Clinical Presentation of Varicella-Zoster Virus
The Council of State and Territorial Epidemiologists (CSTE)-approved varicella case definition describes varicella as an illness with acute onset of diffuse (generalized) maculopapulovesicular rash without other apparent cause. Varicella is seen primarily in children younger than 10 years. The CDC provides additional information about classic symptoms of varicella.
Shingles (Herpes Zoster)
Herpes zoster generally presents as a painful, itchy, or tingly rash in one or two adjacent dermatomes (localized zoster). Herpes zoster is most common in patients older than 50 years. The most common location is in the thoracic dermatome. Rashes generally do not cross the body’s midline. The CDC provides additional information about classic symptoms of herpes zoster.
Indications for Testing
Classic Varicella-Zoster Virus Presentation
Laboratory testing is generally not necessary or recommended for persons who exhibit canonical presentation of VZV infections. Classic presentations of varicella and herpes zoster virus are described by the CDC.
Suspected Chickenpox (Varicella)
If clinical features alone are not confirmatory, especially in patients who have received one or both of the CDC-recommended varicella vaccination doses, laboratory testing is recommended to confirm diagnosis.
Suspected Shingles (Herpes Zoster)
If clinical features alone are not confirmatory, especially in patients who have received the recommended vaccination for shingles and in people with suppressed immune systems, laboratory testing is recommended to confirm diagnosis.
Suspected Vaccine-Related Event
If a patient is experiencing adverse effects after vaccination, laboratory testing can be performed to detect possible VZV infection and to determine whether complications are due to a VZV vaccine strain.
Laboratory testing may also be appropriate to investigate outbreaks, unusual cases, or severe cases involving hospitalization or death. Previous immunization status may also be investigated using serology.
Polymerase Chain Reaction
PCR is the most rapid and sensitive method for confirming a diagnosis of varicella or herpes zoster. As such, it is the preferred test for VZV infection. If present, vesicular lesions or scabs provide the best samples for PCR analysis. In their absence, other sample types such as cerebrospinal fluid (CSF), saliva, or blood may be used, but alternate sample types are associated with an increased risk of false-negative results.
PCR genotyping (not performed at ARUP Laboratories) is useful to identify vaccine-specific VZV strains for the identification or confirmation of adverse vaccination reactions. The recommended sample type for VZV PCR genotyping is tissue from a vesicular lesion. Blood, CSF, or biopsy specimens may also be used but increase the risk of false-negative results.
The CDC provides more information about best practices for sample collection on their website.
Other Testing (Useful Only in Certain Situations)
Direct Fluorescent Antibody Stains
PCR is preferred to DFA stains. DFA testing is limited by the sample quality and has generally low sensitivity. If insufficient infected cells are present, the results may be invalid or falsely negative. Confirmation with PCR or viral culture may be necessary.
Serology has limited utility for laboratory diagnosis of VZV and should only be used when suitable specimens for PCR testing are not available.
Viral culture of VZV is not recommended for initial diagnosis because its slow turnaround time may adversely impact clinical management. Culture may be used to confirm DFA results.
Serology can be used to determine a patient’s immunization status and inform future vaccination schedules. Please see the Immunization Status ARUP Consult topic for more information.