Characteristics and acquisition of human herpesvirus (HHV)-7 infections in relation to infection with HHV-6

Although both human herpesvirus (HHV) 6 and HHV-7 infections are ubiquitous during childhood, few acute HHV-7 infections are identified. It is unknown whether HHV-7 viremia indicates primary infection, as with HHV-6, or reactivation, and if these differ clinically. We studied, in otherwise healthy children <= 10 years old, HHV-7 and HHV-6 infections and their interaction by serologic assessment, viral isolation, and polymerase chain reaction. In children <= 24 months of age, HHV-7 infections occurred less often than HHV- 6 infections (P <= .002). Of 2806 samples from 2365 children <= 10 years old, 30 (1%) showed evidence of HHV- 7 viremia; P <= .002 23 ( 77%) of these were primary and 7 (23%) were reactivated HHV-7 infections. Four ( 13%) showed concurrent HHV-6 viremia, 2 associated with primary HHV-7 infections. The clinical manifestations of primary and reactivated HHV-7 infections were similar, except that seizures occurred more frequently in reactivated infections. These findings, previously unrecognized in otherwise healthy children, suggest that HHV- 7 viremia could represent primary or reactivated infection and may be affected by the interaction between HHV- 6 and HHV-7.