Rash on the face on a 4 y...

A 4-year-old boy is brought to your office by his mother for evaluation of a rash on his face that his mother first noticed the day prior to presentation. His mother comments that it looks like somebody "slapped him:' The mother reports that he has had a cold for the last couple of days. The child's physical examination is unremarkable except for an erythematous macular rash over both cheeks. The mother admits that the child is behind on his immunization schedule.