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A Cluster of Primary Varicella Cases Among Healthcare Workers With False-Positive Varicella Zoster Virus Titers

Published online by Cambridge University Press:  02 January 2015

Amy Behrman*
Affiliation:
Hospital of the University of Pennsylvania, Division of Occupational Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
D. Scott Schmid
Affiliation:
Centers for Disease Control and Prevention, National VZV Laboratory, Viral Immunology Section, Viral Exanthems and Herpesvirus Branch, Division of Viral and Rickettsial Diseases, National Center for Infectious Diseases, Atlanta, Georgia
Anne Crivaro
Affiliation:
Hospital of the University of Pennsylvania, Immunology Laboratory, University of Pennsylvania, Philadelphia, Pennsylvania
Barbara Watson*
Affiliation:
City of Philadelphia Department of Public Health, Division of Disease Control, Philadelphia, Pennsylvania
*
Occupational Medicine, Hospital of the University of Pennsylvania, 3400 Spruce Street, Philadelphia, PA 19104
Occupational Medicine, Hospital of the University of Pennsylvania, 3400 Spruce Street, Philadelphia, PA 19104

Abstract

Background:

Five cases of primary varicella zoster virus (VZV) were diagnosed among hospital healthcare workers (HCWs). All had complied with a pre-employment VZV screening program and had been considered immune.

Objectives:

To summarize the investigation of VZV among un-immunized HCWs and to provide recommendations for avoiding false-positive serologic tests.

Design:

Risk of transmission of VZV to susceptible HCWs is minimized through serologic screening. Varicella vaccine is recommended for susceptible HCWs. A commercially available latex bead agglutination assay (LA) is widely used because it is rapid and easy to perform. LA was compared with the whole-cell varicella ELISA standardized in the Centers for Disease Control and Prevention (CDC) National Herpes Laboratory.

Setting/Population:

Large inner-city, tertiarycare hospital with a diverse employee population.

Results:

In a year, 5 HCWs presented with laboratory-confirmed primary varicella infection. Four had VZV exposures 2 weeks prior to presentation. All had documented positive VZV titers by LA performed at hire. None were offered VZV vaccination. The original LAs were judged false-positives.

Intervention/Follow-Up Investigation:

Fifty-three consecutive VZV LA samples from the hospital laboratory were retested at the CDC. Forty-four samples concurred. Of the remaining 9, 4 were positive by hospital LA but negative by CDC IgG ELISA. Four were equivocal by hospital LA but negative by CDC IgG ELISA and LA. One was positive by hospital LA but negative by LA and equivocal by ELISA at the CDC.

Conclusion:

LA may be prone to false-positive results and inappropriate for screening hospital HCWs.

Type
Orginal Articles
Copyright
Copyright © The Society for Healthcare Epidemiology of America 2003

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