Portable Air Sampler Detects Airborne TB DNA in South African Clinics

A study published in Open Forum Infectious Diseases reports that a small, electrostatic air-sampling device can detect aerosolized Mycobacterium tuberculosis (Mtb) DNA directly from patients’ coughs in routine clinical settings. The findings suggest that this portable approach may one day complement or even replace sputum-based tuberculosis (TB) testing—particularly for patients unable to produce sputum or with subclinical disease.

Researchers from Stellenbosch University and the Karolinska Institutet evaluated the TB Hotspot Detector (THOR), a 400-gram electrostatic sampler that quietly collects charged airborne particles onto a steel rod for DNA testing using Xpert MTB/RIF Ultra. The study enrolled 178 adults with pulmonary TB symptoms from primary health clinics in Cape Town between April and December 2024, ultimately analyzing 137 participants whose environmental control samples were negative.

THOR detected Mtb DNA in nearly half of participants (47%), with sensitivity and specificity of 46.6% and 76.5%, respectively, when compared with sputum Ultra results. Sensitivity rose to about 57% among those with high bacterial loads, and strikingly, Mtb DNA was also found in 24% of participants whose sputum tested negative.

Male sex and higher sputum bacterial load were strongly associated with positive aerosol detection. Men with moderate-to-high sputum Mtb levels had more than three times the risk of aerosolized DNA detection compared with women or men with lower bacillary loads. Conversely, participants reporting fever were less likely to yield positive aerosol samples—a finding the authors speculate may reflect weaker cough strength during acute illness.

Despite stringent decontamination, Mtb DNA was also found in about 30% of environmental samples taken before participant testing, underscoring both THOR’s sampling power and the persistent airborne transmission risks in TB-endemic clinics.

The study highlights THOR’s practicality compared with traditional research-grade systems like the Cough Aerosol Sampling System (CASS) and the Respiratory Aerosol Sampling Chamber (RASC), which require bulky equipment and specialized facilities. While earlier CASS and RASC studies have reported Mtb aerosol detection rates ranging from 25% to 90%, those experiments were typically conducted under highly controlled laboratory conditions. THOR, by contrast, functioned silently within small clinic booths powered by portable batteries—mimicking real exposure settings.

The authors note, however, that DNA detection does not necessarily confirm viable bacteria. Yet in high-burden, untreated populations, the presence of Mtb DNA likely serves as a reasonable proxy for infectiousness. The device could therefore be valuable for identifying “super-spreaders”—individuals who release unusually high quantities of infectious aerosols—and for monitoring airborne TB contamination in healthcare environments.