The patient has parvovirus B19 infection. She has chronic hemolytic anemia due to sickle cell anemia and presents with severe anemia and a completely inadequate reticulocyte response 1 week after being exposed to a child with a febrile illness, which was likely caused by parvovirus B19. Hydroxyurea could lead to worsening anemia in a patient with sickle cell anemia but would not cause the acute signs or symptoms found in this patient. A subsequent bone marrow examination would demonstrate pure red cell aplasia (PRCA). Parvovirus has a tropism for erythrocyte precursors and is a known cause of aplastic crisis in patients with underlying sickle cell disease (SCD). Immune competent patients and those without chronic hemolysis have a milder hematologic response to parvovirus infection and are more likely to recover spontaneously.

Cytomegalovirus could cause constitutional symptoms and could trigger a painful crisis, but it is not associated with direct destruction of erythrocyte precursors. Cytomegalovirus may cause retinitis, gastroenteritis, or hepatitis in an immunocompromised patient, none of which are seen in this patient. Adults with SCD are functionally asplenic.

Epstein-Barr virus is unlikely owing to its lack of association with PRCA. However, viral illnesses are the frequent underlying causes that precipitate vaso-occlusive crises or acute chest syndrome in patients with SCD.

Influenza A virus is an unlikely diagnosis because the patient has no typical symptoms. Although influenza A could cause severe viral pneumonia and could lead to acute chest syndrome, its association with PRCA is not strong.