Validity of Reported Varicella History as a Marker for Varicella Zoster Virus Immunity Among Unvaccinated Children, Adolescents, and Young Adults in the Post-Vaccine Licensure Era
We assessed the validity of reported varicella history as a marker for varicella zoster virus immunity among unvaccinated persons 1 to 29 years of age, and we examined varicella disease characteristics associated with varicella zoster virus immunity among those reporting positive histories. We conducted a cross-sectional study at 7 community-based sites in Philadelphia, Pennsylvania, between June 2004 and May 2006 and recruited 1476 participants 1 to 29 years of age who had not been vaccinated against varicella. Sensitivity, specificity, and positive predictive value were determined by comparing self-reported or parent-reported varicella histories from a standardized study interview with varicella zoster virus immunoglobulin G serological results for each participant. We performed multivariate logistic regression analyses to determine which disease characteristics best predicted seropositivity. The sensitivity of reported varicella history was highest (81%-89%) among participants > or =10 years of age, whereas specificity was highest among participants 1 to 4 years of age (99%) and > or =20 years (88%). Reported varicella history was highly predictive of seropositivity (>95%) only among participants > or =15 years of age. For participants 10 to 14 years of age, parental reports of a generalized itchy rash with 1 of the following were highly predictive of seropositivity: varicella transmission to another household member or being raised in a household with no other children. Among participants < or =9 years of age, no combination of disease characteristics was both highly predictive of seropositivity and common. The validity of reported varicella history varies according to age, and a reported history is no longer highly predictive of seropositivity among cohorts born since 1994 (participants < or =9 years of age). Universal varicella vaccination, regardless of history, for these children should be considered, as should simplified criteria for varicella zoster virus immunity among unvaccinated persons born before 1994.