Background: To limit the number of susceptible individuals at increased risk for moderate/severe varicella due to a false positive history, proof of healthcare provider diagnosis or verification is recommended as evidence of immunity for those born ≥1980 who report varicella history.
Objectives: To examine the accuracy of medical record (MR) documented varicella history as a measure of varicella-zoster virus (VZV) immunity among unvaccinated individuals born ≥1980.
Methods: As part of a larger cross-sectional study conducted at 3 Philadelphia clinics from 2004-2006, we recruited 536 unvaccinated patients aged 5-19 years. Varicella history was obtained from 3 potential sources: parent/patient interview, any MR documentation including screening during well visits, and MR documentation of an acute visit for varicella. All participants were tested for VZV IgG. For each source and 3 age groups, positive predictive value (PPV) was calculated (percentage with positive VZV IgG results among those with a positive history). Specificity of varicella history, which impacts the number of false positives, was compared between different sources using McNemar’s chi square.
Results: MR documentation of varicella history increased with age from 58% among 5-9 year olds to 85% among 15-19 year olds. The proportion with varicella diagnosed at an acute visit was much lower (6%-13%). Among participants aged 5-9 years, PPV for parent report, any MR documentation, and acute diagnosis documentation were 90% (CI:73%-98%), 96% (CI:82%-100%), and 100% (CI:54%-100%), respectively. Among participants aged 10-14 years, PPV for documentation of an acute visit for varicella was 97% (CI:82%-100%) and its specificity was significantly higher (p<0.0001) than any other source. For older participants (15-19 years), PPV was high (99%-100%) regardless of source.
Conclusions: MR documentation of an acute visit for varicella was a highly accurate predictor of VZV immunity and is a practical way to confirm varicella history for unvaccinated children born between 1985-2001 (participants 5-19 years).