Influenza and the weather

By: Dr. Jeff Masters , 1:14 PM GMT on May 04, 2009

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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

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ATMOaggie--

That's awesome and good to know! Thanks!
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Quoting SomeRandomTexan:


WOW! Well my heart truely goes out to people like your in-laws who were so adversely affected from IKE. Luckily I didn't have any damage from neither IKE or RITA. We have a huge freshwater canal that is close to our house and acts as a levee to keep any on-comming water out. Though a lot of my friends from Bridge City were completely wiped out. I think 7 homes were all that didn't flood in Bridge City, a town of 10,000. So you studied at Lamar U? I am currently studying there as well.


Glad you didn't get flooded out.

Cool. I liked Lamar. Half the cost of A&M, no huge classes, profs with PhDs from Brown, Cornell, Yale, and the like, never walked more than 5 minutes to get to a class.
Had to transfer, as a junior, to A&M to finish a met degree, which I do not regret, and never saw where A&M teaches 600 students some required course in a room with stadium seating (and usually held by a grad student with a bad accent). And I almost never had to take the 20 minute bus ride to get to my next class, as the ones I had left were all in one corner of campus once I got there.

I would recommend getting a degree at the smaller schools to anyone (I have heard from refinery managers and the like that a Lamar engineering grad gets hired and paid the same as an LSU or A&M grad). And if your particular degree is only available at a larger school, transfer in after taking all of the first 2 year's worth of courses at a small school...the trick is to communicate with an advisor in the large school during every registration period or you could lose credits when you do transfer.

Back later.
Member Since: August 16, 2007 Posts: 6 Comments: 12461
At the moment, a non-tropical low to the south of the Azores may have the highest potential to become something in the Atlantic. Shear is low, between 5 and 20 knots surrounding and over the system; however, water temperatures are only around 70 degrees. While it is extremely unlikely, it is possible that this could slowly transition into a subtropical storm if it sticks around long enough and the shear remains reasonable. After looking at the quickscat, it appears that there are already some 25 knot winds with this system.
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Quoting atmoaggie:


I lived in Nerdland and went to Lamar U for a few years and my wife is from PA.

Did Ike flood your home...where you are describing is pretty low.

My in-laws, in Nerdland, got it bad with Ike. Got the roof peeled off, lots of water in the attic, collapsed ceilings, mold in walls, etc. They didn't flood, but the house needed to have everything inside stripped down to studs and slab and rebuilt...just like a flood.


WOW! Well my heart truely goes out to people like your in-laws who were so adversely affected from IKE. Luckily I didn't have any damage from neither IKE or RITA. We have a huge freshwater canal that is close to our house and acts as a levee to keep any on-comming water out. Though a lot of my friends from Bridge City were completely wiped out. I think 7 homes were all that didn't flood in Bridge City, a town of 10,000. So you studied at Lamar U? I am currently studying there as well.
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Quoting SomeRandomTexan:


between Orangefield and Bridge City

are you from the area?


I lived in Nerdland and went to Lamar U for a few years and my wife is from PA.

Did Ike flood your home...where you are describing is pretty low.

My in-laws, in Nerdland, got it bad with Ike. Got the roof peeled off, lots of water in the attic, collapsed ceilings, mold in walls, etc. They didn't flood, but the house needed to have everything inside stripped down to studs and slab and rebuilt...just like a flood.
Member Since: August 16, 2007 Posts: 6 Comments: 12461
Here's a link to an interactive map on the flu outbreak:

Global Incident Map

After you zoom in, you can click on an icon and get the latest news item for that.
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438. JRRP
Member Since: August 16, 2007 Posts: 0 Comments: 5337
437. Skyepony (Mod)
by far the most purple we've seen all year.
Member Since: August 10, 2005 Posts: 161 Comments: 37342
Nice update Weather456... could be the first official!
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Quoting TampaSpin:


IMO it has not been overplayed. CDC and WHO even today does not know what the outcome of this will be. Mutation of a Virus like this can occur overnight with a real Killer. Yes, the current Strain does not appear bad. But, the Mutated sister or brother could be a Psycho Killer!


When a virus mutates, it's a single copy that's different; even if the parent strain is world-wide, the deadly new strain would have to spread again. Furthermore, the only difference between this strain and the A(H1N1) strains in the usual seasonal flu is that this one is less like anything that people's immune systems currently respond to. If this strain spreads world-wide in a mild form or is included in seasonal vaccines, even that difference goes away.
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Quoting atmoaggie:


Orangefield? Vidor? Bridge City?


between Orangefield and Bridge City

are you from the area?
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Quoting CaneWarning:


I always enjoy your updates.


