Varicella

2023 Case Definition

CSTE Position Statement Number: 23-ID-09

Case Classification

A1. Clinical Criteria

In the absence of a more likely alternative diagnosis:

An acute illness with a generalized rash with vesicles (maculopapulovesicular rash), OR
An acute illness with a generalized rash without vesicles (maculopapular rash).

A2. Laboratory Criteria ^*a

Confirmatory Laboratory Evidence:

Positive polymerase chain reaction (PCR) for varicella-zoster virus (VZV) DNA,^b,cOR
Positive direct fluorescent antibody (DFA) for VZV DNA, OR
Isolation of VZV, OR
Significant rise (i.e., at least a 4-fold rise or seroconversionc,^d) in paired acute and convalescent serum VZV immunoglobulin G (IgG) antibody. ^c,e

Presumptive Laboratory Evidence:

Supportive Laboratory Evidence:

Positive test for serum VZV immunoglobulin M (IgM) antibody.^c,f

^*Note: The categorical labels used here to stratify laboratory evidence are intended to support the standardization of case classifications for public health surveillance. The categorical labels should not be used to interpret the utility or validity of any laboratory test methodology.
^aA negative laboratory result in a person with a generalized rash with vesicles does not rule out varicella as a diagnosis.
^bPCR of scabs or vesicular fluid is the preferred method for laboratory confirmation of varicella. In the absence of vesicles or scabs, scrapings of maculopapular lesions can be collected for testing
^cNot explained by varicella vaccination during the previous 6-45 days.
^dSeroconversion is defined as a negative serum VZV IgG followed by a positive serum VZV IgG.
^eIn vaccinated persons, a 4-fold rise may not occur.
^fIgM serology has limited value as a diagnostic method for VZV infection and is not recommended for laboratory confirmation of varicella. However, an IgM positive result in the presence of varicella-like symptoms can indicate a likely acute VZV infection. A positive IgM result in the absence of clinical disease is not considered indicative of active varicella.

A3. Epidemiologic Linkage Criteria

Confirmatory Epidemiologic Linkage Evidence:

Exposure to or contact with a laboratory-confirmed varicella case, OR
Can be linked to a varicella cluster or outbreak containing ≥1 laboratory-confirmed case, OR
Exposure to or contact with a person with herpes zoster (regardless of laboratory confirmation).

Presumptive Epidemiologic Linkage Evidence:

Exposure to or contact with a probable varicella case that had a generalized rash with vesicles.

A4. Healthcare Record Criteria

Provider diagnosis of varicella or chickenpox but no rash description.

A5. Case Classifications

Confirmed:

Meets clinical evidence AND confirmatory laboratory evidence,

Meets clinical evidence with a generalized rash with vesicles AND confirmatory epidemiologic linkage evidence.

Probable:

Meets clinical evidence with a generalized rash with vesicles,

Meets clinical evidence with a generalized rash without vesicles AND:
Confirmatory or presumptive epidemiologic linkage evidence, OR
Supportive laboratory evidence.

Meets healthcare record criteria AND:
Confirmatory or presumptive epidemiologic linkage evidence, OR
Confirmatory or supportive laboratory evidence.

B. Criteria to Distinguish a New Case of Varicella from Reports or Notifications which Should Not be Enumerated as a New Case for Surveillance

The following should be enumerated as a new case:

Person with a new onset of symptoms that meets the criteria for a confirmed or probable case,

Person was previously enumerated as a case followed by a documented period of recovery

AND

^**

Person was previously reported but not enumerated as a confirmed or probable case, then subsequently available information meets the criteria for a confirmed or probable case.

^**Varicella generally confers life-long protection. There have been reports of second episodes of varicella, but in most cases the first episode was not laboratory-confirmed.

Table VI. Table of criteria to determine whether a case should be reported to public health authorities.

Criterion	Varicella
Clinical Criteria for Reporting
An acute illness with a generalized rash with vesicles		N
An acute illness with a generalized rash without vesicles			N
Absence of a more likely alternative diagnosis*		N	N
Laboratory Criteria for Reporting^a
Positive polymerase chain reaction (PCR) for varicella-zoster virus (VZV) DNA^b,c	S
Positive direct fluorescent antibody (DFA) for VZV DNA	S
Isolation of VZV	S
Significant rise (i.e., at least a 4-fold rise or seroconversion^c,d) in paired acute and convalescent serum VZV immunoglobulin G (IgG) antibody^c,e	S
Epidemiologic Linkage Criteria for Reporting
Exposure to or contact with a varicella case, a person with herpes zoster, or a varicella cluster or outbreak within one incubation period before the rash onset			N
Vital Record Criteria for Reporting
A person whose death certificate lists varicella or chickenpox as an underlying cause of death or significant condition contributing to death	S
Healthcare Record Criteria for Reporting
A person whose healthcare record contains a diagnosis of varicella or chickenpox	S

Notes:

S = This criterion alone is SUFFICIENT to report a case.

