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Conducting Varicella Surveillance

Varicella surveillance data are needed to

  • document and monitor the impact of the varicella vaccination program on varicella incidence, morbidity, and mortality,
  • evaluate the effectiveness of prevention strategies, and
  • evaluate vaccine effectiveness under conditions of routine use.

Varicella Reporting

Case Reporting

In 2002, Council of State and Territorial Epidemiologists (CSTE) recommended that varicella be included in NNDSS. All states are encouraged to conduct ongoing varicella surveillance to monitor vaccine impact on morbidity. States are encouraged to report varicella cases to NNDSS via the National Electronic Telecommunications Surveillance System (NETSS) or the National Electronic Disease Surveillance System (NEDSS).

As of 2010, 36 states have been conducting case-based varicella surveillance. For state-specific reporting requirements, contact the state health department. Information can also be found on CSTE's web site on state reportable conditions.

Case Definition

The following varicella case definitions were approved by CSTE in June 1999 and updated in June 2009. Case definitions for varicella cases and deaths can be found on CDC's web site on Nationally Notifiable Diseases Surveillance System.

Varicella Clinical Case Definition

An illness with acute onset of diffuse (generalized) maculopapulovesicular rash without other apparent cause. In vaccinated persons who develop varicella more than 42 days after vaccination (breakthrough disease), the disease is usually mild with fewer than 50 skin lesions and shorter duration of illness. The rash may also be atypical in appearance (maculopapular with few or no vesicles).

Laboratory Criteria for Diagnosis

  • Isolation of varicella-zoster virus (VZV) from a clinical specimen
  • Detection of VZV DNA by direct fluorescent antibody (DFA) or by polymerase chain reaction (PCR) tests from a clinical specimen, ideally scabs, vesicular fluid, or cells from the base of a lesion (For more information, see Laboratory Testing) These tests are also useful for diagnosing breakthrough disease.
  • Fourfold or greater rise in serum varicella IgG antibody titer by any standard serologic assay

For both unvaccinated and vaccinated persons, DNA detection methods (PCR, DFA) and culture are the methods of choice for laboratory confirmation. Of these, PCR is the most reliable method for confirming infection.

In unvaccinated persons, experience is limited with IgM antibody tests and with timing of the IgM response. In vaccinated persons, even less experience with serologic methods for laboratory confirmation is available. Therefore, DNA detection methods are the laboratory methods of choice for diagnosis. A negative IgM result should not be used to rule out the diagnosis. A positive IgM in the absence of rash should not be used to confirm a diagnosis.

A fourfold rise in IgG antibody may not occur in vaccinated persons.

For more information, see Interpreting Laboratory Tests.

Varicella Case Classification

Probable: A case that meets the clinical case definition but is not laboratory confirmed nor epidemiologically linked to another probable or confirmed case

Confirmed: A case that is laboratory confirmed or that meets the clinical case definition and is epidemiologically linked to a confirmed or a probable case

Note: Two probable cases that are epidemiologically linked are considered confirmed, even in the absence of laboratory confirmation.

Varicella Deaths

In 1998, CSTE recommended that varicella-related deaths be placed under national surveillance. As of January 1, 1999, varicella-related deaths became nationally notifiable to CDC.

Varicella deaths can be identified through death certificates, which may be available through state vital records systems. In states using electronic records, certificates may be more readily available soon after a person dies. State health departments may also request that local health departments, health care providers, and hospitals report varicella deaths that occur in their community.

Since varicella is preventable with vaccine, all deaths due to varicella should be investigated. Investigations may provide insight into risk factors for varicella mortality and may help identify missed opportunities for and barriers to vaccination. (For guidance on varicella death investigations, see the Varicella Death Investigation Worksheet [4 pages].)

Deaths should be reported to the Epidemiology Branch in the Division of Viral Diseases at CDC (404/639-8230) and to NNDSS via the NETSS or NEDSS.

The following case definitions for varicella deaths were approved by CSTE in 1998.

Varicella Deaths Case Classification

Probable: A probable case of varicella that contributes directly or indirectly to acute medical complications that result in death

Confirmed: A confirmed case of varicella that contributes directly or indirectly to acute medical complications that result in death


Resources for Varicella Surveillance


References

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