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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Quoting RTLSNK:


Will send you a WU-mail.


Thanks.......
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Quoting TampaSpin:


Taz,
Not familiar with Tornodo's in Hawaii. Does that happen often. Never heard of it before...HUM!
it last happen in 2005 i think not that that means anything i have to check to confirm
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Galveston mayor learns hurricane prep lessons from Cubans
KHOU - ‎May 4, 2009‎

By Leigh Jones / The Daily News

GALVESTON, Texas — Mayor Lyda Ann Thomas said she wants island residents to take more responsibility for each other the next time a hurricane spins into the Gulf of Mexico.

During a four-day trip to Cuba, Thomas learned about the island nation’s “know your neighbor” program, where residents are expected to help the government keep track of who might need extra help during storm preparation and evacuation.
Member Since: July 3, 2005 Posts: 424 Comments: 128273
Quoting Tazmanian:
February 11 (Hawaii)

On February 11, two tornadoes touched down on Oahu in Hawaii. At 12:50 pm HST (2250 UTC), the first tornado touched down near a quarry, damaging nearby buildings. The tornado moved through a golf course next, throwing a utility cart about 50 to 60 feet. The tornado lifted at 1:10 pm HST (2310 UTC), 20 minutes after it touched down. Numerous trees were damaged throughout the tornado's mile long path.[24] An employee of the golf course was hospitalized for several hours after being blow into a glass window.[25] Following an assessment by the National Weather Service, the tornado was rated as an EF1.[24] During the assessment of the tornado, another weaker tornado was discovered to the northeast. The tornado touched down in a construction site and damaged dust barriers. The second tornado was on the ground for about ten minutes and traveled less than half a mile. The National Weather Service rated the tornado as a low-end EF0


Taz,
Not familiar with Tornodo's in Hawaii. Does that happen often. Never heard of it before...HUM!
Member Since: September 2, 2007 Posts: 178 Comments: 20439
Quoting weathermanwannabe:
Good Morning....Asked this yesterday but could not get it on with the instructions I received from someone.....How do I change my Avatar and put up a new picture?.....Thanks


Hey sorry if I gave you bad info. =)
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Quoting weathermanwannabe:
Good Morning....Asked this yesterday but could not get it on with the instructions I received from someone.....How do I change my Avatar and put up a new picture?.....Thanks


Will send you a WU-mail.
Member Since: September 3, 2008 Posts: 0 Comments: 20946
A major eruption is going to occur within the next 24hrs from Redoubt.

http://tampaspinsweather.webs.com/volcanoearthquakespace.htm
Member Since: September 2, 2007 Posts: 178 Comments: 20439
February 11 (Hawaii)

On February 11, two tornadoes touched down on Oahu in Hawaii. At 12:50 pm HST (2250 UTC), the first tornado touched down near a quarry, damaging nearby buildings. The tornado moved through a golf course next, throwing a utility cart about 50 to 60 feet. The tornado lifted at 1:10 pm HST (2310 UTC), 20 minutes after it touched down. Numerous trees were damaged throughout the tornado's mile long path.[24] An employee of the golf course was hospitalized for several hours after being blow into a glass window.[25] Following an assessment by the National Weather Service, the tornado was rated as an EF1.[24] During the assessment of the tornado, another weaker tornado was discovered to the northeast. The tornado touched down in a construction site and damaged dust barriers. The second tornado was on the ground for about ten minutes and traveled less than half a mile. The National Weather Service rated the tornado as a low-end EF0
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Good Morning....Asked this yesterday but could not get it on with the instructions I received from someone.....How do I change my Avatar and put up a new picture?.....Thanks
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Thanks Oz, have it bookmarked.
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Good Morning All:

I've been working very hard preparing for this upcoming hurricane season.

One of the projects you'll see this year is a new website. Here's the link to it.

As of today, there's limited functionality, so don't expect too much from it in the next two weeks. But over time...it should be a pretty cool site.

The biggest feature of the site is that it will be absolutely FREE. The second biggest feature will be the Current Hurricane Hunt link. I will be positioning a web cam on my mini-van along with a ProWeather Station that will stream real-time data to the site via WeatherUnderground.com and Stickam.com

Feel free to check it out and if you'd like, provide some feedback on what you think of the site and the idea behind it.

Till later then...

CycloneOz---
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We are entering a High MJO uplift period in the Atlantic. The next would make it about mid June - July 1st. That period could be very interesting for several developing systems.
Member Since: September 2, 2007 Posts: 178 Comments: 20439
Quoting Ossqss:
Health Officials Begin to Ease Public Alerts About Swine Flu


Swine Flu In Mexico,
Alert Staying Put


Why swine flu was news, and why it may be for a while


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.
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Quoting Orcasystems:


My money is on Strawberry rhubarb.


