Tuberculosis bacteria found in 90% of symptomatic individuals not officially diagnosed with TB

Mycobacterium tuberculosis (Mtb), the bacterium responsible for tuberculosis infections, is detectable in the exhaled breath of 90% of individuals with suspected tuberculosis, including those who tested negative on conventional sputum tests and were not diagnosed with TB. This suggests a potential risk of transmission among those who have tested negative.

Researchers from the University of Cape Town and Amsterdam UMC analyzed data from over 100 patients who sought treatment at clinics in South Africa. These findings are published in the journal PNAS.

If someone carries Mtb in their respiratory tract, this may also mean they can spread it. Therefore, since these results suggest a much broader range of people transmitting TB than previously recognized, there are significant implications for public health interventions designed to interrupt transmission.”

Ben Patterson, External Ph.D. Candidate, Amsterdam University Medical Center

Ben Patterson is also associated with the Amsterdam Institute for Global Health and Development.

The study’s participants saw two community clinics in Cape Town’s southwest before receiving a TB diagnosis or not. After that, aerosol samples were gathered utilizing a novel technique designed to locate low concentrations of Mtb in a community-based dedicated TB aerobiology lab.

After that, the presence of Mtb was discovered in the samples provided by 90% of the patients, even those whose sputum tests for tuberculosis had come back negative. 

This rather shatters the paradigm on the transmission of tuberculosis. Previously we understood that Mtb was only expelled by those who have the disease, but this study shows that also those with symptoms who test negative do this and probably spread the infection.”

Frank Cobelens, Professor, Global Health, Amsterdam University Medical Center

Frank Cobelens is a Senior Fellow at the AIGHD.

For a period of six months, each participant underwent three separate aerosol samplings. Remarkably, during this time, Mtb was less prevalent in both the treatment-treated and non-treated groups. However, after six months, 20% of all participants still tested positive for Mtb in aerosol.

This implies that transmission can go on for longer than previously believed. In fact, a recent study by researchers at the University of Cape Town indicates that tuberculosis may exist in the lungs for as long as four years before symptoms appear. 

Together, our results indicate how complex tuberculosis is, and perhaps also why it is so difficult to eliminate tuberculosis in endemic areas. Even when public health agencies work, according to the current guidelines, effectively against symptomatic TB cases. In this sense, a revaluation of our practices is necessary.”

Frank Cobelens, Professor, Global Health, Amsterdam University Medical Center