Background Chickenpox and shingles, caused by varicella Zoster virus (VZV), are normally mild self-limiting illnesses in children. Few data exist on the incidence of complicated VZV infection in Ireland. Such data are necessary to inform national immunisation policy.

Objectives To determine the incidence and estimate the minimum disease burden of complicated VZV infection in Irish children.

Methods For this study complicated VZV infection is defined as: any child admitted to hospital because of VZV infection or an associated complication. From January to December 2007 data on hospitalised cases of VZV were prospectively collected from Irish paediatricians reporting to the Irish Paediatric Surveillance Unit. Additional cases were collected from the hospital inpatient enquiry system. The incidence was calculated using age-specific denominators from the 2006 population statistics.

Results To date, details have been returned on 124 children hospitalised with VZV infection. Full details are available for 107 children. The calculated minimum annual incidence of complicated VZV infection in Irish children (<15 years of age) is 10.18/100 000. 87% (93/107) of the children were previously healthy. The median age was 3 years. Sixty-three (59%) were male. Complications included: skin and soft tissue infection in 39 children (36%); neurological complications in 16 (15%); periorbital cellulitis in 7; pneumonia in 6 (2 empyema,); septicaemia in 3; bone and joint infections in 2 and one had metabolic decompensation.

Conclusions VZV infection is associated with significant morbidity. The majority of affected children were previously healthy. Such illness may be preventable by universal immunisation.