N = All “N” criteria in the same column are NECESSARY to report a case.

^*Consider varicella when lesions in various stages of development are present at the same time.

^aa A negative laboratory result in a person with generalized rash with vesicles does not rule out varicella as a diagnosis.

^bPCR of scabs or vesicular fluid is the preferred method for laboratory confirmation of varicella. In the absence of vesicles or scabs, scrapings of maculopapular lesions can be collected for testing.

^cNot explained by varicella vaccination during the previous 6-45 days.

^dSeroconversion is defined as a negative serum VZV IgG followed by a positive serum VZV IgG.

^ePaired IgG acute- and convalescent-phase antibody tests are not practical for immediate clinical management. In vaccinated persons, a 4-fold rise may not occur.

Table VII.A. Classification Table: Criteria for defining a case of varicella.

Criterion	Confirmed		Probable
Clinical Evidence
An acute illness with a generalized rash with vesicles (maculopapulovesicular rash)	O	N	N
An acute illness with a generalized rash without vesicles (maculopapular rash)	O			N	N
Absence of a more likely alternative diagnosis	N	N	N	N	N
Laboratory Evidence^a
Positive polymerase chain reaction (PCR) for varicella-zoster virus (VZV) DNA^b,c	O						O
Positive direct fluorescent antibody (DFA) for VZV DNA	O						O
Isolation of VZV	O						O
Significant rise (i.e., at least a 4-fold rise or seroconversion^c,d) in paired acute and convalescent serum VZV immunoglobulin G (IgG) antibody^c,e	O						O
Positive test for serum VZV immunoglobulin M (IgM) antibody^c,f					N		O
Epidemiologic Linkage Evidence
Exposure to or contact with a laboratory-confirmed varicella case		O		O		O
Can be linked to a varicella cluster or outbreak containing ≥1 laboratory-confirmed case		O		O		O
Exposure to or contact with a person with herpes zoster (regardless of laboratory confirmation)		O		O		O
Exposure to or contact with a probable varicella case that had a generalized rash with vesicles				O		O
Healthcare Record Evidence
Provider diagnosis of varicella or chickenpox but no rash description						N	N

Notes:

N = All “N” criteria in the same column are NECESSARY to classify a case.

O = At least one of these “O” (ONE OR MORE) criteria in each category (categories=clinical evidence, laboratory evidence, and epidemiologic evidence) in the same column—in conjunction with all “N” criteria in the same column—is required to classify a case.

^a A negative laboratory result in a person with a generalized rash with vesicles does not rule out varicella as a diagnosis.

^b PCR of scabs or vesicular fluid is the preferred method for laboratory confirmation of varicella. In the absence of vesicles or scabs, scrapings of maculopapular lesions can be collected for testing.

^c Not explained by varicella vaccination during the previous 6-45 days.

^dSeroconversion is defined as a negative serum VZV IgG followed by a positive serum VZV IgG.

^eIn vaccinated persons, a 4-fold rise may not occur.

^f IgM serology has limited value as a diagnostic method for VZV infection and is not recommended for laboratory confirmation of varicella. However, an IgM positive result in the presence of varicella-like symptoms can indicate a likely acute VZV infection. A positive IgM result in the absence of clinical disease is not considered indicative of active varicella.

Table VII.B. Classification Table: Criteria to distinguish a new case of Varicella from reports or notifications which should not be enumerated as a new case for surveillance.

Criterion	Confirmed		Probable
Criteria to distinguish a new case
Person with new onset of symptoms that meets the criteria for a confirmed case.	S	N
Person with new onset of symptoms that meets the criteria for a probable case.			S	N
Person was previously enumerated as a case followed by a documented period of recovery AND newly meets the criteria for a confirmed or probable case		O		O
Person was previously reported but not enumerated as a confirmed or probable case, then subsequently available information meets the criteria for a confirmed or probable case		O		O

S = This criterion alone is SUFFICIENT to enumerate as a new case

N = All “N” criteria in the same column are NECESSARY to enumerate as a new case

O = At least one of these “O” (ONE OR MORE) criteria in the same column—in conjunction with all “N” criteria in the same column—is required to enumerate as a new case.

Date Posted: February 13, 2024

Updated: February 13, 2024