Seroprevalence of human granulocytic ehrlichiosis in high-risk groups in Denmark

The aim of this study was to evaluate the seroprevalence of human granulocytic ehrlichiosis (HGE) among 300 residents in the county of Funen, Denmark. All of these people had either suspected or confirmed borreliosis. Two hundred control sera were included in the study. Samples were submitted by general practitioners and by hospital departments. An indirect immunofluorescence assay was used to identify sera reactive to HGE and an enzyme-linked immunosorbent assay was used to analyse Borrelia burgdorferi antibodies. There were 63 (21%) HGE-positive sera, 53 of which came from Borrelia-seropositive patients. Among patients with negative Borrelia serology, but with clinical suspicion of borreliosis, 14.3% were HGE-positive (n = 70). Of the 200 control sera, 3.5% were HGE-positive and 10.5% were Borrelia-positive. No HGE-positive samples were found among subjects < 20 y of age, wheras 20.4% of Borrelia seropositive samples where from subjects < 20 y of age. No mortality was observed in the HGE-positive group and the percentage of serum samples positive for both Borrelia and HGE did not differ significantly between hospitalized and non-hospitalized patients. Our study indicates that HGE infection with or without concomitant or previous Borrelia burgdorferi infection is common in tick-exposed individuals > 20 y old in the county of Funen, Denmark.