But what if you're one of the estimated 57 million working Americans with no paid sick days? Staying home could mean losing a paycheck, or worse, losing your job entirely.
The prospect of workers showing up with swine flu -- or sick kids infecting their schoolmates -- is bringing added urgency to efforts to pass a federal law guaranteeing paid sick leave.
"The problem has really come into sharp relief the past few days," said Debra Ness, the president of the National Partnership for Women and Families. "Many people don't even realize that almost half the private sector -- 48 percent -- has no sick days, not even a single one."
Those least likely to have sick leave are low-income workers, particularly in fields such as food services, child care and the hotel industry.
The Associated Press interviewed a number of workers in the food industry. Most didn't want their names used for fear they would be fired. They told stories of coming to work sick to keep their jobs, and of seeing sick co-workers sneezing and coughing near food.
A study on sick leave found that 68 percent of those without paid sick days had gone to work with a contagious illness. And one of six workers reported they or a family member had been fired, suspended or punished after taking time off, according to the 2008 study by the University of Chicago's National Opinion Research Center.
Earlier this week, Sen. Edward M. Kennedy, D-Mass., and Rep. Rosa DeLauro, D-Conn., sought sponsors to reintroduce the Healthy Families Act, which would let workers earn up to seven paid sick days a year.
Kristin Rowe-Finkbeiner, a co-founder of MomsRising, which lobbies on issues concerning working women and families, pointed to a 2004 study by Cornell University showing that "presenteeism" -- people showing up for work sick -- costs the economy $180 billion annually in lost productivity, or more than $250 per employee per year.
That's more, they said, than the cost of providing sick days.