The
airborne transmission of diseases including the common cold, influenza and
tuberculosis is something that affects everyone with an average sneeze or cough
sending around 100,000 contagious germs into the air at speeds of up to 100
miles per hour.
New
research led by scientists from the University of Bristol and published
today in the Journal of the Royal Society Interface, outlines a new technique
that, for the first time, examines directly the environmental factors that
control the transmission of disease to the level of a single aerosol particle
and a single bacterium.
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 the differences in airborne transmission of
the virus is not well understood.
To
help understand this process better, scientists have established a novel
approach for forming aerosol droplets containing a specific number of bacteria,
trapping a cloud of these droplets of exact known population and simulating
their environmental exposure over a time from five seconds to several days.
The
study reports on the benchmarking of this new approach, demonstrating the many
advantages over conventional techniques, which include introducing large
populations of droplets to large rotating drums or capturing droplets on
spiders' webs.
Not
only can measurements be made down to the single bacterium/single droplet level
requiring very little quantity of aerosol (picolitres), but high time
resolution (one second) measurements of viability can be made, allowing the
first quantitative studies of the influence of dynamic factors transforming the
aerosol (for example evaporation, condensation) on viability.
For
example, the study shows that during evaporation of droplets, the concentration
of typical salts can rise way beyond their solubility limit, placing
considerable osmotic stress on the bacteria and reducing viability.
Posted by Dr. Tim Sandle, Pharmaceutical Microbiology
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