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 pregnan t women before and during an epidemic, to elucidate possible sociodemograph ic and medical risk factors during pregnancy and to estimate the associatio n between parvovirus B19 infection and negative pregnancy outcome. Design Prospective study among pregnant women followed from their first ant enatal visit before 24 full weeks of gestation until delivery. Setting Department of Obstetrics and Gynaecology, Odense University Hospita l, Denmark, November 1992 to February 1994. Methods 3596 pregnant women were invited to participate. The women were exa mined 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 wer e thus collected before and during a large parvovirus B19 epidemic in Denma rk January to September 1994. A blood sample for parvovirus B19 serology wa s taken at enrolment and from the umbilical cord at delivery. Three questio nnaires were completed during 2nd and 3rd trimesters and a registration for m 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 Vi sit before 24 full weeks of gestation was 66%. The cumulative prevalence pr oportion of acute parvovirus B19 infection during pregnancy among IgG negat ive women was found to be 10.3% (IgM seropositivity and/or IgG seroconversi on). 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 ri sk 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 stres sful job (adjusted OR 1.8, 95% CI 1.0-3.3). Parvovirus B19 IgM seropositivi ty 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. Thre e factors, significantly increasing the risk of acute B19, were identified as: having children at home; suffering from serious medical diseases; and h aving a stressful job. IgM positivity for parvovirus B19 was associated wit h negative outcome of pregnancy.