Why Is Flu Common in Winter? | Hacker News Reader

Why Is Flu Common in Winter?

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52 pointspwg27 comments

Some believe lower natural production of immune-system-important Vitamin D (through less sun exposure) is a factor, though studies have been mixed:

http://en.wikipedia.org/wiki/Vitamin_D_and_influenza

(I'd guess higher levels of sunlight might also help sterilize viruses on surfaces and suspended in the air, but have no handy references supporting that theory.)

There's also the unlikely-but-fun fringe theory that fresh flu viruses regularly fall to Earth from space:

http://www.panspermia.org/panfluenza.htm

Perhaps either a certain part of Earth's orbit, or colder hemispheric temperatures, mean more falling space flu? :)

"Consider wearing a good-fitting mask, with no gaps around the nose or mouth, in public."

This can probably be abstracted. Any activity that makes people not want to hang out with you or be near you will reduce your odds of getting the flu.

They should introduce the "I Genuinely Have Tuberculosis" t-shirt as an effective control in formal study

Worth noting that the porous, "paper", type masks that you sometimes see people wearing (being in Tokyo right now I'm understating their prevalence), are entirely worthless for defending against viruses. They're too small for those masks to be effective.

They're good for blocking particulate matter though, so if you're trying to prevent blood spatter to the mouth, thumbs up.

The irony is that they're excellent for preventing aerosol droplets filled with virus from the wearer. Wearing one when infected is therefore responsible.

no, staying home and not getting your co-workers sick by bringing your sick to the office is responsible. Coming to work sick, even with a mask, is irresponsible.

They are surgical masks worn as a courtesy by people who have a cold, so as not to infect others around them. In that sense they do work effectively...

One of the big advantages of wearing a mask (any mask) is that it stops you touching your mouth. Most people touch their mouths dozens of times a day without even thinking about it, and it's a fantastic infection vector. Person with a cold sneezes, gets rhinovirus all over their hands, touches a door handle, you touch the door handle, you bite your nails - hello cold!

Whilst the individual little virii can get through one, they're usually not found airbourne on their own; aren't they in big globs of snot and phlegm and the like? Surely that is stopped by the mask.

This isn't a question that already doesn't have an answer. Researchers showed at the Common Cold Centre in London that body temperature has an impact on the likelihood of catching flu. The reasoning is that during the cold, less blood flows to the extremities to maintain core body temperature. This includes less blood flow to the nose.

Flu lives in the nose, and white blood cells are what attacks flu, so having less blood in the nose means less white blood cells which means less chance of killing the virus off before it takes hold.

>This isn't a question that already doesn't have an answer. Researchers showed at the Common Cold Centre in London that body temperature has an impact on the likelihood of catching flu.

That research was far from conclusive or scientific.

I always thought it was a simple matter of contagion being partly a function of proximity between people. Since proximity is more common in bad weather, with people staying indoors, the flu spreads more easily in winter.

Isn't it just that viruses survive longer at lower temperatures? As per wikipedia:

"Flu viruses can remain infectious for about one week at human body temperature, over 30 days at 0 °C (32 °F), and indefinitely at very low temperatures (such as lakes in northeast Siberia)."

That has always been my hypothesis. When you cough in the winter, germs are cooled and conserved on the ground. Then when someone brings in water or snow from their shoes, they are basically bringing in refrigerated puddles of germs.

Someone must have tried to verify this?

So what I've never been able to understand is how it works in areas which don't have cold winters.

For example, when I lived in Brazil (Rio de Janeiro), where the temperature never really goes below 65 F, I was surprised that everyone would tell me that people get colds/the flu not in the winter, but in the summer -- supposedly because the constant shifts between hot summer air and cold A/C indoor air made you more susceptible.

But it seems to be common "scientific" knowledge that flu is a wintertime thing. Is that not always the case, though? Are there places where it actually is a summertime thing? Or in places without much change in the seasons, is there no yearly variation?

Interestingly, this would make sense in the fringe theory posted by another commenter on this thread. If flu viruses fall to Earth from space somewhere in Earth's orbit, then it would simply be at some point in the orbit where it is winter in the northern hemisphere and summer in the southern hemisphere, confirming your observation that the flu seems to be more prevalent in the summer months of Brazil.

From TFA: "It's also fine in humidities above 98%, which you find in the rainy season in the tropics," she says, where the conditions outside resemble the environment the virus finds in the body.

http://en.wikipedia.org/wiki/Vitamin_D_and_influenza

I wonder if the drought and dryness is causing the Flu Epidemic in the USA this year.

A lot of time and money is lost in dealing with the flu each year. So if the owners of big buildings, public spaces, & mass transit installed humidifiers to combat the flu, I wonder how much of a difference would it make...

Something that has never quite made sense to me is, the flu virus is apparently very delicate.. drying out very quickly. However, it seems to thrive more in cold, dry conditions. How can this be? And to your point, would humidifiers help or hurt?

> would humidifiers help or hurt?

I'd imagine in humid conditions the pathogens bind with the fine water droplets in the air to form an aerosol, which (I assume) sticks to surfaces more readily whereas in dry conditions the contaminants would remain airborne far longer and stick to the mucosa once inhaled.

I wonder if in the future, government regulation will require central heating systems to come with built-in humidifiers. Seems like a heater without a humidifier has serious negative externalities.

That's awesome! Now if I could find a humidifier that is silent and that I don't have to fill every day.

I have a whole house humidifier like this http://www.amazon.com/gp/product/B0002U3654/ref=wms_ohs_prod...

Took an hour or so to install myself and needs a new $10 pad every year, which takes all of 5 minutes to swap out, but is otherwise maintenance-free.

and that is not a breeding ground for germs...

or for mold.

Put salt in the water, it will inhibit many microorganisms, and if some salt gets in the air it won't hurt you - and may even help see: http://en.wikipedia.org/wiki/Salt_therapy

(But only once, since the salt will stay behind as the water evaporates. Unless you change the water, in which case add some more.)

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