When I picked the boys up from daycare the other day, I was informed that Kieran could not return until he had been cleared by his doctor. The staff feared he had…fifth disease.

So, I quickly ran home and looked it up at emedicine.com. The results were chilling.

Background: Erythema infectiosum is a common childhood exanthem caused by human parvovirus B19 (PV-B19), in which a classic 3-phased cutaneous eruption follows a rarely noticed prodrome.

Pathophysiology: The development of erythema infectiosum in children is a normal response to infection by PV-B19. Acute infection in a host who is immunocompetent leads to a Th-1–mediated cellular immune response, with the production of specific immunoglobulin M (IgM) antibodies and subsequent formation of immune complexes.

Oh no, I thought, our little boy has parvovirus B19 and he’s going to have a cutaneous eruption. Why, God, why?

It turns out that fifth disease, or “slapped-cheek disease”, is actually kind of wussy (unless you’re a fetus, in which case it’s really serious). In the early stages, the symptoms are identical to the common cold. It’s not until the child’s cheeks turn bright red that you can recognize the infection, and by that point it’s too late – the infection has run its course.

So why is it called fifth disease? Good question, loyal reader. It turns out there are six traditional childhood rashes, including measles (first disease), scarlett fever (second disease), rubella (third disease), Duke’s disease (fourth disease), and roseola (sixth disease).

So now you know, and knowing is half the battle.