Background: Although parvovirus infections are usually benign and self-limiting, it is important to confirm the diagnosis in a public health setting which might involve pregnant women and in which an outbreak could lead to medical consequences. In these situations, microbiological confirmation by thumb prick is a relatively low-invasive method that is simple to carry out.
Objective and study design: Because relatively small blood volumes are obtained in thumb prick blood samples, we compared the results of two different techniques during an outbreak of erythema infectiosum: the usual serological detection of IgM antibodies (ELISA) versus PCR-based detection of viral DNA.
Results: In a school-based outbreak, 39 cases (33 schoolchildren, three parents, three pre-schoolers) were registered over a period of 11 weeks. Sera were obtained from 23 of the school cases and two of the three parent cases. Of all thumb prick serum samples, 65% (15/23) tested positive or borderline positive for parvovirus IgM with ELISA, while 70% (16/23) tested positive or borderline positive with PCR. Although the overlap between the two tests was large (11 samples tested positive or borderline positive in both), a substantial number of samples showed contradictory results (nine samples).
Conclusion: The overall picture of 37 clinical cases of erythema infectiosum and two adult cases with arthritis, linked to a primary school, fits in well with positive diagnostic results by either technique for parvovirus B19, convincingly demonstrating an outbreak of fifth disease. The considerable number of discrepancies in sample results demonstrates that maximum sensitivity of parvovirus testing would require both tests to be performed.