Your mother may have told you to wash your hands after handling money. Here's evidence for why: A study published by Swiss researchers shows that an infectious virus can survive for three days on bank notes, and 17 days "in the presence of respiratory mucus" (yuck).

The paper concludes that we can't totally ignore the role that passing bills from one person to another has in the spread of a virus. Indeed, the New York Times reported this week that one researcher is using data from Where's George?, a Website that tracks the path of dollar bills, to help project the current spread of swine flu.

All this passing of dirty money sounds like a great argument for using debit cards, which you keep in your wallet, swipe through a card-reader, and don't pass to anyone else. But they're far from perfect. After all, the buttons you push to authorize the transaction may have been touched by others who were infected.

And as our recent Money post shows, debit cards have other flaws. Among other things, you're likely to spend more with debit cards than when you use cash. You might not get the flu, but you might feel sick upon viewing your bank statement.

So, Mother was probably right. It wouldn't hurt to wash your hands after handling money, and to follow other precautions. And don't assume using a debit card will protect you from anything.--Tobie Stanger