Varicella Zoster Serology

Diagnostic Use

Serology is most useful for determining whether a patient, health care worker or pregnant women is susceptible to VZV infection. Antibody to VZV develops within a few days after onset of varicella and persists for many years. Persistence of VZV antibodies beyond 8 months of age is suggestive of intrauterine varicella. Commercial EIA kits may fail to identify individuals who have been immunized with VZV vaccine.

Interpretation

Varicella Zoster Virus serology

For investigation of a vesicular rash, use a viral swab to collect vesicle fluid and scrape base of vesicle (see VZV PCR).
Serology is most useful for determining whether a patient, health care worker or pregnant women is susceptible to VZV infection. Antibody to VZV develops within a few days after onset of varicella and persists for many years. Persistence of VZV antibodies beyond 8 months of age is suggestive of intrauterine varicella. Commercial EIA kits may fail to identify individuals who have been immunized with VZV vaccine.

Chickenpox is highly contagious with secondary household attack rates of > 90% in susceptible individuals. The clinical manifestations of chickenpox typically include a prodrome of fever, malaise, followed by the development of a generalized vesicular rash, usually within 24 hours. The lesions appear as successive crops of vesicles appearing first on the face and scalp, later spreading to the trunk, abdomen and limbs over a 3-4 day period. Most lesions have fully crusted by day 6 in normal hosts.

Complications include bacterial superinfection of skin lesions, varicella pneumonitis, acute cerebellar ataxia and rarely encephalitis.

Incubation period: 14-16 days (range 10-21; up to 28 days if VZIG received).
Infectious period: from 1-2 days before the rash until the lesions have crusted.

Susceptible health care workers exposed to chickenpox or shingles should be removed from patient contact from day 10-21 after exposure to an infectious patient. Please advise patients with chickenpox not to visit others in hospital or susceptible immunocompromised or pregnant contacts until they are no longer infectious.

Exposure to or development of chickenpox during pregnancy: If a pregnant woman is exposed to chickenpox or shingles and is unsure whether she has had chickenpox in the past, she should be tested for VZV IgG as soon as possible. If the woman is already known to be susceptible or VZV IgG subsequently returns negative, they should be offered zoster immunoglobulin (ZIG) preferably as soon as possible but up to 10 days after contact. Zoster immunoglobulin may not prevent infection but reduces illness severity. If more than 10 days has elapsed since the contact, prophylactic acyclovir may be considered from day 10 after contact. Given during the incubation period or within 24 hours of rash onset, it can reduce risk of infection or illness duration and severity. Foetal infection occurs in 10-15% of cases of chickenpox in pregnant women but is usually asymptomatic. However, approximately 2% of infants of woman who have chickenpox at 12-20 weeks gestation develop foetal varicella syndrome. Maternal varicella developing within 5 days before to 2 days after delivery can cause severe varicella in the neonate and therefore zoster immunoglobulin is given to the infant immediately after delivery or as soon as the mother develops a rash.

Zoster immunoglobulin is a blood product provided by the New Zealand Blood Service. Supplies are kept in the Blood Bank. Supplies of suitable plasma for Zoster Immunoglobulin production are scarce. Healthy adults recovering from shingles or chickenpox should be encouraged to enroll as voluntary blood donors.

VZV vaccine should be considered for post-exposure prophylaxis in non-pregnant adults and children. When given to susceptible people, within 3-5 days of exposure, it may prevent or modify disease. For further information on its use refer to the current Immunisation handbook under “Immunisation” at www.moh.govt.nz/healthtopics

For further information about airborne precautions, refer to the Infection Prevention & Control service.

Reference Intervals

Comment will be made on immune status