The arrival of the colder temperatures of autumn also signals the return of the flu season. A new study shows that this season can however take place in very different ways depending on whether one lives in a big city or a smaller urban center.
The flu virus is one of the most unpredictable we know about. Several factors play a role in the transmission of the virus, such as variations in the type of strain itself, the level of contact between two people, the effectiveness of their immune system or the degree of humidity in the air.
The work of a team of American scientists has just shown that the size of cities also has a role to play in the progression of infections.
Their results suggest that less densely populated areas are at greatest risk for intense, short-lived influenza seasons, while larger cities may end up with much longer seasons.
The researchers made this observation by tracking health data from 603 cities across the United States between 2002 and 2008.
In cities with 100,000 inhabitants, the majority of infections occur over a short period of time, usually around a peak at a specific time during the winter.
For their part, the big cities of more than one million inhabitants lived a more diffuse season in the time. And while the total number of infections was higher for the whole season, not all infections occurred at the same time.
These results suggest that small towns are more likely to experience epidemics where a large percentage of the population will become infected during the same period, which may overload the local health network. Meanwhile, the big cities will experience a much longer season, but with fewer intense episodes.
Dry weather and proximity
The influenza virus is able to spread easily in the air. Its main mode of transmission is found in mucus or saliva transformed into an aerosol by sneezing or coughing.
It can then travel in the air for a short distance and end up on different surfaces waiting for human contact.
However, the amount of time he is able to spend outside the body without being destroyed varies greatly depending on the ambient temperature.
Studies have already shown that the virus could remain infectious out of the body for more than a day when the air was dry, like the one that accompanies colder temperatures. On the other hand, the virus seems to have difficulty spreading in wetter conditions.
When it’s in a large, densely populated urban center, the virus does not have to wait for the cold winter weather to start flowing. The proximity of people to each other allows the influenza season to begin at times when the temperature lends itself less and to extend.
On the other hand, in less populated areas, the virus will need conditions conducive to its spread to promote its chances of coming into contact with another person. It is for this reason that a larger percentage of the population will get sick on the arrival of cold, dry weather.
For researchers, these results show that strategies to counter the spread of influenza need to be adapted to population density, including methods to reduce contagion in large cities and better resources to cope with waves of influenza. infections in less populated areas.