely common in a third world country like ours. On one hand the HIV cases are on the rise, 2.1 million currently live with the retroviral disease and on the other hand about 1.5 million of them are co-infected with multiple strains of the TB bacteria.
Why is TB diagnosis so difficult even in 2016?
The bacteria causing TB, Mycobacterium tuberculosis was discovered in 1882 by Robert Koch. With almost 150 years in hand for studying an isolated microbe one would think that diagnosis of such a prevalent disease would be a walk in the park. But in reality we mostly forget to factor in other facts.
Most of the TB tests especially the ones which use bacterial cultures and micro colony detection on solid media, take a long time (7-14 days). In addition to that, the sample collection methods in our country aren’t as efficient.
Chest x-rays have full potential to give a false negative result since it cannot exclude extra pulmonary TB.
Skin tests are a widely accepted method for testing for TB pathogens, but the test takes a long time as the patient must return after 48-72 hours for a healthcare professional to check his or her arm where tuberculin was injected. False negative as well as false positive results are not uncommon in people of countries which have high incidences of the disease (and hence most people are vaccinated with BCG).
Serological tests were usually recommended for their low turnaround time. Blood has a number of cells and proteins including the proteins produced by the infecting pathogens. In this case, the serological tests are used to detect the presence of Mycobacterium in the sample blood. However most of the market-ready serodiagnostic tools are known for their notoriously false-positive results. Hence the government has banned the import and use of such serological tests for the diagnosis of TB in India since 2012.
As we mentioned before, most HIV patients are co-infected with TB. However many of them do not show the classical symptoms of the disease, many of them produce clear chest/lung x-rays and even when detected some of them have sub-clinical form of the disease which is not technically treated with the same vigor. The diagnostic tools are not as fast as the progression of the disease in such patients who have all the chances of succumbing to the disease in less than a couple of months.
Many HIV infected individuals who also suffer from TB show false negative results on the sputum smear tests. The lack of advanced direct methods which is both fast and cost effective makes it extremely difficult in these cases for the detection of the disease.
To end it all, even in this era there is a stigma associated with the disease. Even with the multiple ad campaigns, awareness crusades and promising cures people are blinded by superstition and fear. This stops thousands of people from coming forward and receiving proper diagnosis and medication during the right time.
What are we doing about the problems in diagnosis?
Interferon Gamma Release Assay (IGRA): the Interferon Gamma Release Assay is used for the detection of the presence of TB bacteria in a whole blood sample. Although this test does not distinguish between the active and the latent form of the disease, this test usually takes 24 hours or less and does not produce false positives or false negatives. The only disadvantage being its cost and the limiting processing time after blood collection.
Automated microarray and PCR techniques: this is a milieu of multiple DNA techniques which takes relatively less time as compared to its older counterparts. The use the present trace amounts of pathogen DNA in sample blood as agents for further amplification during the diagnostic procedure. This also allows for an easy detection of the Rifampicin resistance gene, if present in the infecting strain.
Colorimetric reduction-oxidation indicator techniques: this is a fairly new tool which is endorsed by WHO; the colorimetric redox technique method is based on the reduction reaction of the indicator solution added to liquid culture medium. The change of color is indicative of resistance to different antibiotics including Rifampicin and Isoniazid. This test has about 95 percent sensitivity and also shows efficient MDR-TB (Multi-Drug Resistant TB) detection. This offers a cost-effective and fast method for the detection of TB among the current population of our country.
LED Fluorescence microscopy: smear techniques have been in practice for ages for the detection of TB. Coupling a popular practice like smear tests with LED microscopy techniques greatly increases the reach of the tests as well as their effectively. These LED microscopes allow a considerably larger area for smearing and hence allows a rapid and accurate examination of the samples at hand.
Line probe assays: the Line Probe Assays or LPAs are meticulous tests for diagnosing TB which was approved by WHO in 2008. This test has a whopping 98 percent sensitivity and 99 percent specificity for Rifampicin resistance. Hence if a person is positive for LPA a doctor can start treating him for MDR-TB while waiting for Drug Susceptibility Testing or DST reports to arrive. Rifampicin resistance can be used as a surrogate marker for MDR-TB.
New solid culture methods:
Nitrate Reduction Assay: new culture methods like the nitrate reduction assay can be used to detect the presence of Rifampicin and Isoniazid resistant forms of the bacteria in the isolated sample. This is actually a comparatively less expensive form of a liquid culture which can be used as a replacement for traditional DST studies for drug resistance tests.
Thin Layer Agar Culture: this technique requires nothing more than a standard microscope to detect the presence of TB pathogens as well as to detect Isoniazid and Rifampicin resistance. This test is a little time consuming as sample is collected and plated on alternate days for the first two weeks and then the process becomes less frequent. It takes about 7 days to confirm the status of infection and about 10-15 days for a complete DST report. However this is a really inexpensive procedure as it uses a combination of agar and light microscopy for the efficient detection of TB bacteria in sample.
Other new tools which are expected to be in the market soon-
There are several other diagnostic tools which are still in their early phase of development. A few of these tools and techniques include the following:
The breathalyzer screening test: much similar to the tools detecting the presence of alcohol in our breath, this one is designed to detect the presence of TB pathogens. This portable instrument can be run on AA batteries and is a beacon of hope for the high risk communities of our country,
Lipoarabinomannan (LAM) detection in urine: research shows that LAM is secreted in the urines of patients with active forms of the disease. Urine specimen is more easily collected as compared to sputum and blood. Also the qualitative tests performed are simple and cost effective. This allows visual amplification of the signals.
Phage Based Tests: this is a new age technology which employs bacteria eating phages (viruses). This can detect the presence of Rifampicin resistance and employs visual detection techniques.
TB Patch Test: this is point-of-care tests which are being developed to diagnose TB in a given population. The patch delivers a protein MPT64 which is highly specific for the TB pathogens. For those with active forms of the microbe a vesiculation or erythema forms within 3-4 days of the application of the patch.
Sodium Hypochlorite or Bleach microscopy: this is nothing but digestion of sputum with bleach prior to microscopy. This improves the yield even in high HIV-positive settings. This simple and promising process has been complicated by the lack of standardization and heterogeneity of sample collected.
What are the challenges faced during diagnosis in India?
A few obvious questions still loom; why is TB rarely detected on time in India? Why do most patients go untreated for the early developmental stages of the diseases?
The answers to those are not simple. It is a combination of socio-economic factors which delay the diagnosis as well as the treatment of (in most cases) a very treatable disease. In India resources are not easily available in rural areas; in combination with illiteracy and poor economic health this takes a huge toll on the diagnostics and treatment of TB in our country.
As discussed before almost 0.3 percent (2 million) of the population lives with HIV and this makes it even more difficult for the detection of the disease. Co-infection of HIV with TB makes it notoriously difficult to detect the presence of the latter. Most people who have both the ailments often pass away within weeks of infection without a chance of diagnosis or treatment.
The major challenges include poor healthcare infrastructure in mostly the rural areas, corrupt administration and uneven distribution of resources. The unregulated use of antibiotics against TB bacteria leads to widespread rise of MDR and XDR TB.
Even today people think that TB is a poor man’s disease. Hence the rich people who hire these so called poor people as their cooks, drivers and maids refuse to acknowledge the fact that they are equally susceptible to the disease which may be nestled in their employees asymptomatically. The denial and the lack of proper knowledge of the disease make it impossible to detect the disease in time even in the affluent classes, although there are sufficient resources.