Erythema infectiosum was recognized in 1889 as a common exanthem of childhood. It was originally called fifth disease because it was classified as the fifth in a series of childhood exanthems (Table). Fifth disease was a childhood illness characterized by mild fever, erythematous cheeks, and a lacelike rash on the trunk and proximal extremities. The illness usually occurred during winter and spring in localized epidemics and there were no known sequelae.1,2
In 1975, during routine screening of serum samples for hepatitis B virus surface antigen, false-positive results were obtained from nine units of blood. These tests were positive by counter immunoelectrophoresis, but were negative by the more specific passive hemagglutination test. Examination of these specimens by electron microscopy did not reveal the 27-nm viral particles of hepatitis B virus surface antigen, but instead, smaller 23-nm viral particles were revealed. These 23-nm viral particles were designated B-19, the specimen label
Feder HM, Anderson I. Fifth Disease: A Brief Review of Infections in Childhood, in Adulthood, and in Pregnancy. Arch Intern Med. 1989;149(10):2176–2178. doi:10.1001/archinte.1989.00390100014005
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