Closing in on Airborne TB

We were very fortunate to have Professor Robin Wood and Dr Keren Middelkoop, both from the Desmond Tutu HIV Centre (DTHC), update us on the tuberculosis (TB) aerosol project. The project aims to characterise how airborne TB infects people in different spaces. South Africa is one of the six countries globally with the highest rates of TB, where the bacteria is responsible for the highest percentage of deaths among HIV-positive South Africans. Identifying high-risk spaces for TB infection and improving diagnosis will help eradicate the disease.

The Latest in Aerosol Capture

Robin Wood and Keren Middelkoop May research meeting | Caroline Reid

Wood summarised the progress made in measuring individual airborne TB bacteria. For this latest research by DTHC, each patient spent a short amount of time in an air-controlled kiosk. Clean air is pumped in, breathed by the patient, and captured. The team then analyse the air to see how the composition of the air has changed. For example, the carbon dioxide (CO2) levels should be higher due to exhalation. Each participant had TB, yet the kiosk identified just over 40% of participants as having TB. This result is useful, but indicates that less infectious cases of TB will be missed.

Measuring airborne bacteria, like tuberculosis, is tricky because the number of bacteria in a large quantity of air might be very small. As a result, the team has been aiming to develop more sensitive gadgets that are less likely to miss organisms. The new device will allow the team to measure the exhaled breath directly, instead of collecting it in the kiosk. Wood believes this will improve the sensitivity of exhaled air measurements, as high airflow capture increases the chance of capturing individual TB bacterium and other organisms.

Airborne TB in Communal Spaces

Middelkoop presented a different component of the same project. She has been sampling air in communal spaces to see if TB bacteria is in the atmosphere. As Wood explained, this is tricky and the project is currently in the ‘proof of concept’ stage. They assess the particles in the air by using a filter over a vacuum that traps these small particles, including TB. If successful, this process has the potential to identify areas with a high risk of TB transmission and thus advise on how to reduce the risk.

The team has completed over 70 air samples. Empty, windy fields with low amounts of TB were used to create negative controls. Low rates of TB were found in TB-controlled environments, such as the medical clinics where measures (such as opening doors and windows) have been put in place to reduce TB transmission.

TB levels in the air were higher in places where levels of CO2 (rebreathed air) were also high. When many people share a poorly-ventilated space, the CO2 levels increase because everyone rebreathes the same air. Eventually, the team wants to go to communal spaces (such as churches, schools, etc) and use this technique to evaluate the TB levels quickly and reliably. This is helpful because if a space is shown to have no TB, then testing for TB becomes a low priority. However, if the filter finds TB, then everyone can be tested and treated quickly before the bacteria spreads.

At the moment, identifying cases of TB in the community is expensive and time-consuming. Doctors knock on every door and test everyone. This new method provides the potential to screen many people at a time, and nip new cases in the bud before they infect more people.

We wish Wood and Middelkoop the best of luck as they continue their valuable project, and thank them for an engaging presentation.


Written by Caroline Reid