PCR Testing for Herpes Simplex Virus and Varicella-Zoster Virus

Polymerase chain reaction (PCR) testing for herpes simplex virus (HSV) and varicella-zoster virus (VZV) have become the standard of practice for evaluating patients with viral encephalitis and meningitis (1, 2). Common wisdom suggests that most cutaneous HSV and VZV infections can be diagnosed clinically. However there are a number of situations where specific tests are helpful. Laboratory confirmation of HSV and VZV infection helps to exclude other illnesses, may allay anxiety, and guides counseling and treatment.

Practical examples of the value of confirmatory treatment include the diagnosis of genital herpes and the evaluation of zosteriform eruptions. A diagnosis of genital herpes often implies recurrent discomfort for the patient and can contribute to chronic psychological and social distress. This diagnosis also may require behavioral modifications and acyclovir treatment (3). Empirical diagnosis without laboratory confirmation may cause unwarranted problems for the patient (CDC).

Another example of the value of laboratory testing is in the evaluation of recurring zosteriform eruptions. These lesions are frequently misdiagnosed as recurring VZV outbreaks rather than recurring cutaneous HSV infections (4, 5). Timely confirmation of these infections will avoid the hazards and expense of ceaseless empiricism (4).

Laboratory confirmation of cutaneous HSV and VZV infections are traditionally done by culture and/or direct fluorescent antibody (DFA) methods. Due to the nature of the test, culture methods do not provide confirmatory information in time to guide therapy or allay patient anxieties. DFA testing of a well-collected swab specimen can provide a timely (next day) answer but DFA methods can only be done on limited specimen types. Real-time PCR testing is increasingly used for laboratory confirmation of HSV and VZV infection because of its rapid turnaround time and the wide range of specimens that can be tested.

Advantages of PCR Testing

Increased sensitivity. Numerous studies have shown that PCR testing for HSV and VZV is more sensitive than culture and direct fluorescent antibody testing combined. PCR produces fewer false negative results because the specimen does not have to be alive when it arrives in the laboratory.

Faster time to result. The turnaround times for an HSV culture are 2 days for an early positive result and 8 days for a final negative result. VZV turnaround times are 3 days for an early positive result and 6 days for a final negative result. DFA testing results are available the next day. PCR testing is done daily. Specimens that arrive in the lab tonight will be resulted the next day.

Wider range of specimen types than DFA. PCR testing can be done on lesion swabs submitted in M4 viral transport medium, cerebrospinal fluid, broncheoalveolar lavage specimens, ocular fluids amniotic fluids, vesicle fluids, corneal scrapings, and tissues. DFA testing is only done be done on BAL specimens and lesion swabs submitted in M4 viral transport media.

Robust specimen transport conditions. PCR specimens can be transported at room temperature. Warde Medical Laboratory recommends refrigerated transport to allow culture and DFA to be done on the same specimen, but the laboratory will not reject PCR specimens transported at room temperature.

HSV typing. The HSVPCR test does not differentiate HSV 1 from HSV 2. However, HSV typing (HSVT) can be ordered on PCR-positive specimens. HSV typing is also available on culture isolates (HVT) and DFA specimens (HST).