Parvovirus B19: how to interpret semi-quantitative viraemia values during high circulation of the virus in the...

To establish the correct diagnosis of the disease. To interpret the results of semi-quantitative viraemia testing. To evaluate the clinical and laboratory course of the disease.

At the Department of Infectious Diseases of the University Hospital of Hradec Králové and the Faculty of Medicine of Charles University, patients (n = 18) with parvovirus B19 infection were retrospectively studied for the period from March 1 to June 30, 2024. Their clinical condition, viraemia levels, and routine laboratory haematological and biochemical data were monitored.

Viraemia levels ranged from 105 to 1011 copies/ml. Levels below 107 copies/ml were detected in patients with symptoms persisting for more than a week or considered as complications of the infection. In addition to exanthema and fever, the clinical course was characterised by pharyngitis, headache, vomiting in young children, arthralgia in adults, and, surprisingly, abdominal pain, meningism, hepatopathy with conjugated hyperbilirubinemia, and anaemic syndrome. Most adult patients had leukopenia, some with concomitant thrombocytopenia, but always with spontaneous resolution within eight days without complications. Such changes in blood counts were not observed in paediatric patients.

To diagnose parvovirus B19 infection, it is important to know the possible clinical courses and typical laboratory findings, to have access to rapid PCR testing with quantitative viraemia values, and to be able to interpret these data. We consider viraemia levels of 10⁷ copies/ml and above within a week of the onset of symptoms to confirm the diagnosis. Lower values need to be interpreted with caution. Based on the duration of symptoms and clinical course, we can consider an immunopathological reaction caused by parvovirus B19 or an incidental finding of viraemia in another diagnosis, especially when there is a high circulation of the virus in the population.