Movie where two couples are stuck inside because of an airborne disease?

I remember seeing a trailer for a movie where one couple visits another and the two are stuck together in the house because of an airborne disease outside. Other people come along and knock on the door seeking shelter, but are told they can't come in because they might be carrying the contagion and because they hadn't shown up on time anyway (for whatever get together the couple was hosting).

I had thought that Carnage was the movie, but it turns out not to be.