Thinking Numerically

I have heard that there are something like 450 common cold viruses -- those viruses which cause the symptoms of the common cold. This explains why you can keep catching colds even after your body has made antibodies to fight off the infection caused by a previous virus. And, it explains why you keep getting colds, year after year. After all, you'd think that eventually you'd become immune to them. But, think about this. If you live to the average life span of 75, then, in order to contract each cold virus, you'd have to have 450/75 or 6 colds per year, for every year of your life. Since I only get about 2 or 3 a year, now, I'm destined to keep getting colds!

As an aside, I was unable to verify this statistic online. Also, I don't know (but suspect) that some of the viruses are constrained by geography, much like other diseases are. So, you may experience a decrease in the number of viruses you contract per year because only a fraction of them exist in your locale, and therefore, you may contract many of them before the end of your life.