Risk Factors for Herpes Simplex Virus Transmission to Pregnant Women: A Couples Study

Abstract

An estimated 60% to 80% of neonatal herpes simplex virus (HSV) infections are a result of the mother acquiring HSV-1 or HSV-2 close to the time of delivery. Although it is relatively uncommon for HSV to be acquired at the end of pregnancy, transmission takes place efficiently. This suggests that preventing maternal acquisition of HSV during pregnancy may effectively lower the risk of neonatal infection. This couples study was done to identify risk factors for acquiring HSV in at-risk pregnant women who were participating in a prospective study of HSV in pregnancy. They invited their partners to undergo serologic testing for type-specific HSV. A total of 3192 couples took part in the study. Serum samples were taken at the initial prenatal visit and again at the time of labor, and swabs were taken at labor from the external genitalia and cervix. Antibodies to HSV-1 and HSV-2 were sought by the Western blot technique. Just over one fifth of women in the study were at risk of acquiring HSV. Of 582 who were seronegative for HSV-1 and whose partners were seropositive, 14 (3.5% when adjusted for gestational length) did acquire HSV-1. Having a partner with a history of oral herpes correlated with acquisition of HSV-1 (odds ratio [OR] 8.1; 95% confidence interval [CI], 1.8-36) and accounted for three fourths of incident infections. Of 125 women at risk for acquiring HSV-2, 17 (20% when adjusted for gestational length) became infected. Partnership for 12 months or less correlated with acquiring HSV-2 (OR, 7.8; 95% CI, 2.3-25.7) and accounted for 63% of incident infections. The presence of HSV-1 antibodies did not influence the rate of acquiring HSV-2 to any substantial degree. The rate of subclinical infection in 31 women who acquired HSV from their partners during pregnancy was 68%. The rate did not depend on whether the women acquired HSV-1 or HSV-2. There was a single case of neonatal herpes. No set of clinical features was found that identified a majority of susceptible women having serologically discordant partners. These findings imply that serologic screening may be necessary to identify women who are at risk of acquiring HSV while pregnant. Acquisition rates, especially those for HSV-2, are high for serologically discordant couples. Further studies are needed to determine the cost of serologically screening pregnant women and to what degree this practice will prevent maternal and neonatal HSV infections.