Dr. Neha Lal, Consultant Microbiologist – National Reference Lab, Oncquest Laboratories Ltd, Gurugram
In order for India to completely eradicate tuberculosis, emphasis on timely diagnosis and adopting recent developments in diagnostics are extremely important
India has come a long way to combat tuberculosis. Mass media campaign to create awareness, ending the stigma and myths surrounding the disease and diagnostic facilities at the grassroots level are some of the factor that have helped India to achieve lower cases of tuberculosis year on year. Tuberculosis is one of the ten major causes of mortality worldwide. Therefore, timely diagnosis of TB is imperative to cure a person and prevent the infection from spreading.
Tuberculosis Screening- Then and Now
We also need to remember that not everyone infected with TB gets sick. Sometime the infection can be inactive and is called latent TB. When a person has latent TB, they don’t feel have any symptoms or feel sick but can spread the disease to others. Therefore, it is crucial to diagnose TB effectively and in early stages.
Doctors will check patients for possible TB symptoms. Before prescribing any tests, doctors will do a physical examination by checking the lymph nodes for swelling and use a stethoscope to listen to the sounds of the patient’s lungs make when they breathe. The diagnosis and treatment have evolved over the years. One of the early diagnostic tools that were developed in the first part of twentieth century is a TB skin test.
Clemens von Pirquet, an Australian scientist and pediatrician developed a skin test for tuberculosis diagnosis in 1907, where a small amount of tuberculin is put under the skin and the body’s reaction is measured. He also invented the term “latent TB infection” in 1909. In 1908, Charles Mantoux, a French physician, updated the skin test by using a needle and syringe to inject the tuberculin under the skin. American Florence Seibert, an American biochemist further developed the process to create a purified protein derivative of tuberculin (PPD) for the TB skin test. The US government adopted the technology after which the process became standardized.
There are majorly two types of TB tests that doctors prescribe for screening a patient: a TB skin test and a TB blood test.
The most commonly used diagnostic tool for tuberculosis is a skin test called Mantoux test, named after Charles Mantoux, a French physician. It is also called PPD test. In Mantoux test, a small amount of a substance called tuberculin is injected just below the skin on inside the forearm of the patient. After 48 to 72 hours, the injected arm is checked for swelling. The result is interpreted in terms of indurations across the forearm in millimeters. Indurations of anything above 5mm are considered to be positive while 0mm is considered negative.
If the test result is positive, then it is followed by a chest X-ray or a CT scan to see spots in the patient’s lungs or it might reveal changes in their lungs caused by active tuberculosis. However, Mantoux test is not always hundred percent accurate and can give false-positive result too.
Doctors and healthcare professionals today prefer blood test for screening TB. The tuberculosis blood test is also called an Interferon Gamma Release Assay or IGRA. There are two kinds of TB blood tests: Quanti FERON-TB and T-SPOT.TB. While blood tests are used for screening, it cannot determine if the patient has an active or a latent TB. Further diagnosis including chest X-ray or a CT scan help doctors to understand the nature of the infection better. Another diagnosis that is effective to test TB is sputum test which is one of the best ways to determine if the patient has an active TB infection or not. Sputum test is also helpful to determine if the treatment is working or not.
According to World Health Organization guidelies, all patients having signs and symptoms of Presumptive TB should be diagnosed with CB-NAAT as the initial diagnostic test. The CB-NAAT (Catridge based Nucleic Amplification test) test which is a rapid molecular test providing results within 2 hours, is now being made available throughout India.
There is also now the Truenat Test which is starting to be used. Conventional methods such as bacterial culture, identification of an M. tuberculosis complex and Drug Susceptibility Testing are slow and cumbersome, therefore, rapid DST using molecular technologies such as line probe assays is recommended over conventional testing nowadays.
The Road Ahead
The TB National Strategic Plan (NSP) 2020 – 2025 is the plan which sets out what the Government of India (GoI) now believes is needed to eliminate TB in India by 2025. The key interventions which are focused on reducing the incidence are Population screening for TB through outreach, Use of molecular tests for TB diagnosis, High standard of care in private sector through comprehensive engagement; Achieving a high rate of treatment success, and Introducing preventative therapy of adult and adolescent contacts. As a nation, we have to work together to end tuberculosis and the importance of timely diagnosis in this regard can’t be stressed enough. The government’s ambitious and bold plan to end TB by 2025 is a step ahead in the right direction. In India, to end tuberculosis completely, we need to take into account the perspectives and opinions of different stakeholders and must work coherently to tackle tuberculosis for the future generations.
