Can someone explain to me the geography of seasonal flu? Is it the northern countries that experiences flu season from October to January? Does that mean that southern countries experience flu season in the Summer? Or do I have this completely confused?
Also, why is this? I would’ve thought that in this era of modern travel there wouldn’t be such a thing as seasonal flu — that it would always spread year-round…if you follow my reasoning…
I’ve asked this question as well and don’t knopw if I’ve gotten it all answered. I do know that one factor in the Northern hemishpere is that it tends to get worse as we spend more time crammed together indoors during the colder months. Here in the US it really starts to take off in December/January (holiday travel season) through March, although there are outbreaks earlier in some areas. There’s some impact that humidty plays as well, although I forget if it’s low humidity makes it worse or the other way around (anyone out there know?)
Problem with H5N1 right now is that the highest number of human cases are in semi-tropical/warm climates and the more recent outbreaks have been March-now (although techinically they are north of the equator). Throws that seasonlity theory right out the window doesn’t it? In 1918 the main thrust of the epidemic started in September - December, with lesser waves in the following year.
One theory out there is that in the winter, levels of vitamin D drop due to decreased sun exposure and that raises suseptability to flu. This was discussed not too long ago here, I don’t have a link, but I think you could do a search for vitamin D.
My understanding is that low humidity (brought on by central forced air heating) dries and irritates your nasal membranes, making them more accessible and fertile ground for microbes.
A good thing to do if you have forced air heat is to turn down the “high temp” setting for when the fan starts after the burner has been on. This temperature is often set very high, because people like the feel of that first burst of HOT air, and don’t want to feel any twinges of what may be a cool draft of cold air pushed around by the new hot air. The higher air temp (often 151°F) partially combusts the dust, pollen in the air, and makes it much more irritating and drying. Made a real difference in wintertime infections when I lived in Denver. Turn it down so the air feels warm but not HOT, no more than 120°F (I do 100), that’s plenty. See http://tinyurl.com/e5dla for details, about halfway down the page.
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