Featured Research

from universities, journals, and other organizations

Dry winters linked to seasonal outbreaks of influenza

Date:
February 23, 2010
Source:
Public Library of Science
Summary:
The seasonal increase of influenza has long baffled scientists, but a new study has found that seasonal changes of absolute humidity are the apparent underlying cause of these wintertime peaks. The study also found that the onset of outbreaks might be encouraged by anomalously dry weather conditions, at least in temperate regions.

The seasonal increase of influenza has long baffled scientists, but a new study published in PLoS Biology has found that seasonal changes of absolute humidity are the apparent underlying cause of these wintertime peaks. The study also found that the onset of outbreaks might be encouraged by anomalously dry weather conditions, at least in temperate regions.

Scientists have long suspected a link between humidity and seasonal (epidemic) flu outbreaks, but most of the research has focused on relative humidity -- the ratio of water vapor content in the air to the saturating level, which varies with temperature. Absolute humidity quantifies the actual amount of water in the air, irrespective of temperature. Though somewhat counter-intuitive, absolute humidity is much higher in the summer. "In some areas of the country, a typical summer day can have four times as much water vapor as a typical winter day -- a difference that exists both indoors and outdoors," said Jeffrey Shaman, an Oregon State University atmospheric scientist and lead author.

The researchers used 31 years of observed absolute humidity conditions to drive a mathematical model of influenza and found that the model simulations reproduced the observed seasonal cycle of influenza throughout the United States. They first examined influenza in New York, Washington, Illinois, Arizona and Florida, and found that the absolute humidity conditions in those states all produced model-simulated seasonal outbreaks of influenza that correlated well with the observed seasonal cycle of influenza within each state. Shaman and colleagues then extended their model to the rest of the continental U.S. and were able to reproduce the seasonal cycle of influenza elsewhere. They also discovered that the start of many influenza outbreaks during the winter was directly preceded by a period of weather that was drier than usual.

"This dry period is not a requirement for triggering an influenza outbreak, but it was present in 55 to 60 percent of the outbreaks we analyzed so it appears to increase the likelihood of an outbreak," said Shaman. "The virus response is almost immediate; transmission and survival rates increase and about 10 days later, the observed influenza mortality rates follow."

Though the findings by Shaman and his colleagues build a strong case for absolute humidity's role in influenza outbreaks, it does not mean you can predict where influenza will strike next. As Shaman emphasized, "Certainly absolute humidity may affect the survival of the influenza virus, but the severity of outbreaks is also dependent upon other variables, including the type of virus and its virulence, as well as host-mediated factors such as the susceptibility of a population and rates of population mixing and person-to-person interactions."

Marc Lipsitch, a professor of epidemiology at the Harvard School of Public Health and senior author on the new study, said the new analysis may have implications for other diseases. "Seasonality of infectious diseases is one of the oldest observations in human health, but the mechanisms -- especially for respiratory diseases like flu -- have been unclear," Lipsitch said. "This study, in combination with Shaman and (Melvin) Kohn's earlier analysis of laboratory experiments on flu transmission, points to variation in humidity as a major cause of seasonal cycles in flu."

"Seasonal variation in flu, in turn, helps to explain variation in other infectious diseases -- such as pneumococcal and meningococcal disease -- as well as seasonal variation in heart attacks, strokes and other important health outcomes."

Lipsitch directs the Center for Communicable Disease Dynamics, of which Shaman is a member. This study and the center are supported by the Models of Infectious Disease Agent Study, or "MIDAS Program," of the U.S. National Institute of General Medical Sciences.

"The discovery of a link between influenza outbreaks and absolute humidity could have a major impact on the development of strategies for limiting the spread of infection," said Irene Eckstrand, who oversees the MIDAS program. "Understanding why outbreaks arise is an important first step toward containing or even preventing them, so it is essential for scientists to follow up on this intriguing connection."

Additional collaborators on the study published in PLoS Biology were Virginia Pitzer and Bryan Grenfell, Princeton University; and Cecile Viboud, National Institutes of Health, Fogarty International Center. The study builds on previous laboratory research that found influenza virus survival rates increased greatly as absolute humidity decreased.

This work was supported, in part, by the US National Institutes of Health (NIH) Models of Infectious Disease Agent Study program through cooperative agreements 5U01GM076497 (ML) and 1U54GM088588 (ML and JS). VEP and BG were supported by NIH grant R01GM083983-01, the Bill and Melinda Gates Foundation, the RAPIDD program of the Science and Technology Directorate, US Department of Homeland Security, and the Fogarty International Center, NIH.


Story Source:

The above story is based on materials provided by Public Library of Science. Note: Materials may be edited for content and length.


Journal Reference:

  1. Shaman et al. Absolute Humidity and the Seasonal Onset of Influenza in the Continental United States. PLoS Biology, 2010; 8 (2): e1000316 DOI: 10.1371/journal.pbio.1000316

Cite This Page:

Public Library of Science. "Dry winters linked to seasonal outbreaks of influenza." ScienceDaily. ScienceDaily, 23 February 2010. <www.sciencedaily.com/releases/2010/02/100222200847.htm>.
Public Library of Science. (2010, February 23). Dry winters linked to seasonal outbreaks of influenza. ScienceDaily. Retrieved July 31, 2014 from www.sciencedaily.com/releases/2010/02/100222200847.htm
Public Library of Science. "Dry winters linked to seasonal outbreaks of influenza." ScienceDaily. www.sciencedaily.com/releases/2010/02/100222200847.htm (accessed July 31, 2014).

Share This




More Health & Medicine News

Thursday, July 31, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Health Insurers' Profits Slide

Health Insurers' Profits Slide

Reuters - Business Video Online (July 30, 2014) Obamacare-related costs were said to be behind the profit plunge at Wellpoint and Humana, but Wellpoint sees the new exchanges boosting its earnings for the full year. Fred Katayama reports. Video provided by Reuters
Powered by NewsLook.com
Concern Grows Over Worsening Ebola Crisis

Concern Grows Over Worsening Ebola Crisis

AFP (July 30, 2014) Pan-African airline ASKY has suspended all flights to and from the capitals of Liberia and Sierra Leone amid the worsening Ebola health crisis, which has so far caused 672 deaths in Guinea, Liberia and Sierra Leone. Duration: 00:43 Video provided by AFP
Powered by NewsLook.com
At Least 20 Chikungunya Cases in New Jersey

At Least 20 Chikungunya Cases in New Jersey

AP (July 30, 2014) At least 20 New Jersey residents have tested positive for chikungunya, a mosquito-borne virus that has spread through the Caribbean. (July 30) Video provided by AP
Powered by NewsLook.com
Xtreme Eating: Your Daily Caloric Intake All On One Plate

Xtreme Eating: Your Daily Caloric Intake All On One Plate

Newsy (July 30, 2014) The Center for Science in the Public Interest released its 2014 list of single meals with whopping calorie counts. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

    Environment News

    Technology News



      Save/Print:
      Share:

      Free Subscriptions


      Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

      Get Social & Mobile


      Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

      Have Feedback?


      Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
      Mobile: iPhone Android Web
      Follow: Facebook Twitter Google+
      Subscribe: RSS Feeds Email Newsletters
      Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins