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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Here is my Analysis and Percentage of any development with 2 areas of slight interest.

Link
Member Since: September 2, 2007 Posts: 179 Comments: 20448
To add to what I just wrote, if I was to forecast down to the very microscale process(ie:evaporation, condensation, small segments of the atmosphere, etc)for that given tiny area, it gets so complicated, even computer model equations wont be able to ascertain the micro physics well...
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Quoting TampaSpin:


Not sure i agree with what i put in bold. I think the smaller the area the easier it would be to forecast.


Its highly complex, which is why anyone could find an example to counter what I said(If the overall pattern in the area was stagnant, then I could say that a localized forecast was more certain under that scenario). When you decrease the area forecasted, in general, forecasts will often be more uncertain. If I were to forecast rain for a 2 mile stretch of interstate and forecast rain for an entire county, the bigger area has a greater chance that my forecast holds true. When it comes to shear, it is often times very difficult to forecast with any degree of skill more than a week out because shear maps show shear averaged over 2 layers...And much of it is estimation over the open oceans...
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641. HadesGodWyvern (Mod)
Philippines Atmospherical Geophysical Astronomical Services and Administration

Special Tropical Weather Advisory
==================================
The Tropical Storm (International Name: Chan-hom) located west of southern Luzon was estimated 710 kms west of Mindoro (13.5N 113.0E) with maximum sustained winds of 110 km/h (55 knots) with gustiness up to 140 km/h (75 knots). It is forecasted to move northeast at 7 knots. This weather disturbance is expected to enter over the western boundary of Philippine Area of Responsibility by tomorrow morning. This tropical cyclone is still far away to affect any parts of the country.

The active intertropical convergence zone will bring scattered rain showers and thunderstorms over northern and central Luzon becoming widespread over the western sections which may trigger flash flooding.

Residents in these areas are advised to take all the necessary precautionary measures.

The next update will be incorporated in the regular public weather forecast to tbe issued at 5:00 PM PhST today.
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640. Skyepony (Mod)
What is with this quikscat pass? Usually just 1 wide swath of where it is right now missing. Tonight there is 2. Oh wait the one over Africa looks fine north of Africa. Even a few wind barbs below. Missing right where I came to see.



Check out around 5N25W

That fire in Palm Bay is contained. Fences were lost but they did good. That fire was running between houses.


Member Since: August 10, 2005 Posts: 226 Comments: 39441
Well,
At least we know what caused the "Swine Flu" Outbreak...

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Quoting Drakoen:


I think this is the first area that you have speculated that I actually agree with based on my own observations.


I mentioned last night that I thought this area might be our first T-wave,if it holds over water,it will be!!!!
Member Since: October 5, 2007 Posts: 20 Comments: 4970
I haven't seen anyone post anything about this, but eastern North Carolina had tornadoes today that caused some pretty heavy damage. I found this website that has some pictures.

Link
Member Since: April 26, 2009 Posts: 3 Comments: 3667
Quoting quasigeostropic:
I guess the better question is how accurately shear can be forecasted in that time period.

As a general rule, the larger the area forecasted, the lower the uncertainty and as time increases, uncertainty increases. For example, forecasting shear for a localized area can be much more uncertain, than forecasting a bigger area. Another thing to keep in mind is forecasting shear over the open ocean(ie:middle of Atl.)and over land....Near land-->more data resources, over remote areas of ocean--->less data resources...So, in general, the more weather data, the more certain the forecast...


Not sure i agree with what i put in bold. I think the smaller the area the easier it would be to forecast.
Member Since: September 2, 2007 Posts: 179 Comments: 20448
I guess the better question is how accurately shear can be forecasted in that time period.

As a general rule, the larger the area forecasted, the lower the uncertainty and as time increases, uncertainty increases. For example, forecasting shear for a localized area can be much more uncertain, than forecasting a bigger area. Another thing to keep in mind is forecasting shear over the open ocean(ie:middle of Atl.)and over land....Near land-->more data resources, over remote areas of ocean--->less data resources...So, in general, the more weather data, the more certain the forecast...
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Quoting JRRP:


Interesting to watch the African continent weather energy follow the Sun North.

