Conveying the message "stay at home if you're sick" should start at the manager and supervisor levels. Employees are probably more apprehensive about staying out because of their bosses' reaction, rather than because of any company policy. Have supervisors briefly review your company policies on sick days, etc. for workers and state that absences resulting from legitimate illnesses cannot be held against employees at performance evaluations, etc. Reinforce the message in company communications (intranet, newsletters, etc.)
I think that IrisD was on the right track, but managers and supervisors must set an example by staying at home when THEY are sick!
We are a manufacturer, so our plant workers can't telecommute or work at home.
However, we have a crosstraining program so two or three workers (in addition to the "swing" people we always have available) can fill in at running machines and doing processes. Now our workers aren't worried about missing montly production goals, someone they don't know messing up their work area, etc. and are more willing to stay out when they are sick.