Susceptibility to varicella zoster of children with cystic fibrosis

Varicella zoster virus (VZV) infection can result in significant morbidity in patients with cystic fibrosis (CF), and the risk of severe pulmonary complications rises with age [1]. This is a greater concern in those receiving systemic corticosteroids, which in the case of CF is most often given for acute allergic bronchopulmonary aspergillosis (ABPA). Severe complications such as pneumonitis, secondary bacterial infections, and liver failure may occur despite prompt treatment with antiviral agents. The seroprevalence of VZV antibodies in CF children is unknown, although in the general population N80% of children over 6 years of age have evidence of immunity [2]. We aimed to investigate the seroprevalence of VZV antibodies in children attending our large paediatric specialist CF centre, whether or not there was a history of chicken pox. In 2011 we started routine testing for VZV antibodies in 6 year olds at their annual review. This age was selected in view ofthelowprevalenceofABPAunderthatageandthechancethat children would already have had chicken pox. Evidence of immunity to VZV was determined by VZV IgG antibodies ≥0.9 IU/L (measured by a VIDAS VZV IgG enzyme-linked fluorescent immunoassay). In 2012 the prevalence of ABPA in our CF clinic was 9%, 96% of which was aged 6 and above. As this was a new policy, we also tested older children in order to cover the whole clinic. We identified all children in our CF clinic aged ≥6 years at August 2012, and collected data on