Orca....OH Hell yes....! My Favorite also....My father use to grow both in his garden and WOW! What a feast.
Member Since: September 2, 2007 Posts: 178 Comments: 20439
I don't like rhubarb lol. Ok back to work for a little.
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Quoting hahaguy:


Morning, I've actually had Blackberry cobbler once it was pretty good lol.


My money is on Strawberry rhubarb.
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Blog Refresh
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Quoting KEHCharleston:
72F This morning. Dew point 70F - Can we all say muggy!

50/50 chance of precip. Rain keeps sliding by to the north of us - not a good thing.

Blackberry cobbler is my very favorite - ya making me hungry Texan


Morning, I've actually had Blackberry cobbler once it was pretty good lol.
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thank you 456
yes the situation looks grave. i have been monitoring RFO radio out of martinique, and although the reports are a bit sketchy, there seems to be reports of drowning deaths.
i am in st lucia and it has been raning heavvily at times. there have been reports of minor landslides on the west coast. as i write it is very overcast with a moderate to light drizzle.
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Quoting Drakoen:
Nice cyclone in the Pacific:


Re #323 -- Anyone else see a face in that image?
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Quoting stoormfury:
morning
flooding rains in the island of martinique where overnight rains have floode homes and businesses in the capital fort de france. cars have been washed away and the fire sevices have had to rescue persons standed by the floods


Sounds bad down there. We aslo had a downpour here but that bad. Hope everthing is ok with you. Thoughts and prayers.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
72F This morning. Dew point 70F - Can we all say muggy!

50/50 chance of precip. Rain keeps sliding by to the north of us - not a good thing.

Quoting SomeRandomTexan:
later on Weather456

KEH yes a cobbler made with dewberries... which are very similar to blackberries... dewberries just become ripe before blackberries and grow on small cluster plants instead of extensive thorny vines..

utterly delightful tasting
Blackberry cobbler is my very favorite - ya making me hungry Texan
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Link
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radar out of martinique this morning
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Tropical update
Member Since: July 24, 2005 Posts: 407 Comments: 19076
morning
flooding rains in the island of martinique where overnight rains have floode homes and businesses in the capital fort de france. cars have been washed away and the fire sevices have had to rescue persons standed by the floods
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The water temps are lower than last year at this time in Florida
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.
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For those who are newbies to forecasting, and those who want to brush up on forecasting skills, I wrote a hurricane forecasting tutorial last season on my current blog. JFYI....=)
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check this out:I believe the black line is 80*F and its creeping north quickly!!!,our local water temp just hit 80 today here in sarasota and let me tell you with how strong the FL sun is,it feels great!!!!
the bottom one is the 5 day temp change
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I know y'all want to talk about tropical weather even if it is occuring in other hemispheres...haha, no really...the current flu blog is still fascinating reading.
And here's more:
http://www.cdc.gov/ncidod/eid/vol12no01/05-0979.htm

Link
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Quoting Ossqss:


Nope, didn't find that one in the search results below.

Acronym Definition
AMEN Arlingtonians Meeting Emergency Needs, Inc (formerly Arlingtonians Ministering to Emergency Needs, Inc.)
AMEN Association of Medical Esthetic Nurses
AMEN Anacostia Men's Employment Network
AMEN Area Ministry for Emergency Needs
AMEN Arlingtonians Ministering to Emergency Needs, Inc.
AMEN Advanced Manufacturing Education Network
AMEN Alabama Micro Enterprise Network
AMEN Applied Mathematics E-Note
AMEN Aviation Maintenance Engineering Analysis System
AMEN Aksie Mobilisering En Nasorg


But think this one fits with the history behind it.

Anonymous,Misfit,Emitting,Nonsense

Just my take on the way out - CUL8R :)



Well done ;)
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Storm and Drak---
Nice Images... it could be the one!
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Doc,

We love your blog and your nsights. But the TDWR radars on the main radar site are garbage on their best day. Their resolution, on any adjustment, is poor, and the best thing they are suited for is magnifying the ground clutter so that no other reflections are visible. Might I suggest two radar sites - one TDWR and one regular?

Thanks
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We'll see if this becomes the first AEW of the 2009 season.



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Quoting help4u:
AMEN!!Apocalypse-induced Environmental nervousness!!!


Nope, didn't find that one in the search results below.

