Influenza and the weather
It is well known that influenza hits hardest in winter--November to March in the Northern Hemisphere, and May to September in the Southern Hemisphere. In fact, the name influenza comes from the Italian word influenza, meaning "influence"--referring to the "influence of the season" (winter) in causing the illness. In the tropics, where there is little change in seasons, influenza occurs year-round (though increased incidence has been noted in rainy seasons--Viboud et al., 2006). Do the cold temperatures and lower humidities of winter cause increased transmission of the flu virus? If so, why is the current H1N1 swine flu outbreak doing so well, now that it is May, traditionally the end of flu season in the Northern Hemisphere? Or could it be that indoor crowding, lack of sunlight lowering vitamin D levels, and a more depressed immune system in winter are largely responsible, as some researchers have suggested?
Flu infections increase under cold or dry conditions
To test these hypotheses, researchers at the Mount Sinai School of Medicine in New York did a study in 2007 that looked at flu transmission among guinea pigs, which are highly susceptible to human influenza and easily transmit the virus to other guinea pigs (Lowen et al., 2007). The animals were placed in adjacent cages, so that infections could occur by airborne transmission, but not by direct contact (guinea pig lovers will be happy to know that the influenza virus-infected guinea pigs did not display detectable symptoms of disease--weight loss, fever, sneezing, and coughing--during the experiments). By carefully controlling temperature and humidity, the scientists were able to study the effects of each. They found that the animals shed much more of the virus--and over a longer period of time--at cold temperatures, which led to increased infection rates. The animals' immune system showed no signs of stress from the cold weather, arguing against the idea that cold conditions lead to increased infections by lowering the immune system. Lower humidities were also found to increase flu transmission rate, though the variation of infection rate with humidity was more complicated. The scientists built a model (Figure 1) to fit the data, and proposed that lower humidity increased infection rates through two mechanisms:
1) The stability of influenza virons in the suspended aerosol particles infected creatures cough out is dependent upon the humidity. Viruses are most stable at low RH (20%-40%), least stable at intermediate RH (50%), and stable again at high RH (60%-80%) (Schaffer et al., 1976). Thus, the virus has better staying power at the low moisture levels typical of winter.
2) At high RH (80%), exhaled respiratory droplets grow quite large as water vapor condenses around them, and these drops quickly settle to the ground under the force of gravity. Thus, even though the virus is stable at high humidities, it settles out of the atmosphere quickly, and cannot contribute to influenza virus spread.
Figure 1. A model of influenza transmission rates at 68°F (20°C) (dashed line) and 41°F (5°C) (solid line), as a function of relative humidity. Transmission efficiency is highest at low relative humidity, when influenza virions in an aerosol are relatively stable, and exhaled respiratory droplets stay small and don't settle out under the force of gravity. Transmission is diminished at intermediate humidity when virus particles are relatively unstable, but improves in parallel with influenza virus stability at higher humidities. At high humidity, evaporation from exhaled particles is limited, respiratory droplets settle out of the air, and transmission is blocked. At cold temperatures (solid line), transmission is more efficient than at warm temperatures (dashed line), but is reduced to a rate of 50% at higher humidities. Image credit: Lowen, A.C., S. Mubareka, J. Steel, and P. Palese, 2007, "Influenza Virus Transmission Is Dependent on Relative Humidity and Temperature", PLos Pathogons, October 2007.
The researchers found no guinea pig infections at 86°F (30°C), which implies that in tropical climates, people may transmit the virus by direct contact rather than by coughing and sneezing. A second study Lowen et al., 2009) confirmed this idea--at least among guinea pigs. The authors concluded, "To our knowledge, we demonstrate for the first time that cold temperatures and low relative humidity are favorable to the spread of influenza virus. Although other factors likely contribute to the periodicity of influenza epidemics, it is clear that air temperature and RH could play an important role. Influenza virus transmission indoors could potentially be curtailed by simply maintaining room air at warm temperatures (>20 °C) and either intermediate (50%) or high (80%) RHs".
Climate change and influenza
The results of this study imply that global warming may significantly reduce influenza world-wide, since a warmer climate will also be more humid. Typically, there are between three and five million cases of severe flu and up to 500,000 deaths worldwide each year. In the United States alone, an average of 41,400 deaths and 1.68 million hospitalizations are attributed to influenza each year. A warmer world should reduce these numbers, if the current research is correct. However, these gains must be balanced against the possibility that malaria will become more widespread in a warmer world, since malaria kills about one million people per year.
Figure 2. Combined flu and pneumonia deaths in the United Kingdom during the great 1918 flu pandemic showed that the flu had three distinct peaks: one in June - July (a relatively mild form of the disease), followed by an extremely deadly outbreak in October, then another during the winter of 1918 - 1919. The 1918 flu pandemic infected 1/3 of the world's population, killing 50 - 100 million people. Strangely, the October peak occurred almost world-wide, with Bombay, India and Boston, Massachusetts peaking the same week. Image credit: Jordan, E., "Epidemic influenza: a survey", Chicago: American Medical Association, 1927.
