We developed and validated a sensitive and specific rapid HSV real-time PCR assay procedure that can be performed in 2 hours from receipt of sample to result reporting. By using the automatic extraction machine, pre-packed nuclear acid extraction reagents, and premixed and pre-aliquot PCR reagents, the procedure is self contained and can be performed in a regular laboratory by technologists with very little PCR training. Although the procedure is not performed by the clinical staff within the vicinity of the patients as other point of care (POC) devices, as defined by CAP, the procedure is a useful POC alternative since the technique is easy and fast, and the assay is sensitive and specific.
Weighing the consequences of a false positive, which may potentially expose the patient to unnecessary interventions, and a false negative, which may result in transmission of neonatal HSV, we determined that positivity in both wells maximized specificity and low copy number cut-off maximized sensitivity. The threshold amount of virus that may result in transmission is unknown; however, we have reported transmission of culture negative, PCR positive cases at between 500 – 1000 copies of DNA/swab sample in our standard TaqMan assay (1
Ideally, a rapid test for HSV detection in labor should be combined with a serologic test for HSV-2 antibodies. Those women who lack HSV-2 antibodies but are shedding HSV at the time of labor are a very high risk (30–50%) of transmitting the infection to their neonate (1
). In this situation, caesarean delivery is appropriate, and some experts would also administer acyclovir to the neonate, especially if the membranes were ruptured (13
). The risk of HSV transmission to the neonate is much lower if the woman has antibodies to HSV-2 and the infant is exposed to HSV at the time of delivery. A course of intrapartum acyclovir may reduce further the already low risk of neonatal infection. Our approach would parallel the successful strategies for Group B streptococcus prevention (14
) and HIV prevention (15), in which providing the infant with pre-exposure prophylaxis with an antibiotic or an antiviral prevents the pathogen from establishing productive infection. In animal models, preloading mice with acyclovir prior to HSV exposure prevents infection (16
), although the relevance of these models to human HSV infection is unclear. Our rapid assay was developed as a tool to help organize scientific evaluations to define how best to manage infants exposed to HSV at delivery.
Our approach uses a type-common probe. Although type-specific PCR assays have been developed, they may be somewhat less sensitive (17
), and it is not clear that such are needed for this use. Women who have HSV-2 detected in the genital tract are at high risk for infecting their infant if they are seronegative and experiencing a new HSV infection. In contrast, women who have HSV-1 detected in the genital tract are at high risk for infecting their infants regardless whether they have new HSV-1 infection or reactivation of HSV-1 (1
). As such, detection of HSV in the genital tract during labor, combined with a negative serologic test for HSV-2, represents a high risk scenario regardless whether the virus detected is HSV-1 or HSV-2. In contrast, women who are HSV-2 seropositive and are shedding HSV in labor are at low, albeit not absent risk.
Studies that have evaluated the interest of women in being tested for HSV during pregnancy suggest that women are willing, and that some expect it as part of the routine care (21, 22). Even when asked specifically about a hypothetical HSV test that would be administered during labor, 85% of women expressed interest (18
). While theoretical agreement to testing may not always correspond to consent for actual testing, experience at our institution where HSV antibody testing has been incorporated into routine prenatal care suggest that women rarely object to this test, which is similar to the high acceptability of HIV testing when incorporated into routine medical care for pregnant women (19
). Concerns about routine serologic testing for HSV have been raised, both from the point of view of shortcomings of the commercially available serologic assays, as well as cost-benefit calculations. The use of rapid PCR for HSV in labor can obviate some of these concerns because only women who are HSV PCR positive need to be tested for HSV-2 antibody, and rapid bedside antibody tests are commercially available (25, 26).
In summary, we have developed a rapid test for HSV in genital secretions that can be resulted within 2 hours, a time frame that allows the physician to institute appropriate interventions to reduce the risk of HSV transmission to the neonate. While the technical development of this test needs to be followed by clinical studies among pregnant women, and appropriate management strategies for women who are HSV positive in labor need to be evaluated, we hope that this tool will allow clinical studies to be conducted toward defining effective strategies for reducing the burden of neonatal HSV in the United States.