The Pathogens That Came In From The Cold

Yesterday, we asked you about your climate-themed policy for avoiding respiratory infections, and got the above-depicted, below-described, set of answers:

• About 46% of respondents said “Temperature has no bearing on infection risk”
• About 31% of respondents said “It’s important to get plenty of cold, fresh air, as this kills/inactivates pathogens”
• About 22% of respondents said “It’s important to stay warm to avoid getting colds, flu, etc”

Some gave rationales, including…

For “stay warm”:

❝Childhood lessons❞

For “get cold, fresh air”:

❝I just feel that it’s healthy to get fresh air daily. Whether it kills germs, I don’t know❞

For “temperature has no bearing”:

❝If climate issue affected respiratory infections, would people in the tropics suffer more than those in colder climates? Pollutants may affect respiratory infections, but I doubt just temperature would do so.❞

So, what does the science say?

It’s important to stay warm to avoid getting colds, flu, etc: True or False?

False, simply. Cold weather does increase the infection risk, but for reasons that a hat and scarf won’t protect you from. More on this later, but for now, let’s lay to rest the idea that bodily chilling will promote infection by cold, flu, etc.

In a small-ish but statistically significant study (n=180), it was found that…

❝There was no evidence that chilling caused any acute change in symptom scores❞

Read more: Acute cooling of the feet and the onset of common cold symptoms

Note: they do mention in their conclusion that chilling the feet “causes the onset of cold symptoms in about 10% of subjects who are chilled”, but the data does not support that conclusion, and the only clear indicator is that people who are more prone to colds generally, were more prone to getting a cold after a cold water footbath.

In other words, people who were more prone to colds remained more prone to colds, just the same.

It’s important to get plenty of cold, fresh air, as this kills/inactivates pathogens: True or False?

Broadly False, though most pathogens do have an optimal operating temperature that (for obvious reasons) is around normal human body temperature.

However, given that they don’t generally have to survive outside of a host body for long to get passed on, the fact that the pathogens may be a little sluggish in the great outdoors will not change the fact that they will be delighted by the climate in your respiratory tract as soon as you get back into the warm.

With regard to the cold air not being a reliable killer/inactivator of pathogens, we call to the witness stand…

Polar Bear Dies From Bird Flu As H5N1 Spreads Across Globe

(it was found near Utqiagvik, one of the northernmost communities in Alaska)

Because pathogens like human body temperature, raising the body temperature is a way to kill/inactivate them: True or False?

True! Unfortunately, it’s also a way to kill us. Because we, too, cannot survive for long above our normal body temperature.

So, for example, bundling up warmly and cranking up the heating won’t necessarily help, because:

• if the temperature is comfortable for you, it’s comfortable for the pathogen
• if the temperature is dangerous to the pathogen, it’s dangerous to you too

This is why the fever response evolved, and/but why many people with fevers die anyway. It’s the body’s way of playing chicken with the pathogen, challenging “guess which of us can survive this for longer!”

Temperature has no bearing on infection risk: True or False?

True and/or False, circumstantially. This one’s a little complex, but let’s break it down to the essentials.

• Temperature has no direct effect, for the reasons we outlined above
• Temperature is often related to humidity, which does have an effect
• Temperature does tend to influence human behavior (more time spent in open spaces with good ventilation vs more time spent in closed quarters with poor ventilation and/or recycled air), which has an obvious effect on transmission rates

The first one we covered, and the third one is self-evident, so let’s look at the second one:

Temperature is often related to humidity, which does have an effect

When the environmental temperature is warmer, water droplets in the air will tend to be bigger, and thus drop to the ground much more quickly.

When the environmental temperature is colder, water droplets in the air will tend to be smaller, and thus stay in the air for longer (along with any pathogens those water droplets may be carrying).

Some papers on the impact of this:

• Cold temperature and low humidity are associated with increased occurrence of respiratory tract infections
• A Decrease in Temperature and Humidity Precedes Human Rhinovirus Infections in a Cold Climate

So whatever temperature you like to keep your environment, humidity is a protective factor against respiratory infections, and dry air is a risk factor.

So, for example:

• If the weather doesn’t suit having good ventilation, a humidifier is a good option
• Being in an airplane is one of the worst places to be for this, outside of a hospital

Don’t have a humidifier? Here’s an example product on Amazon, but by all means shop around.

A crock pot with hot water in and the lid off is also a very workable workaround too 😉

Take care!