As we move towards Solstice, I should note. L8R
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NHC Tropical Cyclone Model Output Maps

This page displays National Hurricane Center (NHC) model output of all model-projected tracks and intensities for any "invest" areas or classified tropical cyclones in the Atlantic, East Pacific, and Central Pacific basins. These plots are created using the GrADS software package and the NHC ATCF data feed available from ftp://ftp.tpc.ncep.noaa.gov/atcf/aid_public/. Both current and archived plots may be accessed using the menus that are available for each active storm below.
Member Since: July 3, 2005 Posts: 428 Comments: 129903

Tropical RAMSDIS Online


Both the new and old versions are being updated for now. You may access the old version at the following link: http://www1.cira.colostate.edu/ramm/rmsdsol/TROPICAL.html
Member Since: July 3, 2005 Posts: 428 Comments: 129903
631. JRRP
Member Since: August 16, 2007 Posts: 0 Comments: 6213
It was a good day today. The RAYS won and the Yanks got beat! Dam Sox won also tho.
Member Since: September 2, 2007 Posts: 179 Comments: 20448
Quoting Drakoen:


I guess the better question is how accurately shear can be forecasted in that time period.



Thanks for the sentiment...I think...


Anything derogatory was with tongue firmly planted in cheek.

Cheers.

Oh, and KC, turn emagdnim backwards.
Member Since: August 16, 2007 Posts: 6 Comments: 12463
Quoting KEEPEROFTHEGATE:
hamilton ?


Or Kitchener would be my guesses

I wonder if we get Wayne back?

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Quoting quasigeostropic:
The GFS is the best (I consider) at forecasting shear. Shear can be forecasted months in advance.

Shear forecasting has gotten better, and yes, a general shear pattern for a large area can be forecasted months in advance with a degree of uncertainty.


I guess the better question is how accurately shear can be forecasted in that time period.

Quoting atmoaggie:
A flyby:

Sheesh, Darkone. How did you end up with so many fans? And sometimes they just appear and bash you for their very first post.

You must have really been a bully in that middle school. These folks are driven by something.

And yet, whenever the question of met degrees comes up, most are surprised you are primarily self-taught, well-self-taught at that.

I concur with your GFS-favoring shear forecast worthiness statement, btw.

Today's sqeal-like-peewee's-playhouse word of the day: emagdnim

Later.


Thanks for the sentiment...I think...
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Sorry the Rain news for ya isnt better Chicklit .
Member Since: July 3, 2005 Posts: 428 Comments: 129903
hamilton ?
Member Since: July 15, 2006 Posts: 178 Comments: 56141
Still hoping the rain makes it to Charleston, tonight.

G'night folks

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Yeah, just what I thought Patrap...no sign of rain.
Evidently flu outbreaks occur about every 50 years and the last one was in 1968!
Good Wikipedia entry on 2009 H1N1 outbreak.
Link
goodnight
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Quoting SevereHurricane:
This seems like it happened forever ago.
But this only happened last year.
Who could go for Round 2?


I was in fort meyers for Fay. My first run in with a full blooded tropical cyclone...I enjoyed it. Not saying that Fay was good or anything, but it was exciting.
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Quoting Patrap:
Redoubt is Far too North and too small a Volcano to produce a significant cooling event even if it were to erupt violently.

Its the Pacific equatorial Big ones,Like Pinatubo,Krakatoa and the like that we worry about .


Your correct but, some of the fallout is now in the Atlantic now that could reduce some of heat as sunlight is reflected.
Member Since: September 2, 2007 Posts: 179 Comments: 20448
Quoting KEEPEROFTHEGATE:
take a shot give a shot do a little dance


I hear you may get a real Hockey team very very soon :)
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Linkie Dinkies are my forte, and now is the time to Bookmark and save the good uns fer the Season,..

Im not a Met,nor do I play one on TV.





Thanx, too
Member Since: July 3, 2005 Posts: 428 Comments: 129903
Patrap - Thanks for the links.
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Local Met just said the daily Showers will start next week he thought. He's probably correct with this heat and humidity!
Member Since: September 2, 2007 Posts: 179 Comments: 20448
Redoubt is Far too North and too small a Volcano to produce a significant cooling event even if it were to erupt violently.

Its the Pacific equatorial Big ones,Like Pinatubo,Krakatoa and the like that we worry about .
Member Since: July 3, 2005 Posts: 428 Comments: 129903
Quoting Ossqss:
Tampa, Tonga has been pinging again today in referece to the Redoubt item.

