OBJECTIVE: To elucidate clinical features of patients with primary human herpesvirus 7 (HHV-7) infection and serologic and virologic findings between HHV-7 and human herpesvirus 6 (HHV-6). MATERIALS AND METHODS: During a 19-month observation period, 71 infants and children (35 boys and 36 girls with a mean age of 14.5 months [range, 1 month to 48 months]) who had acute febrile respiratory illness with or without skin rash were examined clinically and virologically. Heparinized blood samples were used for isolation of HHV-6 and HHV-7 and detection of both virus DNA sequences by a nested polymerase chain reaction amplification. Both virus antibody activities were measured by an indirect immunofluorescent assay. RESULTS: HHV-7 infection was observed in 15 (6 boys and 9 girls with a mean age of 12.9 months [range, 7 months to 27 months]), 1 of 10 with upper respiratory infection and 14 (28%) of 50 with febrile exanthem, whereas HHV-6 infection was in 22 (44%) of the 50. Fever (37.5 degrees C) was observed in all 15, with an average maximum body temperature of 38.7 degrees C (range, 37.6 degrees C to 39.8 degrees C), which persisted for 2.9 days (range, 1 to 5 days). Papular, macular, or maculopapular rash was observed in 14 (93%) of the 15, which appeared on day 2.9 of fever (range, days 2 to 5) on the face, trunk, and extremities and persisted for 2.7 days (range, 1 to 5 days). A convulsive seizure that persisted for a few minutes developed in 1 patient on the first day of elevation of fever. HHV-6 antibody was demonstrated in 13 (87%), and a simultaneous significant increase to HHV-6 antibody titers was observed in 8 (53%) of the 15 during primary HHV-7 infection. HHV-7 and HHV-6 DNAs were almost always detected in mononuclear cells (MNCs) during acute and convalescent phases, whereas HHV-7 DNA was positive in some plasma samples obtained during the acute phase of the disease. CONCLUSIONS: Primary HHV-7 infection occurred somewhat later than HHV-6, which was confirmed by the isolation of HHV-7 from blood and/or seroconversion to the virus. Clinical features of a virologically confirmed patient with primary HHV-7 infection were comparable with those of primary HHV-6 infection. Preexisting HHV-6 antibody increased significantly in the half of patients with primary HHV-7 infection. HHV-7 DNA was detected in peripheral blood MNCs and plasma in the acute phase and persisted in MNCs thereafter.
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