I second Fifth's Disease. It is characterized by cheeks that looked like they have been slapped. It went around the school where I taught one year but the doc said it wasn't a big deal. Here is some info I found...
"Fifth disease is a mild illness usually without a fever caused by parvo virus B19. Severe complications are rare but people with chronic blood disorders may develop an inability to form new blood cells and develop anemia. During pregnancy the virus can infect the unborn child, which can result in death of the fetus.
It is spread by exposure to secretions or droplets from the nose and throat. It occurs more commonly in children of elementary school age.
The symptoms start with a low grade fever and fatigue. A red rash which looks like a slap mark commonly appears on the cheeks and a fine lace-like rash may appear on the body. The rash may be itchy. Some people have mild signs of illness or no symptoms at all. The above symptoms are more common in children. Adults more commonly have arthritic pain and less rash or fever.
Symptoms start 1-2 weeks after exposure.
A person is most contagious about one week before the onset of the rash, and once the rash starts, it probably cannot be spread to others.
There is no specific treatment.
If you have had fifth disease it is thought that people develop long-term immunity. Studies show that about 50% of adults have immunity to fifth disease.
You do not have to be excluded from work or school because the contagious stage happens before most of the symptoms. Pregnant women should avoid exposure to persons infected. Pregnant women with sick children at home should be advised to wash hands frequently and avoid sharing eating utensils."
Hope this helps!