Link


I think your on to something......definitely a corelation between the two.
Member Since: September 2, 2007 Posts: 179 Comments: 20448
Should call it a night, but between watching Redoubt let off steam, and checking on the baby koi (which are too cute) - just too busy to call it quits yet.

Are any of you watching Redoubt? Steam is still being carried away in a horizontal line. In a full blown eruption, the plume would go straight up, right?
If Redoubt blows, and causes a bit of global cooling, will H1N1 activity increase, ya think?
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608
Right now.
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Tampa, Tonga has been pinging again today in reference to the Redoubt item.

Link
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Quoting Chicklit:
Good evening weatherfolk...anyone venture a guess about when we're going to get some rain in Florida?!


Miami 5-day forecast,wunderground


UNYSIS
GFSx 10-day Model
Member Since: July 3, 2005 Posts: 428 Comments: 129903
This seems like it happened forever ago.
But this only happened last year.
Who could go for Round 2?
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Models for Hurricanes and Weather
Tropical Cyclone Model Forecasts
Member Since: July 3, 2005 Posts: 428 Comments: 129903
Good evening weatherfolk...anyone venture a guess about when we're going to get some rain in Florida?!
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I predict no serious rain before 18th May in S. FL. based on climatology and the few maps I've looked at since Sat.

BTW, isn't the MJO supposed to be wet in our area over the next two weeks or so?

'Night to all. . .
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Quoting futuremet:


I'm dying for that right now

It is too dry here


Im sure the people who had their homes damaged from Hurricane Force winds aren't dying for it to happen.
But hey,
You need the rain!
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AN OVERVIEW OF NHC PREDICTION MODELS

Bernard N. Meisner
Scientific Services Division
National Weather Service Southern Region
Member Since: July 3, 2005 Posts: 428 Comments: 129903
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.

There will always be pros and cons for a warmer or colder climate. It is well known that colder weather makes people more prone to sickness because the body spends most its time trying to keep the body warm, and that distraction can allow for bacteria to enter into the body easier. Too hot, and one can have a heatstroke and die or as you stated, more disease carrying mosquitoes,etc. Now, to attribute most of the deaths to mere "heat" or "cold" is a bit misleading though. There are many other factors in each human that may make one more prone to sickness or less prone. It really is much more complex than a simplistic statement that "heat" will annihilate the planet....just my 2 cents...
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Quoting presslord:


well...actually...you, orca and Tampa are OK by me...which really doesn't speak so well for y'all...


I am not sure if I feel insulated, emancipated or detonated (®¿®) but I am good with either. :P

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Today's sqeal-like-peewee's-playhouse word of the day: emagdnim ???? Or should I ask?
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take a shot give a shot do a little dance
Member Since: July 15, 2006 Posts: 178 Comments: 56141
A flyby:

Sheesh, Darkone. How did you end up with so many fans? And sometimes they just appear and bash you for their very first post.

You must have really been a bully in that middle school. These folks are driven by something.

And yet, whenever the question of met degrees comes up, most are surprised you are primarily self-taught, well-self-taught at that.

I concur with your GFS-favoring shear forecast worthiness statement, btw.

Today's sqeal-like-peewee's-playhouse word of the day: emagdnim

Later.
Member Since: August 16, 2007 Posts: 6 Comments: 12463
Quoting conchygirl:
Orca - you trouble maker! :)


ummm and the new thing would be??
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3-1 Canucks.. final score
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Why northwest of Jamaica on May 23, you ask? (Well, I will pretend you asked)

Just do not see anything developing (other than wave) from Africa. Blobs too low, dust has not settled, shear too great.
I liked the area east and west of the Antilles, but just too much dust there, as well.
Decided on north of Jamaica, Antilles - no dust, water warming and shear may be conducive.

May 23 is my sisters Birthday.
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SPECIAL TROLL STATEMENT
NATIONAL TROLL SERVICE TROLL LAND
1030 PM EDT TUE MAY 5 2009

A TROLL WATCH ISSUED
TROLL SPOTTER REPORTS ARE COMING IN ON POSSIBLE TROLLS
NO FURTHER ACTION REQUIRER AT THIS TIME
Member Since: July 15, 2006 Posts: 178 Comments: 56141
Orca - you trouble maker! :)
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Quoting presslord:


well...actually...you, orca and Tampa are OK by me...which really doesn't speak so well for y'all...


Presslord you must be a Troll also with those kind words........LOL
Member Since: September 2, 2007 Posts: 179 Comments: 20448

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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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