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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I hope the day gets better for you Stillwaiting and I do mean that sincerely.
Member Since: June 12, 2005 Posts: 6 Comments: 8186
its all out now.....
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have you two thought about having a bird watching sleep over???,lol
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I see 'time out' coming for the cranky one soon!
Member Since: June 11, 2008 Posts: 24 Comments: 5910
Quoting NEwxguy:
elo is an old rock group


I knew that rang a bell somehow, you are right, the Electric Light Orchestra, great video on u-tube of them doing Roll Over Beethoven!! LOL
Member Since: September 3, 2008 Posts: 0 Comments: 20938
136. HadesGodWyvern (Mod)
CHAN-HOM(0902) 03113 11117 14234 230// 92904=

18:00 PM UTC 04MAY
TS CHAN-HOM
11.3N 111.7E
Dvorak Intensity: T3.0
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shep:what field do you work in and how many degrees do you have?????
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you shouldn't tip anyone without ambition,what's the sense????
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Quoting stillwaiting:



If you don't like living here or the way things are run,what do you do to change things other than complain about it?????


Vote early and often in 2010 :)

Did someone put something in your cornflakes this morning, you seem a bit cranky. .
Member Since: June 12, 2005 Posts: 6 Comments: 8186
ahhh,yea there is shep...did you have to wikipedia that????,lol
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Quoting stillwaiting:
I'll tell you one thing for sure..there's a big difference between northerners and southerners.....seems like most down here(FL) were raised w/a total lack of common sense,IMO....(hope I'm still allowed to have one!!)
Again, you speak volumes. There's no common sense in living within your means???
Member Since: September 11, 2008 Posts: 9 Comments: 10084
129. HadesGodWyvern (Mod)
531
TCNA21 RJTD 041800
CCAA 04180 47644 KUJIRA(0901) 01171 11310 11244 260// 90814=

18:00 PM 04MAY
TY Kujira
17.1N 131.0E
Dvorak Intensity: T6.0

---
T6.0 95 kt (JMA-10 min) 115 kt(1-min) CAT 4
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Quoting theshepherd:
113
NOAA has it...


A cut-and-paste decoder that gives mandatory levels, significant levels, and a nice plot in almost no time? Please share that link!

(maybe tropicalatlantic is just gone and the mirror soon to follow)
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127. HTV
Quoting stillwaiting:
I can ignore most of them(Flo-ridians),because so many of my northerners are taking this place over,I just enjoy the heck out of our weather though!!!and in 15-20yrs It'll be all but ours!!!!

This Southern Boy's common sense tells me I better just leave this one alone.
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Quoting theshepherd:
97. stillwaiting 12:55 PM EDT on May 04, 2009
Just curious shep,did you have health insurance when you were 31???...
**********************************************************************************************
Of course. And I made sure child was covered.

101 stillwaiting
question:If their was a deadly flu outbreak in the USA,would it be better if we had nationalized health care????or not??????
**********************************************************************************************
No, it would be better if most people had their own insurance. The County Health Clinics and County subsidized hospitals have always performed quite well.
Keep on though,your support is growing, those who rob Peter to pay Paul always have the loyal support of Paul.




If you don't like living here or the way things are run,what do you do to change things other than complain about it?????
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Atlantic anomalies are a mix bag as the Eastern Atlantic continues with cooler waters,the Western Caribbean is average while the Central Atlantic,Eastern Caribbean and Western Gulf are above average.

img
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Quoting Ossqss:


It is still registered with the search engines, just might be down or if located near SF CA affected by the fiber cut .


I think it is hosted in Tampa. Plus it would take a full day or more for it to disappear off of nameservers.
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113
NOAA has it...
Member Since: September 11, 2008 Posts: 9 Comments: 10084
I can ignore most of them(Flo-ridians),because so many of my northerners are taking this place over,I just enjoy the heck out of our weather though!!!and in 15-20yrs It'll be all but ours!!!!
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Quoting atmoaggie:
As a partial answer to my own question, see http://www.hhrecon.com/recon/.

Very similar to tropicalatlantic.com. OK, at the bottom, it says it is a mirror.


Cannot access it either.
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Quoting CaneAddict:


Have you tryed different URL extensions like .net .gov. .org?


It is still registered with the search engines, just might be down or if located near SF CA affected by the fiber cut .
Member Since: June 12, 2005 Posts: 6 Comments: 8186
Tropical Update
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I'll tell you one thing for sure..there's a big difference between northerners and southerners.....seems like most down here(FL) were raised w/a total lack of common sense,IMO....(hope I'm still allowed to have one!!)
Member Since: Posts: Comments:
Quoting atmoaggie:
Guys,

Did http://tropicalatlantic.com disappear? I cannot even find it on any nameservers.

If you can access it, please let me know and try to get the IP address. That would simply mean they have a nameserver issue, but we could still access it directly by IP.

