For 20 million Americans, staying home sick is a luxury. Every year, that many people go to work with a virus or infection because they don't have paid sick leave, even though research shows that staying home prevents the flu from spreading. And during a nasty flu season like this one—we're now likely in for a record-setting year—doctors and public health officials urge Americans to take every precaution they can to avoid spreading the potentially deadly virus.

"For those who are already sick, please stay home from work or school," acting director of the Centers for Disease Control Anne Schuchat urged on a recent call with reporters. "That is such an important recommendation to follow. Otherwise you run the risk of spreading the virus to others—and what may be mild symptoms to you could be deadly to someone else."

But in reality, as scientifically sound as this reasoning may be, taking unpaid days off for whatever reason, is simply not an option for many Americans. The United States is the only wealthy country that doesn't guarantee paid days off for illness. That leaves it up to companies to decide whether to dole out the benefits, which often means that upper-level employees at large companies get paid sick leave, but low-wage workers often don't. And those are exactly the people who can't afford to take days off.