Thank you. Much appreciated.
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Unofficial African Easterly Wave Confirmed
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419: Interesting. I never realized Siberia was that low.
Member Since: August 16, 2007 Posts: 6 Comments: 12461
Quoting Weather456:
Good Afternoon - an interesting wave-like feature near the prime meridian, north of 0N.

Tropical Update


I always enjoy your updates.
Member Since: April 26, 2009 Posts: 3 Comments: 3667
Quoting SomeRandomTexan:
Stillwaiting--

Im in the very Southeastern corner of Texas right outside of a small town called Orange... right at the top of Lake Sabine... very wet, humid and hot here.


Orangefield? Vidor? Bridge City?
Member Since: August 16, 2007 Posts: 6 Comments: 12461
Quoting Patrap:
I read that this am as well..but I feel Like Van Heerden on the matter..



We showed the Atmocean Upwelling System to hurricane expert Dr. Ivor Van Heerden.

“It's an interesting idea,” Van Heerden said.

Interesting, yes, but Van Heerden said while there are some merits to the science, even 100,000 pumps is far too small – literally a drop in the ocean.

“They have the energy of a 100,000 atomic bombs as they cross, so to really have a significant impact, you would have to cool a huge portion of the ocean,” Van Heerden said.

Van Heerden also believes a hurricane's 40 foot waves and 100 mph winds would tear apart the tubes.


Member Since: August 16, 2007 Posts: 6 Comments: 12461
intresting feature forming North of the Col/Venz border:Link
Member Since: October 5, 2007 Posts: 20 Comments: 4970
Good Afternoon - an interesting wave-like feature near the prime meridian, north of 0N.

Tropical Update
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Stillwaiting--

Im in the very Southeastern corner of Texas right outside of a small town called Orange... right at the top of Lake Sabine... very wet, humid and hot here.
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422. Thanks!!!
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lunch is almost done 10 mins left back to work for me
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Quoting SpicyAngel1072:
411. KEEPER

Can I have the link to that map?

Sorry about the CAPS I work in them
here it is

Link
Member Since: July 15, 2006 Posts: 169 Comments: 53296
411. KEEPER

Can I have the link to that map?

Sorry about the CAPS I work in them
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neverending story
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Gads, the gub'ment must be covering up the Great SwineFlu DieOff. Mentioned GlobalWarming...
...and the expectable avalanche of "You're NUTS!!!" fails to appear.

Invest in future beachfront property by purchasing cheap land now.

from a nice hard scifi site on GreenhouseEarth...
...though I think he took the sea level up ~30metres too high.
But even at a 75metre rise, LittleRock and Memphis would be seaports...
...and LakeOntario would be a part of the sea joining the AtlanticOcean.

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its baby eagle feeding time...

Link
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ne s a gettin more flooding rains in coming days
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Quoting KEEPEROFTHEGATE:
ya just interesting watchin the action slowly set up for season ahead


Especially the storms over Africa this time of year.
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Quoting SomeRandomTexan:
good morning everyone! anything happen overnight that I need to know about?



..The sun was not out,lol....just joking,are you on the dry side of tx(west) or the tropical side (east),lol?????
Member Since: October 5, 2007 Posts: 20 Comments: 4970
ya just interesting watchin the action slowly set up for season ahead
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Member Since: July 15, 2006 Posts: 169 Comments: 53296
yep thats about it pat
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Global Disease ALERT Map

Member Since: July 3, 2005 Posts: 420 Comments: 127546
good morning everyone! anything happen overnight that I need to know about?
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this in


Seismic and rockfall activity increasing. Explosive eruption likely in coming days; could occur at any time with little or no warning.

The growing lava dome is becoming increasingly unstable and should a dome failure occur it likely would result in a significant explosion producing high altitude (>30,000 ft ASL) ash plumes, trace to minor ash fall in parts of south-central Alaska, lahars in the Drift River Valley, and pyroclastic flows in the immediate vicinity of the volcano.
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Posted by: JeffMasters "The results of this study imply that global warming may significantly reduce influenza world-wide, since a warmer climate will also be more humid."

Does a more humid world climate necessarily arise from the ClimateChange modeling?
While I can see the warmer air containing more water per given volume, humidity is usually thought of as relative to the maximum water-carrying capacity of air at a given temperature.
(eg relative humidity as used in the influenza study cited)

As I understand it
maximum water-carrying capacity = 100% humidity = dewpoint
And the dewpoint saturation fraction of water increases ever more quickly as the temperature increases.

ie It would take twice as much water (within a given volume) to produce the same relative humidity at 22degreesC than it does at 9degeesC. (Kinda hard to get accurate readings from that chart.)

