Influenza and the weather
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
Reader Comments
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Andrea in 07 was on the 9th.
It is 26 days, 4 hours, 57 minutes and 38 seconds until Monday, 1 June 2009, 00:00:01 (Praia time)...
Getting closer.
But here, just wish it would stop raining.
Have mine. It's also cold, like top 40s. It was mid 70s like 2-3 weeks ago.
I wasn't aware we suddenly shifted to the southern Hemisphere...
I'll try my best! May do a rain dance.
You know, with the economies as they are... missed a trick in not selling rain...
My father one time (a million years ago) did a rain dance after he had too many scotches...POURED that night! So the rain dance thing is always a thought. :)
Have a great night...go outside with your family and jump in puddles - at least have a good time with it!
Yes, have heard such stories before. Pretty sure Rob/Pottery succeeded once...
And been out in it all day. Got positively drenched.
*dances*?
Bad experience(s) with whiskey. Have to leave that one out...
TC ADVISORY
DTG: 20090505/1800Z
TCAC: TOKYO
TC: CHAN-HOM
NR: 11
PSN: N1320 E11220
MOV: NE 08KT
C: 975HPA
MAX WIND: 60KT
FCST PSN +6HR: 06/0000Z N1335 E11240
FCST MAX WIND +6HR: 65KT
FCST PSN +12HR: 06/0600Z N1350 E11310
FCST MAX WIND +12HR: 65KT
FCST PSN +18HR: 06/1200Z N1355 E11340
FCST MAX WIND +18HR: 65KT
FCST PSN +24HR: 06/1800Z N1400 E11405
FCST MAX WIND +24HR: 65KT
RMK: NIL
NXT MSG: 20090506/0000Z =
TCNA21 RJTD 051800 CCA
CCAA 05180 47644 KUJIRA(0901) 01196 11369 13114 255// 90716=
CHAN-HOM(0902) 03133 11123 13234 240// 90508=
18:00 PM UTC May 5
TY KUJIRA (0901)
19.6N 136.9E
Current Dvorak Intensity: T5.5
Strongest DT: T6.0 (May 5)
STS CHAN-HOM (0902)
13.3N 112.3E
Dvorak Intensity: T4.0
Tropical Cyclone Advisory #25
TYPHOON KUJIRA (CAT 3)
3:00 AM JST May 6 2009
================================
Subject: Category Three Cyclone In Sea East Of The Philippines
At 18:00 PM UTC, Typhoon Kujira (950 hPa) located at 19.5N 136.9E has 10 minute sustained winds of 75 knots with gusts of 105 knots. The typhoon is reported as moving east-northeast at 15 knots.
Dvorak Intensity: T5.5
Storm Force Winds
=================
60 NM from the center
Gale Force Winds
===============
150 NM from the center
Forecast and Intensity
=======================
24 HRS: 23.9N 141.1E - 65 knots (CAT 3/Typhoon)
48 HRS: 30.2N 145.5E - 45 knots (CAT 1/Tropical Storm)
72 HRS: 38.6N 153.5E - EXTRATROPICAL
Unfortunately too many people have bad experiences with it, so to hear that.
Tropical Cyclone Advisory #20
SEVERE TROPICAL STORM CHAN-HOM (CAT 2)
3:00 AM JST May 6 2009
================================
Subject: Category Two Cyclone In The South China Sea
At 18:00 PM UTC, Severe Tropical Storm Chan-Hom (975 hPa) located at 13.3N 112.3E has 10 minute sustained winds of 60 knots with gusts of 85 knots. The storm is reported as moving northeast at 8 knots.
Dvorak Intensity: T4.0
Storm-Force Winds
==================
50 NM from the center
Gale-Force Winds
===============
140 NM from the center
Forecast and Intensity
=======================
24 HRS: 14.0N 114.1E - 65 knots (CAT 3/Typhoon)
48 HRS: 15.2N 116.6E - 60 knots (CAT 2/Severe Tropical Storm)
72 HRS: 16.4N 118.9E - 60 knots (CAT 2/Severe Tropical Storm)
KEH - washing your car is a SURE bet it will rain...always works for me. I should have thought of that!
For me its planning an outdoor cookout,never fails
Or just a coincidence the location is the same as the upper level low ~28N 73W?
It's not a "possible" relo anymore - hubby got the job and he's already there. Bought a house in San Diego and now we're trying to unload the one here. Kids get out of school on May 22 - hopefully as soon as the house closes in San Diego, we are on the road!!! Hopefully it's before hurricane season starts in full.
How's by you?
Still waiting for the rain here...think it's going to swoop north again
NATIONAL WEATHER SERVICE RALEIGH NC
602 PM EDT TUE MAY 5 2009
NCC127-195-052215-
/O.CON.KRAH.TO.W.0015.000000T0000Z-090505T2215Z/
WILSON NC-NASH NC-
602 PM EDT TUE MAY 5 2009
...A TORNADO WARNING REMAINS IN EFFECT UNTIL 615 PM EDT FOR NASH AND
NORTHWESTERN WILSON COUNTIES...
