While it's tempting to blame your last sick day on influenza, chances are you're wrong.

A new study from Imperial College London suggests that the virus is a lot less common in adults than previously thought; adults above the age of 30 only catch the flu about twice every 10 years. It's likely that the illness you thought to be the flu was actually just a strain of the common cold, like rhinovirus or coronavirus. On the flip side, youngsters get the flu much more frequently; the study found they get sick every other year.

"For adults, we found that influenza infection is actually much less common than some people think. In childhood and adolescence, it's much more common, possibly because we mix more with other people," Dr. Steven Riley, senior author of the study, said. "The exact frequency of infection will vary depending on background levels of flu and vaccination."

To get this information, researchers from the United Kingdom, United States, and China collected blood samples from test subjects in China and compared them with a variety of strains of influenza. By looking at the different blood samples, they were able to get a gist of how often the virus entered the patients' bodies.

The researchers used the data to create a mathematical model of how bodies react to disease differently over time. The model supported the findings of other studies that believed that immune systems react stronger to strains of influenza virus encountered earlier in life than those met later.

Researchers hope that these findings will lead to a better understanding of how viruses evolve based on the immune systems of the general public. Ideally, more effective immunizations can be created to help protect against illness.

[h/t: ScienceDaily.com]