A 7-year-old girl with sickle cell anemia was brought to her physician by her parents who reported that she seemed to be extremely fatigued and pale-looking. They stated that several of her classmates had recently had rashes and bright red cheeks. On examination, the doctor did not see a rash, but observed that her conjunctiva, gums, and nail beds were pale and that she had tachycardia. A CBC revealed that her hemoglobin level had fallen by 2 g/dL from her last result 3 months ago; her reticulocyte count was 0.05%. From which of the following is this child suffering?

Parvovirus B19 causes erythema infectiosum in previously well children and adults that often results in a drop in hemoglobin level that is not noticed. In children with chronic hemolytic anemias, such as sickle cell disease, parvovirus B19 infection can result in aplastic crisis (a) associated with a drop in the hemoglobin level of 2 g/dL or more. This can necessitate hospitalization in these children. The virus preferentially infects erythroid precursors. The child has tachycardia from the anemia. There is nothing in the history to suggest Coxsackievirus B pericarditis (b), Norovirus gastroenteritis (c), or BK polyomavirus hemorrhagic cystitis (e); nor is there any reason to suspect Coltivirus infection (d), which would be associated with location, season, and tick bite. Norovirus gastroenteritis is not associated with bleeding. Additional complications of parvovirus B19 infection include maternal transplacental infection of the fetus with resultant fetal hydrops related to anemia in the fetus, unremittent anemia in immuno-suppressed persons such as transplant recipients, and polyarthropathy/arthritis in adults.