Classifying Varicella Cases Flowchart

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How to Classify Confirmed & Probable Varicella Cases During Investigations

Does the case meet the clinical definition of varicella in the absence of a more likely alternative diagnosis? This means the case has a generalized maculopapulovesicular rash or maculopapular rash.

A) If yes and there is a rash with vesicles

1. First ask if the varicella case has been lab-confirmed by PCR, DFA, VZV isolation, or diagnostic serology.
   1. Diagnostic serology includes a significant rise (i.e., at least a 4-fold rise or seroconversion) in paired acute and convalescent serum VZV IgG antibody.
2. If the case has been lab-confirmed, then classify as confirmed case.
3. If the case is NOT lab-confirmed, then ask if case had a confirmatory epi linkage to a: lab-confirmed case, OR varicella cluster/outbreak with at least 1 lab-confirmed case, OR person with herpes zoster (regardless of lab confirmation).
4. If case had a confirmatory epi linkage, then classify as confirmed case.
5. If case had NO confirmatory epi linkage, then classify as probable case.

B) If yes and there is a rash without vesicles

1. First ask if the varicella case has been lab-confirmed by PCR, DFA, VZV isolation, or diagnostic serology.
   1. Diagnostic serology includes a significant rise (i.e., at least a 4-fold rise or seroconversion) in paired acute and convalescent serum VZV IgG antibody.
2. If the case has been lab-confirmed, then classify as confirmed case.
3. If the case is NOT lab-confirmed, then classify as probable case, only if it meets 1 of the following criteria:
   1. Has confirmatory epi linkage to a: lab-confirmed case, OR varicella cluster/outbreak with at least 1 lab-confirmed case, OR person with herpes zoster (regardless of lab confirmation).
   2. Has presumptive epi linkage to a: probable case with generalized rash with vesicles.
   3. Has a positive VZV IgM.

C) If clinical definition of varicella is unknown

If you have a case with a provider diagnosis but with no rash details, this means the case meets the healthcare record criteria.

1. Follow up with the provider to obtain rash details if you only have a diagnosis.
2. Ask if the varicella case has been lab-confirmed by PCR, DFA, VZV isolation, or diagnostic serology.
3. If the case has been lab-confirmed, then classify as confirmed case.
4. If the case is NOT lab-confirmed, then classify as probable case, only if it meets 1 of the following criteria:
   1. Has confirmatory epi linkage to a: lab-confirmed case, OR varicella cluster/outbreak with at least 1 lab-confirmed case, OR person with herpes zoster (regardless of lab confirmation).
   2. Has presumptive epi linkage to a: probable case with generalized rash with vesicles.
   3. Has a positive VZV IgM.

Read more about the varicella position statement at: https://cdn.ymaws.com/www.cste.org/resource/resmgr/ps/ps_2023/23-ID-09_Varicella.pdf