AT 600 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR CONTINUED TO
INDICATE A TORNADO. THIS TORNADO WAS LOCATED NEAR BAILEY...OR 14
MILES EAST OF LINWOOD...MOVING NORTHEAST AT 25 MPH.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
THIS TORNADO HAS A HISTORY OF PRODUCING MAJOR DAMAGE IN NORTHEAST
JOHNSTON COUNTY. THIS IS AN EXTREMELY DANGEROUS SITUATION! TAKE
COVER NOW! IF YOU WAIT TO SEE OR HEAR IT COMING...IT MAY BE TOO
LATE TO GET TO A SAFE PLACE.
A TORNADO WATCH REMAINS IN EFFECT UNTIL MIDNIGHT EDT WEDNESDAY
MORNING FOR CENTRAL NORTH CAROLINA.
----
wow
NATIONAL WEATHER SERVICE RALEIGH NC
613 PM EDT TUE MAY 5 2009
NCC065-127-195-052245-
/O.CON.KRAH.TO.W.0017.000000T0000Z-090505T2245Z/
WILSON NC-EDGECOMBE NC-NASH NC-
613 PM EDT TUE MAY 5 2009
...A TORNADO WARNING REMAINS IN EFFECT UNTIL 645 PM EDT FOR SOUTHERN
NASH...NORTHWESTERN EDGECOMBE AND NORTHWESTERN WILSON COUNTIES...
AT 608 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR CONTINUED TO
INDICATE A TORNADO. THIS TORNADO WAS LOCATED ABOUT 5 MILES
NORTHEAST OF SIMS...OR 12 MILES SOUTH OF NASHVILLE...MOVING
NORTHEAST AT 20 MPH. THE TORNADO WILL CROSS INTERSTATE 95 BY 620 PM!
PRECAUTIONARY/PREPAREDNESS ACTIONS...
THIS TORNADO HAS A HISTORY OF PRODUCING MAJOR DAMAGE IN NORTHEAST
JOHNSTON COUNTY. THIS IS AN EXTREMELY DANGEROUS SITUATION! TAKE
COVER NOW! IF YOU WAIT TO SEE OR HEAR IT COMING...IT MAY BE TOO
LATE TO GET TO A SAFE PLACE. DO NOT USE HIGHWAY OVERPASSES FOR
SHELTER. OVERPASSES DO NOT PROVIDE PROTECTION FROM TORNADIC WINDS.
VEHICLES STOPPED UNDER BRIDGES BLOCK TRAFFIC AND PREVENT PEOPLE FROM
GETTING OUT OF THE STORM`S PATH AND TO SHELTER. IF YOU CANNOT DRIVE
AWAY FROM THE TORNADO...GET OUT OF YOUR VEHICLE AND LIE FLAT IN A
DITCH AS A LAST RESORT.
A TORNADO WATCH REMAINS IN EFFECT UNTIL MIDNIGHT EDT WEDNESDAY
MORNING FOR CENTRAL NORTH CAROLINA.
&&
LAT...LON 3611 7772 3589 7756 3572 7810 3583 7819
TIME...MOT...LOC 2212Z 239DEG 19KT 3582 7800
$$
VINCENT
----
hope it lifts before I-95
Were not looking for it to develop. Were just watching some possible waves roll off.
Are you refering to the convection, the wave axis extends over the continent.
Exactly.
Well during World War 2, Riehl proposed the idea of the easterly wave model. He got the name because he found that these disturbances (waves) often move towards the east, modulating weather across the Caribbean and cause a disturbance within the easterly trades.
Later, Frank proposed the inverted V pattern with the use of satellite imagery which showed the wave caused inverted v patterns within the cloud clusters along the ITCZ and across the Tropical Atlantic.
The source of these waves were not known until the 1980s and 1990s when the African Easterly jet was proposed which may also be a source of the name.
NRL is running two test Tropical Cyclones on their tracking maps labeled "EXERCISE EXERCISE EXERCISE". Pretty cool to see. Remember these are not real storms. Link
GOES-12 Atlantic Basin
History teaches that a lack of hurricane awareness and preparation are common threads among all major hurricane disasters. By knowing your vulnerability and what actions you should take, you can reduce the effects of a hurricane disaster.
Hurricane Preparedness Week during 2009 will be held May 24th through May 30th.
Cinnamon Girl,Sunday,Jazz fest NOLA
Hurricane.com since 1994,with more Cane Prep
Click Here
Can someone explain? She is going to be registering here for the first time and asking questions...perhaps someone can provide the info and what she should do...
Thank you, Melissa
I think this is the first area that you have speculated that I actually agree with based on my own observations.
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