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Varicella / Chickenpox
1999 Case Definition

Clinical Description

An illness with acute onset of diffuse (generalized) maculo-papulovesicular rash without other apparent cause.

Laboratory Criteria for Diagnosis

  • Isolation of varicella virus from a clinical specimen, OR
  • Direct fluorescent antibody (DFA), OR
  • Polymerase chain reaction (PCR), OR
  • Significant rise in serum varicella immunoglobulin G (IgG) antibody level by any standard serologic assay

Case Classification


A case that meets the clinical case definition, is not laboratory confirmed, and is not epidemiologically linked to another probable or confirmed case


A case that is laboratory confirmed or that meets the clinical case definition and is epidemiologically linked to a confirmed or probable case


Two probable cases that are epidemiologically linked would be considered confirmed, even in the absence of laboratory confirmation.

In vaccinated persons who develop varicella more than 42 days after vaccination (breakthrough disease), the disease is almost always mild with fewer than 50 skin lesions and shorter duration of illness. The rash may also be atypical in appearance (maculopapular with few or no vesicles).

Laboratory confirmation of cases of varicella is not routinely recommended; laboratory confirmation is recommended for fatal cases and in other special circumstances.