Confirmed primary HHV-6 infection in children with suspected encephalitis.

HHV-6 infection has been associated with neurological symptoms in children. Two variants of human herpes virus 6, HHV-6A and HHV-6B, have been identified. Their role in neurological infections is poorly understood. We studied 53 children with suspected encephalitis for HHV-6A (strain GS) and HHV-6B (strain Z29) antibodies using an indirect immunofluorescence test. Primary infection was separated from past infection by an IgG-avidity test. The identified primary infections were studied for HHV-6 specific DNA by PCR. Forty-one children of 53 had IgG antibodies to HHV-6. Six children had low avidity of HHV-6 IgG antibodies indicating acute primary infection; four to type A, one to B, and one to both types. By serology, HHV-6 viral etiology was suggested in 6/53 (11.3%) of cases. One of the six patients with primary infection had HHV-6 DNA in serum and two in CSF. The children with primary HHV-6 infection were significantly younger than the whole series, 2.3 years vs. 6.4 years. We conclude that primary HHV-6 infection appears to be an important associated or causative agent in neurological infections of young children, and it can be confirmed from a single serum specimen using the IgG-avidity test.