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Laboratory studies of acute varicella and varicella immune status
H H Balfour1, C K Edelman, C L Dirksen
1Department of Laboratory Medicine and Pathology, University of Minnesota Health Sciences Center, Minneapolis.
Insights
Optimizing varicella-zoster virus (VZV) culture methods significantly improved detection rates and reduced time to positivity. Antibody assays like FAMA and Whittaker ELISA show promise for immune status and acute varicella diagnosis.
Area of Science:
- Virology
- Immunology
- Clinical Diagnostics
Background:
- Varicella-zoster virus (VZV) diagnosis relies on viral culture and serological assays.
- Accurate and timely diagnostic methods are crucial for managing varicella infections and evaluating vaccine efficacy.
Purpose of the Study:
- To evaluate and optimize VZV culture techniques.
- To assess the performance of different serum antibody assays for VZV detection and immune status determination.
Main Methods:
- Specimens from 620 children were used for VZV culture and serum antibody testing.
- Initial VZV culture methods were modified to improve sensitivity and reduce days to positivity.
- Fluorescent antibody to membrane antigen (FAMA) and enzyme-linked immunosorbent assay (ELISA) methods were compared.
Main Results:
- Modified VZV culture increased detection from 51% to 80% and shortened positivity time.
- The Viran FAMA assay was found to be difficult to read and not reproducible.
- Standard FAMA demonstrated higher sensitivity for vaccine-induced antibodies than the Merck ELISA.
- Whittaker ELISA was comparable to FAMA for immune status testing (95% sensitivity, 92% specificity) and acute varicella diagnosis.
Conclusions:
- Optimized VZV culture methods enhance diagnostic yield and speed.
- FAMA and Whittaker ELISA are valuable tools for assessing VZV immunity and diagnosing acute varicella, with specific strengths for each application.
Abstract:
We evaluated varicella-zoster virus (VZV) culture and serum antibody methods utilizing specimens from 620 children enrolled in protocols for prevention or treatment of varicella and samples routinely submitted to the Clinical Virology Laboratory. In a foreskin fibroblast tube culture system, we initially isolated VZV from only 29 (51%) of 57 children cultured on the first day of varicella. After modifying the method, the proportion of culture-positive children increased significantly to 36 (80%) of 45 (p less than 0.005 by corrected X2), and the median days-to-positivity were significantly shortened from 5.6 to 3.8 days (p less than 0.001, Wilcoxon rank-sum test). The Viran fluorescent antibody to membrane antigen (FAMA) assay was difficult to read and not reproducible. The standard FAMA was more sensitive than the Merck ELISA antibody test for detecting vaccine-induced antibody. The Whittaker ELISA did not detect vaccine-induced antibody but was comparable to FAMA for immune status testing (sensitivity, 95%; specificity, 92%) and for diagnosis of acute varicella.