Fifth disease, or erythema infectiousum is a common childhood illness caused by the human parvovirus B19. It is also called 'slapped cheeks' disease, because of the distinctive rash that accompanies this illness. Symptoms are usually mild, and if present, can include a runny nose, sore throat, headache and a low grade fever. About 7-10 days later, your child may develop a very red rash on both of his cheeks, with a pale area around his mouth, giving the appearance that his cheeks have been slapped. These red patches may be warm to the touch, but will be nontender.

Next, a red or pink lacelike rash develops on his arms and legs, as the rash on his cheeks begins to fade. This lacy rash is usually flat, but may be slightly raised, may be mildly itchy, will come and go for a couple of weeks (up to 5 weeks in some cases) and may become worse when your child becomes overheated (after a bath, etc.) or exposed to the sun. The rash may also spread to his buttocks and/or trunk.

Children can also become infected with parvovirus B19 and not have any symptoms.

Fifth disease is a very common illness, and up to half of teenagers, if tested, will show evidence of having this infection in the past.

About half of the household members that are exposed to someone who develops fifth disease will also become infected, although it can take between 4 and 14 (and up to 21) days for the initial symptoms to begin, and then another 2-3 weeks for the rash to appear. It is less likely for school contacts to become infected, and only about 20% of susceptible children will develop fifth disease after being exposed.

Children with fifth disease are only contagious before the rash appears, so they do not need to be excluded from school or day care once they develop the rash. While this illness is very mild in most children and no treatment is required, if your child has a blood disorder, immune system problems or if you are pregnant, it can rarely cause more serious problems, including aplastic anemia, and you should consult your doctor for advice.

While blood tests are available to confirm an infection or to show that a person had the infection in the past, they are usually reserved for children with chronic medical problems, such as blood and immune system disorders, or pregnant women who are exposed to fifth disease early in their pregnancy.

Adults who get fifth disease can develop a similar illness which can be complicated by arthritis.