A new study by a combined team of researchers from the Queensland University of Technology and The University of Queensland (UQ) has found that bacteria from coughs and sneezes can spread up to 4 meters and remain alive in the air for 45 minutes.

Professor Lidia Morawska, the lead author of the study and the Director of the International Laboratory for Air Quality and Health, says the study is one of the first to study the longevity of airborne pseudomonas aeruginosa bacteria when they are expelled by human coughs and sneezes. Pseudomonas aeruginosa is the most common type of multi-drug resistant pathogen that can cause infections in humans with weakened immune systems when they are in hospital.

“Our previous research had found that these pathogens travelled up to 4m and stayed viable for 45 minutes after being coughed into the air,” says Morawska in a statement. “We wanted to find out how far bacteria-carrying droplets expelled by sneezes or coughs travel such distances and remain able to infect other people after such a long time. Most research in this area to date has focussed on laboratory-generated bio-aerosols, or airborne droplets, which are different from natural respiratory droplets generated by humans in composition and mechanisms of production.”

For the study, the team developed a technique known as Tandem Aged Respiratory Droplet Investigation System (TARDIS) to target the short-term and long-term ageing of bio-aerosols from people, without contamination from the ambient air. To demonstrate the technique, they sampled airborne cough droplets from two patients with cystic fibrosis and chronic pseudomonas aeruginosa infection. They found that the bacteria in the cough droplets from the patients decayed in two different time spans.

Researchers also found that shortly after the cough droplets hit the air, they dried out, cooled and became light enough to stay airborne. They also gradually degrade through contact with oxygen in the air, with larger droplets taking much longer to evaporate. Moreover, the concentration of active bacteria in the dried droplets showed rapid decay with a 10-second half-life for most of the bacteria but a subset of bacteria had a half-life of more than 10 minutes. Researchers say this happens because some of the pseudomonas aeruginosa bacteria are “resistant to rapid biological decay and thus remain viable in room air long enough to form an airborne infection risk, especially to people with respiratory problems such as patients with cystic fibrosis.”

“We think this could be because droplets are produced in different parts of the respiratory tract and carry different ‘loads’ of bacteria,” says Morawska. “The larger droplets carrying bacteria take longer to evaporate which makes them more resistant to decay and able to maintain bacteria viability for extended periods.”

Researcher believe they could find the new treatment for infections and treatment of people with cystic fibrosis with their new findings.

Source/Reference: QUT | A Novel Method and Its Application to Measuring Pathogen Decay in Bioaerosols from Patients with Respiratory Disease. PLOS ONE, 2017. DOI: 10.1371/journal.pone.0158763