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.
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.
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. 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. PCR testing 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.
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. DFA testing is limited by the sample quality and has generally low sensitivity. If an insufficient number of infected cells is present, the results may be invalid or falsely negative.
Confirmation with PCR testing 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.
Rapid diagnostic test with reflex to culture; may help to determine whether a lesion is due to VZV or herpes simplex virus HSV. Refer to the Immunization Status topic for more information. Evaluation of laboratory methods for diagnosis of varicella. Clin Infect Dis. Chickenpox varicella : interpreting laboratory tests. Gnann JW. Transport media Specimens may be shipped dry, without transport media. Containers appropriate for specimen Vesicular fluid — put swab in a tube, dry.
Swab tube, dry. Sterile screw-capped vials. Slides in sturdy cardboard container. Storage and shipping temperature Dry specimens: room temperature. Turnaround time for PCR results is typically 2 business days after receipt of specimen s.
Paired acute and convalescent sera showing a four-fold rise in IgG antibodies have excellent specificity for varicella, but are not as sensitive as PCR of skin lesions for diagnosing varicella. People with prior history of vaccination or disease history may have very high baseline titers, and may not achieve a four-fold increase in the convalescent sera.
The usefulness of this method for diagnosing varicella is further limited as it requires two office visits. For both unvaccinated and vaccinated people, PCR is the most reliable method for confirming infection. Examples of possible varicella vaccine-adverse events for which PCR genotyping for VZV can be useful include varicella or a varicella-related complication in a vaccinated person 7 to 42 days after vaccination, herpes zoster in a vaccinated person, and suspected secondary vaccine-strain VZV transmission.
A single serologic IgG test can be used to determine if a person has antibodies to VZV from past varicella disease or who may be candidates for varicella-zoster immune globulin VZIG. The product available in the U. It can readily detect seroconversion to natural infection with VZV. Routine testing for varicella immunity following vaccination is not recommended because commercially available VZV IgG assays are not sensitive enough to detect all seroconversions after vaccination.
IgG avidity has been used in research settings to determine if a person who is IgG positive for VZV was infected with the virus in the past or more recently. The laboratory at CDC has developed an IgG avidity assay which can be used to determine if the most recent VZV rash was due to primary infection varicella or reactivation herpes zoster. Immunity post infection is usually lifelong though the latent virus inhabits the sensory nerve ganglia where it can reactivate causing shingles when immunity declines with aging.
The patterns of polymorphisms in VZV correlate with different geographical regions of infection and is the basis for the classification of viral clades.
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