Although respiratory tract infections can occur throughout the year, the cold temperature and low humidity typical of autumn and winter favor them to occur more frequently at these times of the year. Since coronaviruses penetrate the respiratory system, it is reasonable for us to wonder if extreme cold will have an impact on the course of the pandemic.
Respiratory tract infections are the most common infections worldwide, responsible for 20% of excess winter mortality, as well as a considerable economic burden on public health. The incidence of the common cold varies by age, with the highest rates found in children under 5 years of age. They have three to eight viral respiratory illnesses per year, while adolescents and adults have about two to four, and those over 60 have an average of less than one. Despite these alarming numbers, keep in mind that most heal on their own and completely.
It is bacteria and viruses, not the weather, that cause these infections. So why do so many people get sick in the cold and wet fall and winter months? I point out some reasons that justify this connection and that depend on both human behavior and our physiology.
After the summer, the children go back to school. Close contact increases the chance that viruses and, less often, bacteria, will spread.
Cold weather causes more time to be spent indoors. This promotes close exposure to other people, who may be infected.
In addition, there are more factors related to air quality in closed environments, in homes or offices, where people spend more than 90% of their time.
The most common cold-causing viruses survive best in cold, low-humidity environments, such as fall and winter.
Inhalation of cold air, cooling of the body surface and cold stress provoke pathophysiological responses, such as the alteration of our immune system, which can contribute to an increased susceptibility to respiratory infections.
Vitamin D plays an important role in maintaining a healthy immune system. Reduced exposure to the sun during winter can lead to lower levels of vitamin D.
In studies with mice, it has been seen that, as we lower the temperature, they have reduced production of interferons, which is the intrinsic antiviral defense, which leads to the infection being more persistent and difficult to resolve.
