It is a little late to get vaccinated
against the flu but
at least we can try to avoid it. Dodging the flu is probably
difficult than previously thought. Indeed, bypassing patients
who cough is probably not enough to avoid inhaling viral particles.
American researchers, whose
work has just been published in the advanced edition of the Proceedings of the US
National Academy of Sciences (Pnas)
add some valuable information to existing recommendations. They realized that even
without coughing, a sick person who breathes and speaks spreads the
virus around him.
The researchers asked 142
people to breathe normally for 30 minutes in a device that collected
air around them. The volunteers could of
course cough or sneeze, and they also had to recite the alphabet three
times during this half-hour.
The participants all had
influenza, confirmed by specimens, whose symptoms had appeared for one
to three days. This period corresponds to
that of maximum contagiousness in case of contamination.
To enter the study,
volunteers recruited from 355 students with signs of respiratory
infections had to have either a rapid diagnostic test (from a
nasopharyngeal sample) indicating flu, a temperature above 37.8 ° C,
with an irritated cough or throat.
Only one in three patients
have fever and muscle aches
The symptoms of the flu are
numerous. In a study conducted in
Hong Kong seven years ago, three-quarters of influenza patients had
signs of rhinitis (congested nose, runny nose), two-thirds coughed,
half had sore throats and headache and only one in three patients with
fever and muscle pain (myalgia).
Among the particles
expelled by cough, there are droplets of varying sizes. Three years ago, a team
from Massachusetts Institute of Technology (MIT) in Boston showed that
the cloud of droplets and gases that form when someone coughs can
spread widely. While it was thought that
the smallest droplets did not go beyond one meter, the MIT researchers
discovered that droplets could go up to six meters
away, carried by the
cloud! And as the warm moist air
rises and diffuses widely, a patient quickly contaminates the space
where he is confined.
The new Pnas study confirms
this potential for aerial dissemination of viral particles, since 39%
of aerosol samples (finest droplets, less than 5 micrometers) were
found in the virus, but most of them were collected in half of the
samples. the volunteers had neither coughed nor sneezed during the 30
minutes of the experiment. Researchers were
because usually the cough
carries the virus.
Another surprise, the
presence of virus in the nose has not, apparently, played a large role
in the aerial dissemination of viruses. "This is why," the
researchers write, "we can conclude that the airways of the head (nose,
throat, Ed) are only a small contribution to the production of
aerosolized viruses and that this comes from the 'lung infection.'
They also note that "women
tend to cough for a lower viral load than men". And cough more frequently
at equivalent viral load. "It could be that women
have a more sensitive cough reflex," they say.
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flu might be spread by breathing, speaking