Recent studies are shedding light on how cold and flu viruses develop across the United States. If you get sick this winter, you're in good company. Every year, Americans report more than 1 billion colds and miss more than 50 million workdays along with 60 million schooldays1. However, as we learn more about how these germs survive and are spread, we may be able to anticipate and hopefully divert this yearly germ migration, reducing the amount of sick days we need, and more importantly, save lives.
The Geography of Colds
In the United States, the official "cold season" begins in late August when the number of reported cold and flu illnesses rises sharply and remains elevated until late April or early May, when the number drops back to summertime lows.2 At first, many scientists attributed this to the cold weather. However, this isn't entirely accurate since it has been found that the "cold season" also occurrs in warmer regions with rainy seasons.Researchers at the Center for Infectious Disease Dynamics have presented strong evidence showing that different types of weather conditions, beyond just being hot or cold, serve as germ incubators, enabling viruses to spread and migrate as the different seasons change. In fact, they found that in places where the weather stays relatively constant, influenza activity stays constant year-round.3
Based on their findings, they proposed that the tropics might somehow serve as an "influenza reservoir in between influenza seasons." Or put another way, it seems we keep passing colds back and forth across the hemispheres like the great, big, global family that we are.
If cold and flu germs are able to survive in tropical and more weather-consistent areas, how does that relate to our annual cold and flu season? According to a 2006 Harvard study4, the missing link could be airplanes.
Germs and Airplanes
You might find it hard to believe, but the Harvard study found that domestic airline travel volume in November, especially around the Thanksgiving holiday, was an accurate indicator of how rapidly a flu virus will spread. Their research was further supported by the delayed 2001 to 2002 flu season in correspondence to the decline in air travel after the September 11 terrorist attacks.Basically, they found that airplanes allow people and germs to move across the country at a rapid pace. The combination of drier air and people spending more time indoors enables the germs to survive during these times of the year, causing an actual germ migration. So if you live near a travel hub such as Atlanta or New York City, be sure to take extra preventative measures, especially around the popular travel holidays.
What You Can Do
There's no getting around it; germs will spread and the cold and flu season will come and go. But now that you know how it spreads, you can start to prepare your family and take the right measures to keep the germs out of your home all year long.1 Schachter, N. The Good Doctor's Guide to Colds and Flu. 2. 31 Oct 2006.
2 Ibid, p. 69
3 Global patterns in seasonal activity of influenza A/H3N2, A/H1N1, and B from 1997 to 2005: viral coexistence and latitudinal gradients. PLoS One. 2:12. 2007.
4 Brownstein, J.S., et al. Empirical evidence for the effect of airline travel on inter-regional influenza spread in the United States. PLoS Med. 3:e401. Oct 2006.
