An epidemic of parvovirus B19 in a population of 3596 pregnant women: a study of sociodemographic and medical risk factors

Objectives To estimate the incidence of human parvovirus B 19 among pregnant women before and during an epidemic, to elucidate possible sociodemographic and medical risk factors during pregnancy and to estimate the association between parvovirus B19 infection and negative pregnancy outcome. Design Prospective study among pregnant women followed from their first antenatal visit before 24 full weeks of gestation until delivery. Setting Department of Obstetrics and Gynaecology, Odense University Hospital, Denmark, November 1992 to February 1994. Methods 3596 pregnant women were invited to participate. The women were examined at first antenatal visit in the period from November 1992 to February 1994 and at delivery. The last delivery was in August 1994 and samples were thus collected before and during a large parvovirus B19 epidemic in Denmark January to September 1994. A blood sample for parvovirus B19 serology was taken at enrolment and from the umbilical cord at delivery. Three questionnaires were completed during 2nd and 3rd trimesters and a registration form at delivery. In total, 3174 (87.6%) were enrolled and 79.5% completed the study. Results The prevalence of B 19 IgG seropositivity at the first antenatal Visit before 24 full weeks of gestation was 66%. The cumulative prevalence proportion of acute parvovirus B19 infection during pregnancy among IgG negative women was found to be 10.3% (IgM seropositivity and/or IgG seroconversion). The IgG seroconversion incidence increased significantly from 1.0% to 13.5% among 932 seronegative pregnant women before and during the epidemic, respectively (P < 0.001). Independent risk factors related to increased risk of B 19 infection during pregnancy, adjusted for other sociodemographic and medical factors, were: children at home (adjusted OR 2.1, 95 % CI 1.3-3.2); serious medical disease (adjusted OR 3.0, 95% CI 1.0-8.5); and a stressful job (adjusted OR 1.8, 95% CI 1.0-3.3). Parvovirus B19 IgM seropositivity was associated with events of late spontaneous abortions and stillbirths (crude OR 9.9; 95% CI 3.3-29.4). Conclusion Before and during an epidemic of acute B19 infection incidences were measured among pregnant women to be 1.0% and 13.5%, respectively. Three factors, significantly increasing the risk of acute B19, were identified as: having children at home; suffering from serious medical diseases; and having a stressful job. IgM positivity for parvovirus B19 was associated with negative outcome of pregnancy.