My question arises from the fact that water is the main greenhouse gas. If warmer climate automaticly means higher relative humidity, then the GreenhouseEffect becomes rapidly runaway:
higher temperature -> higher humidity -> even higher temperature -> even higher humidity -> etc

It seems to me that the only way out, slow things down would be
warmer world climate -> drier world climate (ie wetter air but lower relative humidity)
And I have read that the Amazonian rainforests are projected to become grasslands and savannahs under the GlobalWarming scenario......at least until major portions join the seas of the GreenhouseEarth
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Quoting TampaSpin:


IMO it has not been overplayed. CDC and WHO even today does not know what the outcome of this will be. Mutation of a Virus like this can occur overnight with a real Killer. Yes, the current Strain does not appear bad. But, the Mutated sister or brother could be a Psycho Killer!


True it is always better to be prepared in these situations,then not.However I think the media has overhyped this,as they do with almost anything...does need to be watched,indeed...buuuuuut remember:West nile virus,SARS and the Bird flu????...I'm going to have to put the H1N1 in that group!!!!
Member Since: October 5, 2007 Posts: 20 Comments: 4970
nrtiwlnvragn, I saw that too.

I think the concept is there but this way of doing it isn't exactly what I would call sound.

The way I see it the bouy's would be pushed all over the place by the wind and water a good 8-12 hours before a storm.
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I read that this am as well..but I feel Like Van Heerden on the matter..



We showed the Atmocean Upwelling System to hurricane expert Dr. Ivor Van Heerden.

“It's an interesting idea,” Van Heerden said.

Interesting, yes, but Van Heerden said while there are some merits to the science, even 100,000 pumps is far too small – literally a drop in the ocean.

“They have the energy of a 100,000 atomic bombs as they cross, so to really have a significant impact, you would have to cool a huge portion of the ocean,” Van Heerden said.

Van Heerden also believes a hurricane's 40 foot waves and 100 mph winds would tear apart the tubes.
Member Since: July 3, 2005 Posts: 420 Comments: 127546
Quoting stillwaiting:


The southern hemiphere will soon be entering there flu season.....that will be the true test to see if h1n1 gets stronger!!!!,we should not have to wait till fall,as our friends to the south will have to deal with it there entire flu season first,this appeared at the end of our season,IMO,the whole situation is being blown waaaaay out of praportion,IMO.........


IMO it has not been overplayed. CDC and WHO even today does not know what the outcome of this will be. Mutation of a Virus like this can occur overnight with a real Killer. Yes, the current Strain does not appear bad. But, the Mutated sister or brother could be a Psycho Killer!
Member Since: September 2, 2007 Posts: 178 Comments: 20439
Gm,all,cool wet pattern for the northeast this week.Only 52 degrees today
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Better hurricane warning system touted
Published: May 2, 2009


MIAMI, May 2 (UPI) -- The hurricane warning delivery system in Florida is mired in last-century technology and needs to be updated, a U.S. congressman says.

U.S. Rep. Mario Diaz-Balart, R-Fla., said Friday that while the National Hurricane Center in Miami is using the latest in cutting-edge science to find and plot the paths of hurricanes, the way its warnings are delivered -- the Cold War-era "beep, beep, beep" broadcasts on television and radio -- is a relic, The Miami Herald reported.
Member Since: July 3, 2005 Posts: 420 Comments: 127546
Quoting TampaSpin:


The mutated Virsus for next fall will be the big problem. This will linger all Summer and then more than likely explode this coming fall and winter. Doubt a vaccine will be available yet either. Usually takes 6 months to develop.


The southern hemiphere will soon be entering there flu season.....that will be the true test to see if h1n1 gets stronger!!!!,we should not have to wait till fall,as our friends to the south will have to deal with it there entire flu season first,this appeared at the end of our season,IMO,the whole situation is being blown waaaaay out of praportion,IMO.........
Member Since: October 5, 2007 Posts: 20 Comments: 4970
Quoting Orcasystems:
Blog Refresh
Mirror Site

Daily Area of Interest
Click to enlarge


Please send rain to Florida.
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Tips To Prepare Your Boat For Hurricane Season

(NAPSI)-Preparing for emergencies is a part of everyday life. Schoolchildren practice tornado drills. Hotels post evacuation routes. So why is it that many boaters in coastal areas don't always take the time to plan for tropical storms or hurricanes?

For boaters who answer "it's too complicated" or "I don't know where to begin," there are no more excuses. Leading boat insurer Progressive offers these simple tips to prepare for those severe storms:
Member Since: July 3, 2005 Posts: 420 Comments: 127546
Quoting TampaSpin:
A major eruption is going to occur within the next 24hrs from Redoubt.

http://tampaspinsweather.webs.com/volcanoearthquakespace.htm
Harmonics and steam, growing lava dome? Seismically active day
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Quoting RTLSNK:


Will send you a WU-mail.


Thanks.......
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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