Human herpesviruses-6 and-7 each cause significant neurological morbidity in Britain and Ireland

Background: Primary human herpesvirus-6 and - 7 (HHV-6/-7) infections cause febrile illness sometimes complicated by convulsions and rarely encephalopathy. Aims: To explore the extent of such HHV-6 and - 7 induced disease in young children. Methods: In a three year prospective study in Britain and Ireland, 205 children ( 2 - 35 months old) hospitalised with suspected encephalitis and/or severe illness with fever and convulsions were reported via the British Paediatric Surveillance Unit network. Blood samples were tested for primary HHV-6 and - 7 infections. Results: 26/156 (17%) of children aged 2 - 23 months had primary infection ( 11 HHV-6; 13 HHV-7; two with both viruses) coinciding with the acute illness; this was much higher than the about three cases expected by chance. All 26 were pyrexial; 25 had convulsions ( 18 status epilepticus), 11 requiring ventilation. Median hospital stay was 7.5 days. For HHV-6 primary infection the median age was 53 weeks ( range 42 - 94) and the distribution differed from that of uninfected children; for HHV-7, the median was 60 weeks ( range 17 - 102) and the distribution did not differ for the uninfected. Fewer (5/15) children with primary HHV-7 infection had previously been infected with HHV-6 than expected. Conclusions: Primary HHV-6 and HHV-7 infections accounted for a significant proportion of cases in those,2 years old of severe illness with fever and convulsions requiring hospital admission; each virus contributed equally. Predisposing factors are age for HHV-6 and no previous infection with HHV-6 for HHV-7. Children with such neurological disease should be investigated for primary HHV-6/-7 infections, especially in rare cases coinciding by chance with immunisation to exclude misdiagnosis as vaccine reactions.