Acronym Definition
AMEN Arlingtonians Meeting Emergency Needs, Inc (formerly Arlingtonians Ministering to Emergency Needs, Inc.)
AMEN Association of Medical Esthetic Nurses
AMEN Anacostia Men's Employment Network
AMEN Area Ministry for Emergency Needs
AMEN Arlingtonians Ministering to Emergency Needs, Inc.
AMEN Advanced Manufacturing Education Network
AMEN Alabama Micro Enterprise Network
AMEN Applied Mathematics E-Note
AMEN Aviation Maintenance Engineering Analysis System
AMEN Aksie Mobilisering En Nasorg


But think this one fits with the history behind it.

Anonymous,Misfit,Emitting,Nonsense

Just my take on the way out - CUL8R :)

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AMEN!!Apocalypse-induced Environmental nervousness!!!
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Ok, I give up. I cannot find the longer loop. I am surprised that no one found the item among us. It was interesting to see two spining blobs that close to each other. Granted, it was not long lived. Have a happy all - L8R
Member Since: June 12, 2005 Posts: 6 Comments: 8186
CHAN-HOM

http://www.nrlmry.navy.mil/tc-bin/tc_home2.cgi?ACTIVES=09-WPAC-01W.KUJIRA,09-WPAC-02W.CHAN-HOM,09-W PAC-95W.INVEST&PHOT=yes&ATCF_BASIN=wp&SUB_PROD=1km&SIZE=Thumb&NAV=tc&YR=09&ATCF_YR=2009&YEAR=2009&AT CF_FILE=/SATPRODUCTS/kauai_data/www/atcf_web/public_html/image_archives/2009/wp022009.09050418.gif&C URRENT=20090505.0130.gms6.x.ir1km.02WCHAN-HOM.55kts-982mb-116N-1120E.100pc.jpg&AGE=Latest&CURRENT_AT CF=wp022009.09050418.gif&ATCF_NAME=wp022009&ATCF_DIR=/SATPRODUCTS/kauai_data/www/atcf_web/public_htm l/image_archives/2009&ARCHIVE=active&MO=MAY&BASIN=WPAC&AREA=pacific/southern_hemisphere&STORM_NAME=0 2W.CHAN-HOM&STYLE=tables&PROD=ir&TYPE=ssmi&DIR=/SATPRODUCTS/TC/tc09/WPAC/02W.CHAN-HOM/ir/geo/1km&USE _THIS_DIR=/SATPRODUCTS/TC/tc09/WPAC/02W.CHAN-HOM/ssmi/scat&ANIM_TYPE=Instant

wasn't able to post as a link
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area of disturb weather


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later on Weather456

KEH yes a cobbler made with dewberries... which are very similar to blackberries... dewberries just become ripe before blackberries and grow on small cluster plants instead of extensive thorny vines..

utterly delightful tasting
Member Since: August 30, 2007 Posts: 0 Comments: 1857
Quoting Weather456:
339. AussieStorm 10:11 PM AST on May 04, 2009

The comment was referring to the one near Vietnam



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Quoting SomeRandomTexan:
Hey Aussie! Hows is everything over there in Australia ?

Weather in Sydney there past few days....
'Mini-tornado' dumps caravan in lagoon
Saturday May 2, 2009

Police say three women have been injured when a water funnel or mini-tornado lifted a caravan on the New South Wales central coast on Saturday afternoon.

Officers say the mini-tornado tore through a caravan park at The Entrance about 3:00pm and dumped one of the caravans in a nearby lagoon.

Three women staying at the park have been taken to Gosford Hospital, one with a broken arm and the others with cuts and bruises.

And

Storms flirt with the Sydney coastline
Martin Palmer, Sunday May 3, 2009

On Saturday storms battered parts of eastern Sydney whilst much of the rest of the city remained almost bone dry.

The bright sunny skies of Saturday morning lulled many into leaving their umbrellas at home, indeed there was little evidence of the upper trough lingering ominously offshore. As things warmed up however and the trough moved landward, clouds began to build signaling that something may be afoot.

By 2.30pm clusters of storms began sparking offshore, one south of Wollongong and another just out from The Entrance. By 3pm rain was falling along parts of the coast and a tornado had struck The Entrance.

It wasn't until about 7.30pm that the storms really began to move inshore. Over the next few hours most Sydneysiders were treated to an impressive lightning show, although those in the eastern suburbs would have been diving for shelter as heavy rain moved in.

In the subsequent hours to 9am on Sunday Randwick collected 77mm, their highest May total in 35 years. Mona Vale hit 57mm, Avalon 44mm, Bondi 41mm, yet the city only saw 13mm. The storms made little progress inland and anywhere west of Canterbury saw no rain whatsoever.

- Weatherzone
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Have a good night all
Member Since: July 24, 2005 Posts: 407 Comments: 19076

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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.