Assessment of aerial survival of bacteria in aerosol droplets from coughing and sneezing

Airborne transmission of diseases such as colds, flu and tuberculosis is a problem that affects all people with sneezing or coughing, who send about 100,000 infectious germs in the air at a maximum speed of 100 miles to the hour.

New research conducted by scientists from the University of Bristol and published today in the Journal of the Royal Society Interface, describes a new technique that, for the first time, directly examines the environmental factors that control the transmission of disease at the level of a single aerosol particle and a single bacterium.

Aerosol droplets are a typical means of transporting pathogens, such as bacteria and viruses, and transmitting diseases by air.

The impact of environmental factors (such as relative humidity, temperature, atmospheric oxidants and the presence of light) on the viability and infectivity of pathogens in aerosol droplets remains poorly understood.

For example, although the seasonal variation in influenza cases is known, the environmental factors determining differences in virus transmission by air are not well understood.

To help better understand this process, scientists have developed a new approach to form aerosol droplets containing a specific number of bacteria, trapping a cloud of exactly known population droplets and simulating their environmental exposure on a period from five seconds to several days.

The aerosol droplets are then gently sampled on a surface to determine the number of bacteria surviving the aerosol phase.

The study presents the comparative badysis of this new approach, demonstrating the many advantages over conventional techniques, including the introduction of large populations of droplets into large rotating drums or the capture of droplets on spider webs.

One can not only perform measurements up to the single bacterium / at the level of a single drop requiring very little aerosol (picoliters), but it is also possible to perform measurements of viability with a high temporal resolution (one second), thus allowing to realize the first quantitative studies of the influence of dynamics. factors transforming the aerosol (eg, evaporation, condensation) on viability.

For example, the study shows that during droplet evaporation, the concentration of typical salts can greatly exceed the solubility limit, which imposes considerable osmotic stress on the bacteria and reduces their viability.

Lead author Professor Jonathan Reid of Bristol University School of Chemistry said, "This new technique offers the potential prospect of allowing more precise measurements to improve our understanding of the transmission of many transmitted diseases. by air, including tuberculosis, influenza virus and foot and mouth disease. "

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