It’s the week between Christmas and New Years. A mind-numbing, limb-aching cold has settled in and houses are packed with food, drink, warm bodies, merry microbes and humble viruses. If your family is anything like mine, then the holiday season is usually a time when sickness runs rampant. It arrives as a variety of visitors, but it almost always comes knocking at the door.
Seven years ago, it was the foodborne illness from hell that came in the shape of a New Year’s Eve pad thai thrown together by a violently ill family member. This year, sickness came in a visitation from a respiratory virus for some of the adults and a gastrointestinal horror show for the kids. I have managed to escape this year’s plague and am hoping my B-cells keep putting in the holiday overtime; however, I am cautiously optimistic as the threat is alive and it is everywhere.
Oh The Weather Outside is Frightful
So, is there any evidence behind this apparent influx in communicable illness over the Christmas season?
Is there an increase in unwanted hitchhikers when the snow and ice arrive or does our immune system take a vulnerable hit from all the holiday spirit?
Or is it just the fact that we are likely to spend time with usually absent relatives who often forget to wash their hands and double dip on the holiday appetizers?
It’s a little bit of a mix bag, unfortunately.
The seasonal cycle of disease and infection has been a long-observed phenomenon starting all the way back in the 18th century when physician William Hillary wrote on the variations of weather and disease, focusing on tropical climates and the diseases found rampant within. Despite the ongoing interest in the pattern of weather and illness, it remains very difficult to understand it, quantify it and explain it’s apparent existence. This seems to be due in part to the many factors that cumulate to create the phenomenon.
So, lets take a closer look. What are the big things that make us sick and why does it seem to occur at the same time every year?
If you take a dive into the data and swim around the various studies on the matter, you find some common considerations:
- The ability of the pathogen to survive (this is the nasty thing that makes your nose leak and your stomach churn)
- How the host behaves (this is you)
- How does the host’s defensives hold up (this is your immune system)
These main considerations intertwine in a convoluted web of dizzying interactions with each other, environmental conditions, vitamin D metabolism, and even territorial fights with other pathogens. It is a messy, complex relationship and illustrates why there is no clear-cut answer to the question – Are the cold, snowy winter holidays with Aunt Norma making me sick?
Bacteria and viruses are two very different and very complex classes of pathogens.
Bacteria are unicellular organisms that are mostly harmless. They are hitchhikers that live on our skin and in our guts (our normal flora) and have, at some point, been absorbed into our very cells (mitochondria’s hypothesised origin).
Although, most bacteria are harmless, if they end up in the wrong places – E. Coli outside of the cozy intestinal tract or Staphylococcus Aureus deep into tissues through open wounds– our bacteria friends become our worst enemies.
Still, there are certain kind of bacteria we need to be weary of. Pathogenic (disease causing) bacteria are the kinds that usually cause us the most trouble, including species that cause nasty illnesses like: pneumonia, tuberculosis, and meningitis.
Viruses (like influenza, rhinovirus, and the lovely bouquet of gastrointestinal viruses) are often the holiday visitors that drop in unexpectedly, start fights and drink all your good wine before passing out on your living room floor.
Whether, your holiday visitors are bacteria or viruses, it appears that weather and seasonal changes can influence the ability for these bugs to survive and even thrive. Temperature, humidity, pH and salinity (fancy word for salt) are all environmental factors that affect pathogens.
Low temperatures seem to enhance the survival of the lovely gastrointestinal viruses and there appears to be a noticeable increase of illness when the cold weather hits. For the viruses that like to hang out in the air, they are likely to survive floating around our homes when the humidity is low. Your furnace blowing hot air into the room or your fire place crackling away sets up the best environment for optimal transmission of these guys.
When microbes and viruses are in peak form, they are more infectious, more virulent and plentiful. In short, it makes it harder for us to get them to leave.
This is only one part of a very complex picture. It gets increasingly complicated when we add us into the equation
Hey, that’s you. The things that make you sick, can only last so long outside of the comfy, cozy corners of your body. They are going to find a way to make it inside or die trying. In this scenario, how the host behaves when the colder weather settles in is important. Especially regarding the increase of opportunities for a visitor to sneak in to your holiday party.
Human behavior in the dead of winter is pretty universal. We tend to spend too much time indoors and congregate closely with other people, especially around Christmas and New Years. Lots of bodies, lots of food and lots of opportunity for the transmission of infectious pathogens.
The data is pretty fuzzy on this one and mostly subjective. It’s hard to quantify, or calculate, the importance of host behaviour in this seasonal infection equation, but it continues to pop up in study after study. It’s not so insignificant as to be written off entirely but it’s hard to explain exactly how it affects the other variables.
There is one thing that is very important about you, the host, and that is how you defend yourself from the unrelenting onslaught of things that will make you sick.
The Immune System
In the same way changes in the environment affect the pathogens themselves, they also affect our defensives. And, unfortunately for us, it has the opposite effect. Our immune responses generally take a hit around the holidays.
Our humoral immunity involves cells called B-Cells that create little Y shaped antibodies. These antibodies are able to bind to pathogens impeding their progress inside our bodies. Our cell mediated immunity involves cells that phagocytose, or eat, these pathogens — effectively kicking them out of the party. Both of these immune responses change with seasonal variations.
There are a few hypotheses why but one involves the decrease in Vitamin D metabolism. The “sunshine vitamin,” so adorably named because sunlight is needed in its synthesis, declines in winter. There is evidence that Vitamin D plays a role in the function and regulation of our little phagocytes (the cells that devour others). A deficiency may cause impaired immune function, opening up our doors to unchecked guests.
The internal line of defense isn’t the only part of our immune system that may be affected. Remember how the viruses love to hang around in warm, dry air? Well, that warm dry air does not do us any favours.
Our first line of defense, our innate defense, involves our skin and mucous membranes — both tend to crumble in hot and dry conditions. Our nasal passages in particular take a pretty heavy defensive hit. There appears to be both a change in mucus production and cilia (little cells that beat back and forth to clean out unwanted particles) action.
Your mucus contains something called lysozyme, an enzyme that can break down bacterial cell walls, while your cilia beat away most unwanted visitors. Dry air is not favourable for optimal function of either of these mechanisms and a decline in their activity leave us feeling vulnerable, much like your third glass of wine while looking at photos of your unrequited love.
So, if you find that you have an uninvited guest overstaying their welcome this holiday season, rest assured you are not suffering alone. Whether said guest is your uncle that refuses to wear pants or a happy little virus setting up shop replicating its DNA inside of your cells until they burst open like piñatas, know that the holidays bring out the best and worst in all of us.
Images: Erin Matthews
Seasonality of Infectious Diseases. David N Fisman. January 2006.
Seasonal infections disease epidemiology. Nicholas C. Grassy and Christophe Fraser. July 2006.