title: A cluster of primary varicella cases among healthcare workers with false-positive varicella zoster virus titers.
abstract: BACKGROUND
  Five cases of primary varicella zoster virus (VZV) we re diagnosed among hospital healthcare workers (HCWs). All had complied with a pre-employment VZV screening program and had been considered immune.
  
  
  OBJECTIVE
  To summarize the investigation of VZV among un-immunized HCWs and to provide recommendations for avoiding false-positive serologic tests.
  
  
  METHODS
  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.
  
  
  METHODS
  Large inner-city, tertiary-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.
  
  
  CONCLUSIONS
  LA may be prone to false-positive results and inappropriate for screening hospital HCWs.
authors.affiliation: Hospital of the University of Pennsylvania, Division of Occupational Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Amy
authors.initials: A
authors.lastname: Behrman
authors.forename: D Scott
authors.initials: DS
authors.lastname: Schmid
authors.forename: Anne
authors.initials: A
authors.lastname: Crivaro
authors.forename: Barbara
authors.initials: B
authors.lastname: Watson
mesh_terms: D000328:Adult; D002644:Chickenpox / Q000175:diagnosis / Q000209:etiology* / Q000635:transmission; D004196:Disease Outbreaks; D004797:Enzyme-Linked Immunosorbent Assay; D005189:False Positive Reactions; D005260:Female; D014645:Herpesvirus 3, Human / Q000276:immunology / Q000472:pathogenicity*; D006786:Hospitals, Urban; D006801:Humans; D007074:Immunoglobulin G / Q000032:analysis; D017757:Infectious Disease Transmission, Professional-to-Patient; D008297:Male; D008875:Middle Aged; D010564:Personnel, Hospital; D011247:Pregnancy; D018570:Risk Assessment; D012698:Serologic Tests
chemical_list: D007074:Immunoglobulin G