In a series of seroepidemiologic studies, seroconversion to HHV-7 was observed in children who were already HHV-6-seropositive. Therefore, prior infection with HHV-6 did not protect against subsequent infection with HHV-7. In an analysis of a large number of serum samples, most children older than 2 years were immune to HHV-6 (as expected), but a majority of 2-year-old children had no HHV-7 antibody. These children seroconverted to HHV-7 over the next 3 to 5 years. Currently, HHV-7 diagnostic testing is performed mainly in individual herpesvirus research laboratories.

Usually, the disease caused by HHV-7 infection is not apparent, although HHV-7 seroconversion sometimes leads to a syndrome similar to roseola. HHV-7 frequently can be isolated from the saliva of healthy adults around the world. Transmission of HHV-7 has been documented clearly in multigenerational families living in the same household.

Transmission does not occur at parturition. However, nearly 100% of older children exhibit evidence of prior HHV-7 infection, as demonstrated by virus isolation from saliva. The percentage of children who acquire HHV-7 from their mothers is approximately 50%; those who acquire the disorder from their fathers, approximately 25%; and those who acquire the disease from other individuals, approximately 25% (Fig. 198.1).