Subclinical tuberculosis throws up challenges for State’s TB elimination drive

Patient delays in perceiving the symptoms of tuberculosis (TB) 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 (201921) had reported that the TB diagnosis of 42.6% of the survey participants would have been missed if chest Xray had not been an additional screening tool.

No typical symptoms

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 Xray 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 Adviser, International Union Against TB and Lung Diseases, Southeast Asia.

Two global studies

The NTBP survey finding has now been reiterated by two recent global studies.

In a recent metaanalysis 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 the Lancet Journal of Infectious Diseases, Stuck, et.al, who conducted a metaanalysis of surveys in countries with high incidence of TB between 2007 and 2020 reported that 27.7% of the 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.

Chest Xrays 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.

It can show some typical features of the disease such as infiltrates or cavitation on the lungs. However, Xray facilities are only available in taluk hospitals or above.

The 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.

Portable machines

The answer lies in the introduction of portable or handheld Xray machines with artificial intelligence technology so that people can be screened at primary health centres or in their own homes. These are batteryoperated machines which weigh less than 3 kg and can produce over 100 images a day.

A pilot feasibility study of these handheld Xray machines in Wayanad last year had proved to be extremely useful in screening people living in difficult terrains.

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.