Interpretive Handbook

Varicella-zoster virus (VZV), a herpesvirus, causes 2 exanthematous (rash-associated) diseases: chickenpox and herpes zoster (shingles). Chickenpox is a highly contagious disease usually contracted during childhood and is characterized by a dermal vesiculopustular rash that develops in successive crops. Although primary infection results in immunity to subsequent exposure to chickenpox, the virus remains latent in the body, localized to the dorsal root or cranial nerve ganglia. Reactivation of latent infection manifests as herpes zoster. On reactivation, the virus migrates along neural pathways to the skin, producing a unilateral rash usually limited to a single dermatome. Reactivation occurs in older adults and in patients with impaired cellular immunity.

Several populations are at risk of suffering an unusually severe reaction to VZV infections. The infection in pregnant women may spread through the placenta to the fetus, causing congenital disease in the infant. Immunocompromised patients in hospitals may contract severe nosocomial infections from others who have active VZV infections. Therefore, serologic screening of direct health care providers (physicians, allied health care personnel) and individuals in high-risk groups is necessary to avoid uncontrolled spread of infection.

While the clinical presentation of VZV infection is generally characteristic, serologic evaluation of patients with atypical and systemic infections is often required. For example, it is extremely important to serologically evaluate patients for the early detection of VZV infections in hospital settings. Nosocomial spread of VZV infection can be life-threatening to immunocompromised patients susceptible to infection.

Diagnosing acute-phase infection with varicella-zoster virus

A positive IgG result coupled with a positive IgM result indicates recent infection with varicella-zoster virus (VZV).

A positive IgG result coupled with a negative IgM result indicates previous exposure to VZV and immunity.

A negative IgG result coupled with a negative IgM result indicates the absence of prior exposure to VZV and nonimmunity. However, a negative result does not rule out a VZV infection. The specimen may have been drawn before the appearance of detectable antibodies. Negative results in suspected early VZV infections should be followed by testing a new serum specimen in 2 to 3 weeks.

Equivocal results should be followed up with testing a new serum specimen within 10 to 14 days.

The performance characteristics with individuals vaccinated with varicella-zoster virus (VZV) (OKA Strain) have not been established.

The test must be performed on serum. The use of whole blood, plasma, or cord blood has not been established.

Positive results from cord blood or neonates should be interpreted with caution.

Results from immunocompromised patients should be interpreted with caution.

Heterotypic antibody titer rises in response to VZV may occur in certain patients with herpes simplex virus infection who have experienced a prior infection with VZV.

IgG

Negative (reported as positive or negative)

A negative result indicates nonimmunity.

IgM

Negative (reported as positive or negative)

1. Kennedy PG: Latent varicella-zoster virus is located predominantly in neurons in human trigeminal ganglia. Proc Natl Acad Sci USA 1998;95:4658-4662

2. McPherson RE: Herpes zoster ophthalmicus and the immunocompromised host: a case report and review. J Am Optom Assoc 1997;68:527-538

3. Papanicolaou GA, Meyers BR, Fuchs WS, et al: Infectious ocular complications in orthotopic liver transplant patients. Clin Infect Dis 1997;24:1172-1177

4. Flamholc L: Neurological complications in herpes zoster. Scand J Infect Dis 1996;100:35-40