Why is the flu more common during the winter season?

December 13, 2012 by Lindsey A Haugh

(Medical Xpress)—Influenza, commonly known as the flu, has distinct transmission patterns around the world. In temperate regions, influenza's occurrence peaks during the winter season, while in some tropical regions, the disease's occurrence tends to correspond with the rainy season.

Linsey Marr, associate professor of civil and environmental engineering at Virginia Tech, and her colleagues, Wan Yang of Blacksburg, Va., one of her doctoral students, and Elankumaran Subbiah, a in the biomedical sciences and pathobiology department of the Virginia-Maryland Regional College of Veterinary Medicine, measured the influenza A virus survival rate at various levels of humidity.

Their study presents for the first time the relationship between the viability in human mucus and humidity over a large range of relative humidities, from 17 percent to 100 percent. They found the viability of the flu A virus was highest when the was either close to 100 percent or below 50 percent. The results in human mucus may help explain influenza's seasonality in different regions.

"We added to droplets of simulated respiratory fluid and to actual human mucus and then measured what fraction survived after exposure to low, medium, and high relative humidities," said Marr.

At low humidity, respiratory droplets evaporate completely and the virus survives well under dry conditions. But at moderate humidity, the droplets evaporate some, but not completely, leaving the virus exposed to higher levels of chemicals in the fluid and compromising the virus' ability to infect cells.

In a past study also conducted by Marr, Yang, and Subbiah, published in United Kingdom's Journal of the Royal Society Interface, the researchers collected samples from a waiting room of a health care center, two toddlers' rooms and one babies' area of a day care center, as well as three cross-country flights. Findings showed the average concentration was 16,000 viruses per cubic meter of air, and the majority of the viruses were associated with fine particles, less than 2.5 micrometers, which can remain suspended for hours.

Possible explanations for the seasonality of the flu have been investigated, such as the return of kids to school, people spending more time indoors in the winter, and lower light levels that affect the immune system, but there is no agreement on them, said the NSF CAREER award recipient.

The researchers found humidity could explain the of influenza by controlling the ability of viruses to remain infectious while they are in droplets or aerosols. The viruses survived best at low humidity, such as those found indoors in the winter, and at extremely high humidity. affects the composition of the fluid, namely the concentrations of salts and proteins in respiratory droplets, and this affects the of the flu virus.

More information: rsif.royalsocietypublishing.or … ntent/8/61/1176.full

Related Stories

Recommended for you

Google searches can be used to track dengue in underdeveloped countries

July 20, 2017
An analytical tool that combines Google search data with government-provided clinical data can quickly and accurately track dengue fever in less-developed countries, according to new research published in PLOS Computational ...

MRSA emerged years before methicillin was even discovered

July 19, 2017
Methicillin resistant Staphylococcus aureus (MRSA) emerged long before the introduction of the antibiotic methicillin into clinical practice, according to a study published in the open access journal Genome Biology. It was ...

New test distinguishes Zika from similar viral infections

July 18, 2017
A new test is the best-to-date in differentiating Zika virus infections from infections caused by similar viruses. The antibody-based assay, developed by researchers at UC Berkeley and Humabs BioMed, a private biotechnology ...

'Superbugs' study reveals complex picture of E. coli bloodstream infections

July 18, 2017
The first large-scale genetic study of Escherichia coli (E. coli) cultured from patients with bloodstream infections in England showed that drug resistant 'superbugs' are not always out-competing other strains. Research by ...

Ebola virus can persist in monkeys that survived disease, even after symptoms disappear

July 17, 2017
Ebola virus infection can be detected in rhesus monkeys that survive the disease and no longer show symptoms, according to research published by Army scientists in today's online edition of the journal Nature Microbiology. ...

Mountain gorillas have herpes virus similar to that found in humans

July 13, 2017
Scientists from the University of California, Davis, have detected a herpes virus in wild mountain gorillas that is very similar to the Epstein-Barr virus in humans, according to a study published today in the journal Scientific ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.