Complain!! There are very few times I think it is necessary for customers to complain to management or to the Health Department but this is one of them. Those of us behind the counter have no say in this person being present. When someone is forced by management to come to work ill they are condemning the rest of us to sickness as well. Trust me we are not ok with this.
Do your consumerly duty to the rest of us and complain. You bitch and moan when your latte isn't 143 degrees, this is something that actually matters. Bitch about it. Believe it or not consumers have the power in this position, if you see something going on that isn't right tell a manager that you are not ok with sick people serving you coffee. They HAVE to do something about it!