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.

Public health experts say policies like these encourage many people with H1N1, commonly called swine flu, to report to work despite official warnings from the government and most companies that they should stay home.

“For people who are really caught on a weekly income, if they can’t make a go of it, they might say, ‘I’m desperate. I’m going to do what I have to do, and I’m going into work even though I’m sick,’” said Robert Blendon, a professor of health policy at Harvard.