Respiratory Infections: Why Do They Happen More Often in Winter?
The influence of cold weather on the likelihood of contracting respiratory infections has been noted over hundreds of years. Influenza is derived from the Italian terminfluenza di freddo, which means "influence of the cold," and was used in Italy during the 1300s to describe the illness. While most have probably heard at least once in their lives that it's dangerous to go outside with wet hair because one will catch a cold, that is, in fact, a myth. As it turns out, lack of humidity is a significant driver of influenza infections in the winter. Influenza is spread by respiratory droplets in the air, which in warmer, humid weather take on more moisture and fall to the ground faster. In cold, dry climates, the respiratory droplets can stay in the air for longer, thereby infecting people more often. Combine this with indoor crowding and the closeness that comes with moving indoors and trying to stay warm, and it is a recipe for respiratory ruination.
Differing fates of large and small resipratory droplets.
One of the most significant challenges associated with cold winter months is a lack of fresh food, and human survival has long depended on storing enough summer and autumn food to last until spring. Research demonstrates that ancient hunter-gatherers used the help of bacteria living in lakes to preserve meat during the winter months. It is believed that after successfully hunting a mammoth, indigenous people placed the meat in small, cold lakes where lactobacillus bacteria produced lactic acid and preserved muscle mass. Lactic acid-producing bacteria have long been used in the food industry to prevent food spoilage, since lactic acid prevents bacterial growth and the production of biologic amines, which ultimately contribute to the breakdown and rotting of food. Simply stated, ancient hunter-gatherers figured out how to extend the “shelf-life” of the food they hunted.
Newspaper clipping following botulism outbreak in 1931.
In Canada, botulism outbreaks have been centered around the country’s native population since 1985. Most of the reported cases since 1985 have been due to the contamination of traditionally prepared marine mammal meat, particularly from seals and Beluga whales.
Clostridium botulinum is an anaerobic Gram-positive bacillus that produces one of the most potent known neurotoxins, which can cause muscle paralysis and death if ingested. Therefore, proper canning precautions must be taken to prevent contamination and subsequent illness when prepping food for a long winter (or quarantine).
The cause of such destruction onboard the trade ship was an infestation of rats, which carried fleas harboring the Yersinia pestis bacteria. These fleas found new hosts in their European and American destinations, ultimately infecting new rats. The rat population may have exploded, in part, due to increased biomass resulting from increased precipitation during the Little Ice Age. At the same time, the cool and humid conditions created by the Little Ice Ace may have supported flea survival and breeding. Combined with poor sanitary conditions and crowding, the plague killed over 20 million people in Europe by the end of the epidemic.
While the incidence of plague did not seem to increase during the winter months, the Little Ice Age serves as a great example of how cooler temperatures and climate change can significantly impact agriculture and cultural practices, which in turn may introduce pathogens into populations that have not previously experienced their wrath.
Make Winter Safer
The chill of the winter season encourages people to slow down, retreat and reflect. The increased hours of darkness and quiet allow one to think a little harder about staying healthy and protecting others during the winter season. To prevent the spread of respiratory viruses, cover your cough or wear a mask. Maintain distance from others if you are sick, and avoid attending or hosting crowded events. Ensure that all food is cooked and prepared correctly to prevent foodborne illnesses. Finally, consider steps that can be taken to help protect the planet and reduce the impact of climate change; we never know which pathogen is around the corner waiting for the opportunity (and ideal conditions) to strike.
Andrea Prinzi, Ph.D., MPH, SM(ASCP) is an infectious disease medical science liaison and works to bridge the gap between clinical diagnostics and clinical practice.