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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694. Skyepony (Mod)
Morning ya'll. Nasty in the SE. Looks like possible tornado fixin to go N of Birmingham, AL.
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You guys are making me think about this season's storms. I guess I'd better get ready. My hurricane prep list includes the following:

1. Get a list of hotels out of the area that will let me have 3 dogs

2. Get sedatives for dogs

3. Get bordatella shots for dogs (required for kenneling, in case I can't find anything for #1 or in case #2 doesn't work and they go nuts)

4. Get dog's teeth cleaned (b/c there is nothing worse than driving three hours with 3 dogs with stinky dog breath).

5. Figure out what few things I should take since after I pack all the dog stuff there is very little room left for our stuff. Oh, and bring a cooler in case I have to buy groceries out of town to bring back in town.

Once an evacuation is planned, I put up the plywood, pack the dogs and kid, throw my meager belongings in the glove box (it's the only empty space left) and hit the road!

With both Rita and Ike evacuations under my belt, I'm getting pretty good at this.
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Good morning everyone.
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Morning!
Member Since: August 30, 2007 Posts: 0 Comments: 1857
Sorry good morning everyone!
Member Since: September 2, 2007 Posts: 178 Comments: 20443
Quoting Orcasystems:


They do look impressive though

Link


You are correct. If conditions would be favorable models would be exploding with the wave coming off Africa. Just not much of a chance now for anything to develop into a named storm. It could become an Invest tho!
Member Since: September 2, 2007 Posts: 178 Comments: 20443
The Africa Blob looks really impressive... Even though there is little chance for it to mature into something more, it still brings back memories of last year of some of the mammoth blobs that moved off Africa. The least it will do is give us something to watch for a day or so...
Member Since: August 30, 2007 Posts: 0 Comments: 1857
Quoting Orcasystems:


Not to bad up here.. I hear thats the excuse the penns are using.


Ouch !
Member Since: June 12, 2005 Posts: 6 Comments: 8186

Animated National Radar View
Member Since: July 3, 2005 Posts: 426 Comments: 128639
impressive line of storms moving down... hope whoever needs the rain gets it!
Member Since: August 30, 2007 Posts: 0 Comments: 1857
Quoting Ossqss:
How is that SLIME flu doin Orca ?


Not to bad up here.. I hear thats the excuse the penns are using.
Member Since: October 1, 2007 Posts: 81 Comments: 26511
NOAA event teaches students hurricane preparedness

BY JONATHAN STARKEY | Special to Newsday
9:28 PM EDT, May 5, 2009

Lt. Cmdr. Al Girimonte, a 1991 graduate of West Babylon High School, returned to Long Island Tuesday at the controls of a Hurricane Hunter plane to stress storm preparedness as the hurricane season approaches.

Girimonte and his crew landed at Republic Airport about 9:15 a.m., piloting a WP-3D Orion, which Girimonte often flies into hurricanes to measure their strength and direction.

The event was part of a National Oceanic and Atmospheric Administration Hurricane Awareness tour that began Monday in New Hampshire and will end in South Florida later this week. About 400 students from seven local schools learned how to prepare for a storm and toured the aircraft.
Member Since: July 3, 2005 Posts: 426 Comments: 128639
How is that SLIME flu doin Orca ?
Member Since: June 12, 2005 Posts: 6 Comments: 8186
Quoting stillwaiting:
orca:whats up with your DAI map???,I think its old......there's a line of storms across the south!!!!( a looooong one)...


Hit refresh :)
Server seems to have a minute or two delay in it for some stupid reason.
Member Since: October 1, 2007 Posts: 81 Comments: 26511
orca:whats up with your DAI map???,I think its old......there's a line of storms across the south!!!!( a looooong one)...
Member Since: October 5, 2007 Posts: 20 Comments: 4970
Quoting WarEagle8:
Thank you all for the tropical updates. It is starting to look more like summer on the satellite images. I know the African blobs are very unlikely to develop this early in the season; however, they sure look like teasers.


They do look impressive though

Link
Member Since: October 1, 2007 Posts: 81 Comments: 26511
Blog Refresh
Mirror Site

Daily Area of Interest
Click to enlarge

I have learnt one thing from these DAI, don't live anywhere near RTLSNK, he is in all of them.
Member Since: October 1, 2007 Posts: 81 Comments: 26511
Thank you all for the tropical updates. It is starting to look more like summer on the satellite images. I know the African blobs are very unlikely to develop this early in the season; however, they sure look like teasers.
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What error have you gotten? I have not experienced any to date.
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674
Try a MAC... they can handle the new RADARs
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672. I've been getting that for a couple of days now. Thought it was just me.
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Whats going on with Nexrad radars, getting error messages everytime I click on any of them....
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Quoting melwerle:
Thanks Oss...was kind of hoping we'd see some of it...gives me an excuse to bail.

