Public health experts worried about the spread of the H1N1 flu are raising concerns that workers who deal with the public, like waiters and child care employees, are jeopardizing others by reporting to work sick because they do not get paid for days they miss for illness.

Tens of millions of people, or about 40 percent of all private-sector workers, do not receive paid sick days, and as a result many of them cannot afford to stay home when they are ill. Even some companies that provide paid sick days have policies that make it difficult to call in sick, like giving demerits each time someone misses a day.