This suggests that children with unexplained fever and low CRP may have had fever due to (1) respiratory viral infections without focal signs, as respiratory viruses have been reported to be frequent in children with non-focal febrile neutropenic patients, (2) other non-focal infections, such as enterovirus, and/or (3) self-limiting reactivation of systemic viruses such as cytomegalovirus (CMV) and Epstein-Barr virus (EBV), although such reactivation has recently been reported to be rare in children with febrile neutropenia [49,50,51,52,53,54]. Here, CRP is linked to viral infectious disease.