VARICELLA SEROLOGY AMONG SCHOOL-AGE-CHILDREN WITH A NEGATIVE OR UNCERTAIN HISTORY OF CHICKENPOX

Background. Clinicians who offer varicella vaccination to school age c hildren face the dilemma of whether to serotest or vaccinate presumpti vely. Varicella seroprevalence among 7- to BE-year-old children with n egative or uncertain histories has not. previously been studied, Our m ain objective was to describe varicella seroprevalence among children ages 7 to 12 years with a negative or uncertain history of chickenpox, Methods. This was a cross-sectional study of children whose clinician s had ordered varicella serotesting. Guidelines from the medical group 's regional pediatric infectious disease specialists recommended obtai ning varicella serology on all children 7 to 12 years old with a negat ive or uncertain history. Parents were interviewed by telephone about the child's history of chickenpox before test results were completed, Results. Varicella seroprevalence ranged from 9% amomg 7-year-olds who se parents said they had definitely not had chickenpox to 68% among 11 -year-olds whose parents were not sure whether they had had chickenpox . Among children whose parents were uncertain about their chickenpox h istory, almost one-half (48%) were seropositive. Twenty-five percent o f children whose parents said they definitely had not and 32% of child ren whose parents said they had probably not had chickenpox were serop ositive. Of parents whose children had experienced serotesting, 73% sa id they would prefer to have the blood test first rather than presumpt ive vaccination. For a large health maintenance organization, it was p rojected to be most cost-effective (in terms of cost per chickenpox ea se prevented) to recommend testing for children 9 to 12 years old with uncertain histories of chickenpox. Conclusions. We conclude that amon g children 7 to 12 years old with negative or uncertain histories of c hickenpox, a varicella seroprevalence ranges from 9 to 68% depending o n age and clinical history. Parents are generally receptive to serotes ting, although individual preferences vary. In the population we studi ed it would be most cost-effective to recommend testing before decidin g about vaccination for children 9 to 12 years old with uncertain hist ories of chickenpox.