Acute varicella-zoster

Centers for Disease Control and Prevention (CDC) 2024 case definition:[74]Centers for Disease Control and Prevention. National notifiable diseases surveillance system (NNDSS): varicella/chickenpox 2024 case definition. Feb 2024 [internet publication]. https://ndc.services.cdc.gov/case-definitions/varicella

Clinical criteria:

• Acute illness featuring:

  • A generalised rash with vesicles (maculopapulovesicular rash) or

  • A generalised rash without vesicles (maculopapular rash), particularly in the absence of a more plausible diagnosis.

Laboratory criteria for confirmation:

• Positive polymerase chain reaction (PCR) testing for varicella-zoster virus (VZV) DNA

• Positive direct fluorescent antibody (DFA) for VZV

• Isolation of VZV in culture

• A significant rise (at least a fourfold increase or seroconversion) in serum VZV-specific immunoglobulin G (IgG) between acute and convalescent phases

Supportive laboratory evidence:

• Detection of VZV-specific immunoglobulin M (IgM) antibody in serum

Epidemiological linkage for confirmation:

• Exposure or contact with a confirmed varicella case, or

• Linkage to a varicella outbreak with at least one laboratory-confirmed case

• Contact with a person displaying herpes zoster symptoms, irrespective of lab confirmation

Criteria to distinguish new cases:

• New onset of symptoms that fulfil the criteria for a confirmed or probable case,

• A previously confirmed case showing a documented period of recovery followed by the reappearance of symptoms that meet case criteria,

• A prior report (not previously confirmed) supplemented by new information that supports a confirmed case

Case classification:

• Probable case: meets clinical criteria with generalised rash with vesicles; or meets clinical criteria with generalised rash and supportive epidemiological evidence or laboratory findings

• Confirmed case: meets both clinical criteria and confirmatory laboratory evidence or epidemiological linkage