Flu pandemics show little seasonality
The current Mexican H1N1 swine flu outbreak is seemingly unusual, since it is hitting at the end of the traditional flu season, in April - May. However, when a new flu strain develops that humans have no immunity to, the new strain is less constrained by seasonality. According to Dr. Jeffery Taubenberger, the virologist who helped isolate the genetic code of the virus responsible for the great 1918 flu pandemic, "Historical records since the 16th century suggest that new influenza pandemics may appear at any time of year, not necessarily in the familiar annual winter patterns of inter-pandemic years, presumably because newly shifted influenza viruses behave differently when they find a universal or highly susceptible human population." Indeed, the 1918 flu pandemic reached its peak in September - October (Figure 2), and the most recent flu pandemic, the 1968 Hong Kong flu, began in July. It wouldn't surprise me if the current flu outbreak dies down in the Northern Hemisphere over the summer months, as the combined effects of high temperatures, higher humidities, less indoor crowding, and increased sunlight interfere with its spread. However, we need to be ready for the virus to reappear in the Fall--potentially in a mutated, more virulent form--such as occurred during the 1918 flu pandemic.
References
Lowen, A.C., S. Mubareka, J. Steel, and P. Palese, 2007, "Influenza Virus Transmission Is Dependent on Relative Humidity and Temperature", PLos Pathogons, October 2007.
Lowen, A.C., S. Mubareka, J. Steel, and P. Palese, 2009, "High Temperature (30°C) Blocks Aerosol but Not Contact Transmission of Influenza Virus", Journal of Virology, June 2008, p. 5650-5652, Vol. 82, No. 11 0022-538X/08/$08.00+0 doi:10.1128/JVI.00325-08
Schaffer, F.L., M.E. Soergel, and D.C. Straube, 1976, "Survival of airborne influenza virus: effects of propagating host, relative humidity, and composition of spray fluids", Arch Virol 51: 263-273.
Viboud, C, W.J. Alonso, and L. Simonsen, 2006, "Influenza in tropical regions", PLoS Med 3: e89 doi:10.1371/journal.pmed.0030089.
Vitamin D and influenza links:
http://www.medicalnewstoday.com/articles/51913.ph p
http://www.sciencedaily.com/releases/2008/08/0808 11195629.htm
http://www.vitamindcouncil.org/science/research/v itamin-d-and-influenza.shtml
Jeff Masters
Reader Comments
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"There are those of us, though...that go to the storm to bring to others information about these damn things."
News Flash:
IT"S A HURRICANE. STUFF BREAKS LOOSE, BLOWS AROUND AND GETS WET. PEOPLE DIE. LIVES ARE DESTROYED. HEROES APPEAR ON CAMERA.
You've told Jim Cantore this, have you?
I guess he should stay home, too huh?
Get real. It's an event that goes right to the top of national news. Do you honestly expect that men and women will not travel into these areas to deliver to you information about them?
Really? Wow...wake up and turn on the news.
Nice comeback.
Be more specific, please.
Both of us? [me and my baby girl] or just me?
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Finally.... a DAI with no RTLSNK in it.
You're talking to the wrong person, pal.
So...as a service to you, here's the entire policy on pictures here at Wunderground.com:
Approvals
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Rejected Submissions
If your photo does not comply with our guidelines, it is subject to rejection. Any of the following reasons may be given for an image that is rejected:
Subject Not Outdoors - All Wunder Photos must be either taken outdoors or depict a subject that is outdoors. Photos in which the subject is indoors and not weather-related are NOT accepted. Weather-related exceptions include storm damage and indoor photos depicting the size of hail.
Broken or missing image - The full-size image does not display correctly or was corrupted during upload.
Plagiarized Image or Copyright Violation - The image copyright belongs to someone other than the uploader. Please do NOT upload images that you did not take, or that contains copyrighted material.
Not site appropriate - The image is obcene or not appropriate for a weather & outdoor photography site.
Wrong date - The image was not taken on the date specified when you upload it.
Digital art - When the image has been altered so that it no longer looks like the original subject matter or incorporates artistic elements, it is considered digital art, which we do not accept. See our Manipulated Images FAQ for examples of what we mean.
If a photo you uploaded is rejected, it will show only in your "My Photos" page and the reason for the rejection will appear below the image. If you feel that it has been unjustly or mistakenly rejected, please send a message to WunderPhotoAdmin.
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Finally.... a DAI with no RTLSNK in it.
