New technique for identifying TB DNA in exhaled air

Scientists have developed a new device that may help identify tuberculosis DNA from exhaled air -- known as aerosols.

Tuberculosis is an airborne disease that is often diagnosed by analysing sputum -- mucus coughed up from the lungs. However, not all patients are able to produce sputum, which makes detection more difficult.

Researchers at Karolinska Institutet in Sweden tested whether DNA from the tuberculosis bacterium could be detected in exhaled air.

"It is promising that we can detect infectious tuberculosis directly in the air, especially in settings where sputum samples are difficult to obtain," said Jay Achar, researcher in the Department of Global Public Health at Karolinska Institutet.

The study, published in Open Forum Infectious Diseases, was conducted at primary care clinics in South Africa and included 137 adult participants with tuberculosis.

The team used a new device, TB Hotspot detectOR (THOR), which collects aerosols using electrostatic sampling. The samples were analysed using the same technique as for sputum, Xpert MTB/RIF Ultra.

The results show that the method was able to detect tuberculosis DNA in exhaled air in 47 per cent of those who had a positive sputum test.

Among those with high levels of bacteria in sputum, the sensitivity was slightly higher at 57 per cent.

At the same time, the specificity -- the ability to correctly identify those without the disease -- was 77 per cent.

The study also found that certain factors increased the likelihood of detecting tuberculosis DNA in aerosols. This was particularly true for men with high bacterial levels in sputum. Conversely, people with fever were slightly less likely to test positive in air samples.

"This is a first step towards understanding how tuberculosis is transmitted and how we can identify infectious individuals earlier," Achar said.