Patient delays in perceiving the symptoms of tuberculosis and the confounding fact that close to 50 % of the people who are tested positive for TB through sputum culture do not have the typical symptoms of the disease are complicating early diagnosis and treatment of TB in the State.
Subclinical or asymptomatic TB is thus emerging as a significant challenge when Kerala is said to be traversing the last mile towards TB elimination.
The National TB Prevalence survey (2019-21) had reported that the TB diagnosis of 42.6% of survey participants would have been missed if chest X ray had not been an additional screening tool. Because while their sputum culture was positive, they did not exhibit the typical symptoms of tuberculosis -- cough, chest pain, fever, night sweats, or weight loss.
“This means that there is a high probability that testing for TB only among those reporting with symptoms could result in our missing half of the pulmonary TB cases. Chest X-ray should be roped in as an important modality to screen for TB wherein the persons may have no symptoms suggestive of TB. All cases where Xray abnormalities are reported should be followed by a confirmatory molecular diagnostic test (NAAT), “ says P.S. Rakesh, senior Technical Advisor, International Union Against TB and Lung Diseases, Southeast Asia
The NTBP survey finding has now been reiterated by two recent global studies.
In a recent meta-analysis involving survey studies across Africa and Asia, the Amsterdam Institute for Global Health and Development reported that 82.8% of participants with TB reported no persistent cough and 62.5% reported no cough at all. About 29.1% of those without persistent cough and 23.1% of those with no cough at all had tested sputum culture-positive -- meaning that they were infectious and thus contributing to TB transmission.
In the recent issue of Lancet Journal of Infectious Diseases, Stuck, et.al , who conducted a meta analysis of surveys in countries with high incidence of TB between 2007-2020 reported that 27.7% of participants with tuberculosis had absolutely no symptoms of TB .
“There is no official figure for the proportion of asymptomatic/ subclinical TB in Kerala . But after the NTBP survey, I had interviewed all 17 TB cases detected from Kerala and 10 of them had no typical symptoms of TB,” says Dr. Rakesh. If people do not have symptoms, it is highly unlikely that they would seek medical care, thus eluding early TB diagnosis, while actively contributing to transmission
Chest X-rays should be an integral part of the initial screening of patients vulnerable to developing TB and should be used in conjunction with other confirmatory tests like NAAT. While Xray imaging cannot provide a definitive diagnosis of TB, it can show some typical features of the disease such as infiltrates or cavitation on the lungs.
However, accessibility to X-ray facilities has forever remained a challenge in Kerala as these are only available in taluk hospitals or above. Even in urban areas, people are unlikely to go to hospitals for a screening, especially if they do not have any symptoms.
NTBP survey had reported that in Kerala, 46% of those survey participants with symptoms had not approached the healthcare system either because they did not recognise their symptoms as that of TB or because they ignored it.
The answer lies in the introduction of portable or hand-held X-ray machines with AI technology so that people can be screened at primary health centres or in their own homes. These are battery-operated machines which weigh less than 3 kg and can produce over 100 images a day. A pilot feasibility study of these hand-held Xray machines in Wayanad last year had proved to be extremely useful in screening people living in difficult terrains.
Kerala has already done vulnerability mapping and Xray screening should be used amongst those identified as highly vulnerable -- contacts of active TB cases, the elderly, those who are undernourished, COPD patients and amongst the inmates in elderly care homes -- to detect cases
This is an investment that the State will have to make as subclinical TB poses a significant challenge to the goal of TB elimination. The integration of Xray screening into the diagnostic algorithm can benefit the State’s SWAS programme for respiratory health also.
