While persistent cough has been a hallmark symptom of tuberculosis, there should be new ways identified to diagnose the world's most deadly infection as a new study on 13 March showed a majority of the patients do not have the common symptom.

The study, published in the journal Lancet Infectious Diseases, analysed data on more than 600,000 individuals in Africa and Asia.

The results showed that 82.8 per cent of people with tuberculosis had no persistent cough and 62.5 per cent had no cough at all.

The infection is predominantly transmitted by coughing, but probably also through simply breathing, said researchers from the Amsterdam University Medical Center (UMC) in the Netherlands.

"Our results indicate the probable reason why, despite huge efforts to diagnose and treat the disease, the tuberculosis burden across Africa and Asia is hardly declining. We already knew that there was a giant gap between the 10.6 million who got ill with tuberculosis and the 7.5 million cases that were registered by health authorities in 2022," said Frank Cobelens, Professor of Global Health at Amsterdam UMC.

"A persistent cough is often the entry point for a diagnosis, but if 80 per cent of those with TB do not have one, then it means that a diagnosis will happen later, possibly after the infection has already been transmitted to many others, or not at all,” he added.

Further, the analysis of national monitoring schemes in 12 countries showed similar results.

While the majority lacked cough, more than a quarter of those with TB had no symptoms at all -- these were seen more in women than men.

Also, a quarter of the patients without cough showed high loads of bacteria in their sputum and were probably highly infectious.

"When we take all of these factors into account, it becomes clear that we need to rethink large aspects of how we identify people with TB. It is clear that current practice, especially in the most resource-poor settings will miss large numbers of patients with TB. We should instead focus on X-ray screening and the development of new inexpensive and easy-to-use tests" Cobelens said.