Erythema infectiosum, caused by human parvovirus B19 (B19V), is difficult to diagnose by its clinical symptoms and is often misdiagnosed as measles or rubella. Timely confirmation of measles/rubella or other viral etiologies via laboratory tests can provide an accurate picture of the infection status, which can appropriate response. The purpose of this study was to determine the contribution of B19V as an etiological agent for fever‐rash in suspected cases of measles and rubella in Osaka Prefecture between 2011 and 2021. Of 1356 suspected cases, 167 were confirmed with measles and 166 with rubella using nucleic acid testing (NAT). Of the remaining 1023 cases, 970 from which blood specimens could be obtained were screened by real‐time polymerase chain reaction for B19V, from which 136 (14%) tested positive. Of the positives cases, 21% were young children (9 years and younger), while 64% were adults (20 years and older). Phylogenetic tree analysis showed that 93 samples belonged to genotype 1a. The importance of B19V in the etiology of fever‐rash illness was revealed in this study. The importance of laboratory diagnosis by NAT in maintaining the status of measles elimination and to eliminate rubella was reaffirmed.

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