Fifth disease - so called because it was historically classified as the fifth classical childhood rash* - is a common pediatric viral infection that causes a mild illness. It is also known as parvovirus B19, slapped cheek syndrome or erythema infectiosum. More than 50% of children aged 15 have antibodies to parvovirus, through previous infection.
The incubation period is four to fourteen days. The prodrome (early symptoms) includes fever, runny nose, sore throat, headache and gastrointestinal upset, and may last for two weeks. Most children, however, appear well.
The rash that follows has two stages. Stage 1 involves the slapped cheek phenomenon, with circumoral pallor (white area around the mouth). Stage 2, which follows one to four days after the facial symptoms, consists of an itchy rash in a lacy pattern of raised, red areas over the trunk and extremities. The rash persists for one to six weeks, and may be exacerbated by sunlight, heat and exercise.
Fifth disease, which is primarily transmitted by respiratory droplets, is highly infectious. 50% of household contacts of an affected person will become infected; 20-30% of teachers exposed to an infected student will catch the virus. The infectious period precedes the onset of the rash. So Ariana, frightful though her appearance may be, does not pose a risk to other children. Children who have been diagnosed with fifth disease may attend daycare or school.
5-10% of children (usually adolescents) and 60-70% of adults develop short-term mild arthritis one to three weeks after the initial infection. In children, the knee is most commonly affected, and in adults, the hands. The joint pain typically improves spontaneously after two weeks.
The diagnosis of fifth disease is a clinical one; blood tests are not typically performed. Treatment is symptomatic only. There is no vaccine.
The transmission rate to the fetus in pregnant women who contract fifth disease is 30%. The risk of miscarriage is 2-6%. Parvovirus can also cause fetal hydrops and congenital infection syndrome. The risk is greatest in the second trimester, and least in the first. Pregnant women who have been exposed to parvovirus should see their physician for blood tests to confirm infection, and serial ultrasound follow-up of the fetus if necessary.
Do not diagnose yourself or your child from the Internet, not even based on physician blogs, thorough and accurate though they may be. There are other conditions that resemble fifth disease, such as rubella, measles, enterovirus and drug rashes. And although fifth disease is usually benign, it can lead to serious complications in some patients, particularly in those who are immunocompromised. An experienced clinician should make the diagnosis.
For more information, check out the Canadian Pediatric Society or Merck. For the unique perspective a physician-mother has on diagnosing her own child with fifth disease, see my related post at Mothers in Medicine.
* The other pediatric exanthems are: measles (first), scarlet fever (second), rubella (third), Duke's disease (fourth) and roseola (sixth).