Any other way of thoroughly decoding a dropsonde?


Have you tryed different URL extensions like .net .gov. .org?
Member Since: Posts: Comments:
As a partial answer to my own question, see http://www.hhrecon.com/recon/.

Very similar to tropicalatlantic.com. OK, at the bottom, it says it is a mirror.
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Quoting TampaSpin:
Stillwaiting so you work for a company that does not offer you Health Care?



I'm a waiter at a italian resturaunt,They don't offer me a thing!!!!
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111
That speaks volumes, Doc...
Member Since: September 11, 2008 Posts: 9 Comments: 10084
Guys,

Did http://tropicalatlantic.com disappear? I cannot even find it on any nameservers.

If you can access it, please let me know and try to get the IP address. That would simply mean they have a nameserver issue, but we could still access it directly by IP.

Any other way of thoroughly decoding a dropsonde?
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elo is an old rock group
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Quoting stillwaiting:



It seems like its been so long since we've had a president who can speak so eliquintly.....Obama reminds of JFK and Reagan more and more!!!!!,but only history will be the true judge of all of his actions.....


Please allow me to help you guys out this afternoon, I think the word you are looking for is not Eli quintly, but Elo quently. Eli was the guy that invented the cotton gin I think, but don't hold me to that. I'm not sure if Elo invented anything, but from what I remember, he was a very good speaker! LOL :)
Member Since: September 3, 2008 Posts: 0 Comments: 20938
LOL HTV---

the other day his teleprompter messed up and he introduced the same person twice....hahaha!
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109. HTV
Quoting stillwaiting:



It seems like its been so long since we've had a president who can speak so eliquintly.....Obama reminds of JFK and Reagan more and more!!!!!,but only history will be the true judge of all of his actions.....

His teleprompter, doesn't leave home without it.
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I have never been so grateful as I am today when the weather alarm went off for Severe t-storm watch. Need the rain BADLY.
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Quoting Patrap:

Vostok, Antarctica wu-page

-89 °F
Clear


Wow minus 89....no grass growing there....WOW! Well maybe some indoor type..LOL
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97. stillwaiting 12:55 PM EDT on May 04, 2009
Just curious shep,did you have health insurance when you were 31???...
**********************************************************************************************
Of course. And I made sure child was covered.

101 stillwaiting
question:If their was a deadly flu outbreak in the USA,would it be better if we had nationalized health care????or not??????
**********************************************************************************************
No, it would be better if most people had their own insurance. The County Health Clinics and County subsidized hospitals have always performed quite well.
Keep on though,your support is growing, those who rob Peter to pay Paul always have the loyal support of Paul.

Member Since: September 11, 2008 Posts: 9 Comments: 10084

Vostok, Antarctica wu-page

-89 °F
Clear
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Stillwaiting so you work for a company that does not offer you Health Care?
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Quoting stillwaiting:
GO RAYS!!!...NOT,last year was a fluke year for the rays and they got lucky,but as the WS proved they suck and now there right where they should be LAST PLACE,lol....GO YANKS!!!


You are one that waits for handouts and gifts from others.....LMAO..Yanks will end up 4th in the East at the end...trailing the RAYS, Sox, and Jays!
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Shep:that Ice shelf collapse is last weeks news..

question:If their was a deadly flu outbreak in the USA,would it be better if we had nationalized health care????or not??????
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GO RAYS!!!...NOT,last year was a fluke year for the rays and they got lucky,but as the WS proved they suck and now there right where they should be LAST PLACE,lol....GO YANKS!!!
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An area of an Antarctic ice shelf almost the size of New York City has broken into icebergs this month after the collapse of an ice bridge widely blamed on global warming, a scientist said Tuesday.

"The northern ice front of the Wilkins Ice Shelf has become unstable and the first icebergs have been released," Angelika Humbert, glaciologist at the University of Muenster in Germany, said of European Space Agency satellite images of the shelf.
**********************************************************************************************

Considering a very active seismic winter:
Would it not be nice if the geologists,who never look up and the climatologists(except it seems for temperature and currents) who never look down, could sit down at the same table and have a chat?


Member Since: September 11, 2008 Posts: 9 Comments: 10084
Just curious shep,did you have health insurance when you were 31???...tonights glenk beck should be great,I think I'm going to Tivo it so I can watch it until it brainwashes me,lol(just kidding,that guys reminds me of bill o'riely's step brother).....
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Atlantic Basin,GOES-12
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Quoting NEwxguy:


Hey,Tampa, I think Crawford is making a special trip to Yankee stadium so he can steal 5 more bases


Great and special gifted Athlete. Most at that level are gifted. Some just a little more.
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Quoting theshepherd:
People who live in glass houses....BTW, have you paid your Health Ins premium this month or are you "stillwaitng" for us to do it for you.



Ha,Ha....lol,nope "stillwaiting",lol....
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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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