Colds and flu: why are more in winter?

The cold has a distant relationship with the cooling point in the "Swiss medical journal", doctors and Christian Daniel Genné Chuard.

While "viral respiratory infections, including influenza, occur mainly in winter in temperate zones", as well as bacterial infections superimposed pneumonia, the explanation for this observation factors are generally not intervene cold, remember the two Swiss doctors.

Although the exact cause of these seasonal fluctuations is not known, "environmental changes have been proposed to explain this situation," the authors explain.

"For example, a variation of the time of exposure to the light of day showed an increased susceptibility to pneumococcal infections in mice," they continue.

Other transitional changes may facilitate infections. Thus, "changes in the airway mucosa by viruses can alter the elimination of encapsulated bacteria" and a surface protein of the influenza virus "potentiates in vitro bacterial adherence to the mucosa," remind physicians .

However, none of these assumptions involves the cold as direct risk factor, they said. The most likely explanation for the surge in the number of colds and flu in winter hypothesis is ... the tendency to gather in places closed to keep warm, say the doctors.

Faced with the persistent belief that "catch a cold" can lead to these diseases, "a clear public information on the modes of transmission of respiratory viruses (aerosols and / or hand carriage) is essential, especially when it discuss in public the threat of a bird flu pandemic, "the authors conclude.