There's A Crowd Of Reasons We Get The Flu In Winter

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There's a crowd of reasons we get the flu in winter

By Kim Painter

USA TODAY

01-13-2008

 

If it's mid-January (and it is), it must be flu season.

But why do winter and the flu go together? The one-word explanation

most people have heard: crowding.

 

That is, in winter people crowd together inside, providing a perfect

opportunity for flu viruses and other respiratory infections to

spread. But scientists and common-sense thinkers alike have been

questioning the so-called crowding theory for years.

 

" We have schools in May and June, and people do get together at movie

theaters in the summer, " says Peter Palese, chairman of the

microbiology department at Mount Sinai School of Medicine in New

York. " Crowding alone doesn't explain it. "

 

Alternative theories abound. Some center on how the human body

responds to decreased sunlight — by making less of the hormone

melatonin or vitamin D, for example, both of which might affect

immunity.

 

Another theory is that drier, colder air is key. A recent study by

Palese and his colleagues gave the strongest support yet to that

idea. The scientists exposed guinea pigs to flu viruses and found

they easily infected one another in cool, dry air but couldn't spread

the flu at all at 30 degrees Celsius (86 F).

 

So, should we all just turn our houses (and nursing homes and

schools) into saunas and invite in the neighbors?

 

No. For one thing, what's bad for the flu virus may be perfect for

other microbes: Molds and bacteria would be delighted to take up

residence in overheated, highly humidified buildings, Palese

says. " We have to be very careful about any sort of public health

recommendation, " he says.

 

Meanwhile, health experts say that even if crowding is not the

primary cause of seasonal flu patterns, it still plays a role in

spreading flu when it is afoot. Other illnesses, including the common

cold, also love a crowd. That's true even though the microbes that

cause various illnesses spread in different ways, with common cold

viruses thriving on direct contact, like hand-shaking, but flu

viruses spreading mostly through droplets in the air.

 

In fact, even before people knew about viruses and bacteria, they

understood that certain illnesses — from colds and flus to TB and

smallpox — spread from person to person, and called them " crowding

diseases, " says Howard Markel, director of the Center for the History

of Medicine at the University of Michigan.

 

" It's common sense that the more crowded a situation is, the more at

risk you are, " Markel says.

 

" Crowding is bad, independent of everything else, " says Dean Erdman,

a respiratory-virus researcher at the federal Centers for Disease

Control and Prevention.

 

Cold researcher Ronald Turner of the University of Virginia

agrees: " At the extreme, if you avoid all contact with other

individuals, you won't get infected. "

 

But is a child more likely to get sick in a classroom of 30 children

than a classroom of 20? Is there an ideal distance to maintain

between yourself and others in a crowd? Could a severe flu pandemic

be slowed by shutting down schools and workplaces and prohibiting

other public gatherings?

 

Answers to such questions are sparse and often based on conjecture.

But interest in the answers is growing as health experts plan for

pandemic flu and other emerging infections.

 

One thing researchers do know, Erdman says, is that some germs are

especially well-adapted to crowded conditions. Among them are

adenoviruses, which often cause outbreaks of respiratory illnesses

among military recruits. One apparently nasty strain is implicated in

recent severe cases of the so-called boot camp flu.

 

But the most promising potential solution, Erdman says, isn't private

rooms for recruits; it's a vaccine the military hopes to reintroduce

soon. Likewise, the best way to avoid garden-variety influenza is to

get a flu vaccine, Palese says.

 

There's no vaccine for the cold, but — short of locking yourself in a

closet — Turner says that " washing your hands continues to be the

best thing we have to offer. "

 

Find this article at:

http://www.usatoday.com/news/health/painter/2008-01-13-winter-flu-

crowds_N.htm

 

Copyright 2008 USA TODAY, a division of Gannett Co. Inc.