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(also fifth disease), an infectious disease primarily of children between the ages of five and 12, characterized by an erythematous rash. The causative agent, which is unknown, presumably enters the body in droplets suspended in the air. The incubation period is one to two weeks. Red, raised, confluent spots appear on the cheeks. Eruptions then appear on the trunk and extensor surfaces of the limbs, where they coalesce to form indistinct erythema patches. They gradually disappear, leaving behind marmoreal markings after six to ten days. The patient’s general condition usually remains good.