Action: Quote | Ignore User
i see ya nicely chopped out pretty well all of southern ontario
kinda useless crap if ya dont include entire area
Your daughter is beautiful and is going to need her Father dearly in years to come. First day at school, first busted knee on her bike, learning to drive, graduating high school, walking down the isle, etc. I pray you'll not do anything unthinking that would deprive her of that.
And no, infants don't need shirts.
Grown men on the other hand in the presence of strangers....
You talking to me??
I can add Southern Ont..
April 20-23 TS Ana 2003 formed west of Bermuda
May 6-9 TS Arlene 1981 formed from disturbance that moved from Pacific across Central America to Caribbean
May 9-11 TS Andrea 2007 formed 150 mi north east of Daytona Beach, Fl
May 15-23 Hurricane Able 1951 formed 300 miles so of Bermuda
May 17-26 Hurricane Alma 1970 formed in Southern Caribbean
May 23-29 TS Alpha 1972 formed off east coast
May 25-June 6 TS Alice 1953 formed in the Caribbean
May 28-31TS Arlene 1959 was first noted near Dominican Republic on May 23
May 30-June 2 TS Arthur 2008 formed near Belize.
1908 was interesting:
Unnamed Hurricane One 1908 March 6-9 noted at St.Kitts and Nevis recorded 991mb
Unnamed Hurricane Two 1908 May 24-31 formed north of Hispanola
And I agree with you, Orca!
What a nice thing to say to me in public! U Da Man!
See to you??
I'll go ahead and say it - you are cocky for no apparent reason.
and i hope yer flush model works better this year
g'night
You know what, Shep. You're right. I'm wrong.
FIRE SALE - HURRICANE SUIT FOR SALE; Never used! HURRICANE REMOTE WEATHER STATION FOR SALE - Never used! HURRICANE HUNT VEHICLE FOR SALE! 105,000, but in great shape. Only been to four hurricanes...so buy now!
All offers accepted!
Oh man... I am going to get you for that.
Mind you.. Southern ont... Quebec... same same.
Mr. Oz, all the best in your adventure. You have a game plan and I respect that for sure. Along with your ability to alter a blog.
I would not compare you with the weatherchannel's budget and preparation, but be safe and have fun, is all I can say :)
The personal attacks [that I never start, btw], ...well they both offend and annoy not only myself, but others.
If you do not find my comments to your liking, simply press the ignore button. Simple.
Personal Attacks - bad.
Ignore Button - good.
Concerning the whole covering hurricanes up close and personal thing, I'm with CycloneOz on this one. As long as one knows what he/she is doing, wears the proper prospective equipment, and has an exit plan if things go bad, let that person cover the storm in the matter that he/she sees fit.
Good trade.
Buy a webcam. Strap it to that parking deck you mentioned and stay home and hold that child tight. Because that storm is gonna scare hell out of her.
Your aware its included with GE?
Orca - I'd never call you cocky. I was referring to the other one with the attitude.
What he really means here is psycho Oz.
Okay...let's do this one more time then for those not paying attention.
Personal attacks - bad.
Ignore button - good.
[I'm pressing the ignore button next!]
Please do.
Thought that might have been it... hehe normally I am called far worse :) Thought I might be slipping.
is it me or is everone going nuts
What do you mean nuts :)
Oz, I like the new name :)
You're so cute when your dorsal fin gets all in a wad....ducking under desk lmao
No...he was talking about me, Ovumsystems.
a killer whale is not meant to be cute don't be fooled its a ferious mammal that will trash and bash you to a lifeless bloody pulp
Hey now.. we all know I am sweet and innocent.. note the Halo on my head :)
It looks just a little crooked...
Crooked, heck that is dyslexically viscous photoshopping. Yep, kinda real word.
I spelled it right :) Orca nothin personal
Link
I very much appreciate that. I don't do anything without a plan, especially this particular thing.
Good thing, too...because they wouldn't rate against what I do. Here's some real facts for comparison.
TWC - The WeatherChannel can't do HD in a hurricane. Nope. It's their uplink. It can't handle the bandwidth, so they shoot and upload SD.
Me - I shoot HD. Period.
------------------------
TWC - Their on-camera, hurricane weather gear is simply the clothes on their back, a flimsy, shiny plastic jacket and swimmers goggles.
Me - My hurricane weather gear is extensive and expensive.
-----------------------
TWC - You think those news guys have alot of money...but no. They're flat broke. When I showed them my footage from Dolly in the lobby of the hotel [i.e. transformer / patio deck explosion], they offered me $100 bucks for the footage.
ME - What services I perform may entertain at times, may make some laugh...but eventually I'm gonna get the terrifying stuff and that, hopefully, will get some people to evacuate who ordinarily would not consider it. And I do it for free on my own dime.
BF gave it to me.. its almost brand new.. came with a 45 gallon barrel of Halo polish to boot :)
You just jealous because your Staff has a crook in it.
ROFLMAO :)
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