Background: In the diagnosis of parvovirus B19 infection, the detection of virus-specific IgG in the absence of virus-specific IgM is considered to indicate past immunity.
Methods: We determined the diagnostic value of a high-quality B19 IgM EIA, compared with that of a VP1 IgG avidity EIA, a VP2 IgG epitope-type specificity (ETS) EIA, and real-time polymerase chain reaction (PCR) in the diagnosis of maternal B19 infection during nonimmune fetal hydrops.
Results: Serum samples from 101 pregnant women with confirmed B19-induced fetal hydrops were collected at the time of invasive prenatal diagnosis. The samples were investigated for B19 IgM, VP1 IgG avidity, and VP2 IgG ETS. With the B19 IgM EIA, 78 women (77.2 %) showed positive results, 15 (14.9%) showed negative results, and 8 (7.9 %) showed equivocal results. According to the combined B19 IgG avidity and IgG ETS EIA results, only 5 (5%) of 101 women were classified as having past immunity. Available serum samples (n = 24) that had nondiagnostic results in the antibody assays were further investigated by PCR. All were B19 DNA positive (mean load, 2.5 x 10(4) genome equivalents/mL; range, 2.5 x 10(3) - 7.8 x 10(6)).
Conclusions: At the time of B19-induced hydrops, detection of B19 DNA in maternal blood had the best diagnostic sensitivity for identifying maternal B19 infection. However, given the long persistence of B19 DNAemia, supplementary measurement of VP1 IgG avidity and VP2 IgG ETS improves the precision of diagnosis and management of pregnant women affected by the B19 virus.