Have a great day!
Do really want to 'bail' while boating? LOL
Member Since: August 19, 2008 Posts: 6 Comments: 2490
Thanks Oss...was kind of hoping we'd see some of it...gives me an excuse to bail.

Have a great day!
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Quoting melwerle:
Hey RT and Oss - can't tell by looking at the map but do you think we'll get some of that by this afternoon here in Savannah? Supposed to sail this afternoon...


Just a guess, but it does not appear to be moving fast enough or South enough to impact you by then. Good luck and check locally for details to be safe.
Member Since: June 12, 2005 Posts: 6 Comments: 8186
Hey RT and Oss - can't tell by looking at the map but do you think we'll get some of that by this afternoon here in Savannah? Supposed to sail this afternoon...
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You got that right 659
Member Since: June 12, 2005 Posts: 6 Comments: 8186
Swine Flu Kills U.S. Resident as Pandemic Nears

Hope we don't have any trends.
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G'morning folks

70.6F - dew point 69F - another muggy day.
Missed most of the rain, but did get some drizzle. Is that rain I see on my horizon?
Should I break down and wash my car? Perhaps Snake will share?



Member Since: August 19, 2008 Posts: 6 Comments: 2490
Quoting Weather456:
Morning,

Tropical Update


Good morning Weather456.Nothing yet from TPC about introducing the first tropical wave.
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I know Vortex - it was raining nonstop for a week a month ago and I was starting to get a bit crazy but everything is dead around here right now - the sprinklers aren't even touching it.
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I'm the one who did the rain dance yesterday, RT...we got rain but really needed it!
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Morning,

Tropical Update
Member Since: July 24, 2005 Posts: 407 Comments: 19076
70*F, 94% humidity in Macon, Ga this morning.
Who was it that was doing that rain dance yesterday?
Remember that old saying "be careful what you wish for"?
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nevermind...found it
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653. Pat

Great image
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655. Patrap 12:41 AM EDT on May 06, 2009

Yep your correct Pat. Nearly no chance for anything to develop this early in that location.
Member Since: September 2, 2007 Posts: 178 Comments: 20443
The Far Atlantic isnt the area to even consider for development.
Its way to early for African,disturbed areas,AKA ,early waves to develop and Trek across the Basin.
Look to the Western Carribean,the BOC and GOM proper.

The Westerlies are still in control for now. But the change and easterly Flow will establish soon nuff.



Member Since: July 3, 2005 Posts: 426 Comments: 128639
Keep in mind i'm not saying an invest could not be claimed but, i'm saying a Tropical Storm will not develop in that location in the present conditions. As conditions are only 5 percent favorable for development in my Anyalsis and spreadsheet.
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Atlantic Ocean View (Updated ~3 hours) GOES-12 Channel 3 (WV)
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The interest at 5N 25W has a 5% chance in average conditions for Tropical Development to Develop.

(Average conditions are defined as the absolute needed for something to develop...ie. SST's of at least 26.5C is defined as average anything above is above average, anything below 26.5C is below average.)

Simply put i doubt anything will develop at that location.
Member Since: September 2, 2007 Posts: 178 Comments: 20443
Member Since: July 3, 2005 Posts: 426 Comments: 128639
Ok Tampaspin, could you tell me in a summarized analysis, what someone should take away reading your spreadsheet?(The overall thesis of the project). Want to make sure I understand you correctly...
Member Since: November 20, 2007 Posts: 21 Comments: 192
200mb-850mb/200mb Streamline,VALID
Member Since: July 3, 2005 Posts: 426 Comments: 128639
Quoting quasigeostropic:
TampaSpin, could you tell me where you got those numbers from on your spreadsheet? Did you think this up yourself? Or is this an actual publication somewhere? Curious.....


I did this myself....A project at home one day i was playing around with. If you scroll down the spreadsheet you can see the non-subjective entries as they are what they are.
Member Since: September 2, 2007 Posts: 178 Comments: 20443
MODEL GRAPHICS

Model Output Available Approximately 1100 & 2300 EST


Tropical Wind Shear & Streamlines : NGP Current Model Run
High Color Tropical Wind Shear & Streamlines : Current Model Run
Tropical Wind Shear Anal and Forecast : Current Model Ru
Member Since: July 3, 2005 Posts: 426 Comments: 128639
TampaSpin, could you tell me where you got those numbers from on your spreadsheet? Did you think this up yourself? Or is this an actual publication somewhere? Curious.....
Member Since: November 20, 2007 Posts: 21 Comments: 192
I concur with quasigeostropic on shear being more difficult to accurately pinpoint when it comes to a localized area. For example, when I was issuing forecasts for Hurricane Gustav last year on another forum website that I go to, each time I looked at the computer model forecasts of upper level vertical wind shear, I found that the wider areas of predicted shear (or lack thereof) could be predicted with a reasonable degree of accuracy -- it was the localized shear that posed the most problems.
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Here is my Analysis and Percentage of any development with 2 areas of slight interest.

Link
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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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