Clinical Presentation and Vaccination Status of Laboratory Confirmed PCR-Positive Varicella Cases Versus PCR- Negative Varicella Cases: A Comparison

Background:  Polymerase chain reaction (PCR) testing for varicella zoster virus (VZV) DNA is the most specific and sensitive test for VZV. Laboratory testing is essential in confirming diagnosis and understanding the changing clinical presentation of varicella.

Objectives:  To compare characteristics of PCR-positive versus PCR-negative varicella cases reported to VASP.

Methods:  A varicella case was defined as illness with acute onset of a diffuse papulovesicular rash without other known cause diagnosed by a healthcare provider (HCP), school nurse or parent.  Cases with onset from January 2003-November 2010 with PCR testing were analyzed.  Vaccination information was verified through HCP or school records.  Skin lesion specimens were collected from suspected cases within five days of rash onset and tested at CDC’s National VZV Laboratory.  Cases with inadequate specimens were excluded. 

Results:  232 /2,563 (9.1%) reported cases had PCR testing.  Of these, 145(62.5%) were PCR-positive and 26(11.2%) were PCR-negative.  Of the PCR-positive cases, 60(41.3%) were unvaccinated, 82(56.6%) had 1-dose, and 3(2.1%) had 2-doses of varicella vaccine.  Of the PCR-negative cases, 2(7.7%) were unvaccinated, 22(84.6%) had 1-dose and 2(7.7%) had 2-doses.  Fewer PCR-positive cases had <50 lesions compared to PCR-negative cases (38.6% vs. 76.9%).  A greater proportion of PCR-positive cases had 50-250 lesions compared to PCR-negative cases, (45.5% vs. 15.4%). PCR-positive cases had a smaller proportion of macular/papular lesions (62.1% vs. 80.8%) and a larger proportion of vesicular cases (35.2% vs.15.4%) when compared to PCR-negative cases.  A greater proportion of PCR-negative cases had received 2 doses compared PCR positive cases (7.7% vs. 2.1%).

Conclusions:  PCR-negative cases had milder clinical presentations compared to PCR-positive cases.  For PCR-negative cases, the rash may be attributable to other etiologies.  It is important to continue PCR testing to confirm suspected varicella cases and to test for other common childhood viruses in PCR-negative cases.