Varicella Immunity and History of Infection Maryellen E. Gusic MD Assistant Professor of Pediatrics Penn State Children’s Hospital

Introduction zImmunization against varicella is recommended for susceptible, immunocompetant children over the age of 12 months. zA reliable history of naturally occurring infection is considered to be evidence of immunity.

Introduction continued zInfection rarely occurs without the development of characteristic skin lesions. zParents are usually able to report a history of varicella infection in their child.

Introduction continued zVaricella immunity requires ydevelopment of specific antibodies ystimulation of cell mediated immunity zImmune status of a child can be determined by measuring specific IgG immunoglobulin levels.

Introduction continued zVaricella in infants yA modified specific antibody and cell mediated immune response has been described. xmild infection xeffect of transplacentally acquired antibodies

Introduction continued zNatural infection is thought to provide life long immunity. zReinfections are observed in healthy children. yinaccurate diagnoses? ymodified antibody and/or cell mediated immune response?

Our Study zHypotheses yChildren infected with varicella early in life may have a modified immune response to infection and remain susceptible to reinfection. yChildren whose infection was clinically mild, may not have developed protective antibody titers and thus also remain susceptible to reinfection.

Objectives zTo identify children with a history of natural infection whose illness occurred before 1 year of age zTo identify children whose infection would be classified as mild or moderate by determining the number of skin lesions present during the illness

Objectives continued zTo determine if children with a history of natural infection before 1 year of age or with mild or moderate infection have protective antibody titers zTo determine if further questions to describe the skin lesions present aid in supporting the “reliability” of the history of infection

Methods zChildren with a history of varicella infection identified by chart review and by parental questioning at clinic visits were included. zChildren with a known immunodeficiency were excluded. zA varicella questionnaire was completed.

Methods continued zVaricella questionnaire ypatient’s current age yage at which varicella infection occurred yinfection diagnosed by parent or health care professional ydescription of illness xvesicular, itchy, number of lesions

Methods continued zFinger stick blood samples were obtained for those children whose infection occurred before one year of age or who had less than 250 lesions during their infection. zSerologic testing for anti-VZV IgG antibodies was performed by the National VZV Lab at the CDC.

Methods continued zSerologic testing yELISA assay for anti-VZV IgG antibodies yResults recorded as mean adjusted OD reading and by objective rating x0.166 and above positive yEquivocal results retested at lower serum dilution

Methods continued zOdds ratios were determined and a Chi square analysis was performed on the data. zResearch was approved by the Institutional Review Board of the Hershey Medical Center and the Penn State University College of Medicine.

Results z32 patients were enrolled in the study y11 children had <50 lesions y21 children had moderate infection y17 children were infected before 1 year of age x5 children whose infection occurred before 1 year of age had mild infection xNo child whose infection occurred before 1 year of age had >250 lesions

Results continued z30 patients underwent serologic testing y4 patients had negative antibody titers y6 patients had equivocal serologic results

Conclusions zChildren with a history of mild varicella infection should be evaluated to determine if they have protective antibody titers. zAn immunocompetant child aged 12 months or older who has negative antibody titers should be immunized against varicella zoster virus.

Conclusions continued zDetermining if the rash associated with the infection was itchy may further support the reliability of the diagnosis. zBoth parents and health care professionals may incorrectly identify an illness as varicella.

Limitations of this Study zPower of study limited by the small number of patients enrolled zResults dependent upon parental reporting of age of infection, symptoms of disease zNegative serologic titers may be result of inaccurate diagnoses

Implications for Future Research zStudies are needed to determine the factors that may interfere with the development of life long protective immunity to varicella infection. zFurther studies identifying the clinical signs and symptoms that ensure the accuracy of diagnosing varicella have important public health considerations.

A Special Thanks to... z Dr. Scott Schmid and the National VZV lab at the CDC zBeth Anne Nagy, MS II, Penn State College of Medicine zDavid Mauger, PhD, Department of Health Evaluation Sciences, Penn State College of Medicine