Coxiella burnetii infection among blood donors during the 2009 Q-fever outbreak in The Netherlands

BACKGROUND: In 2007, 2008, and 2009 outbreaks of Q‐fever occurred in the Netherlands with increasing magnitude. The 2009 outbreak with 2354 reported cases is the largest human Q‐fever outbreak ever recorded. To assess the extent of infection and the safety of donated blood, we tested local blood donations for presence of Coxiella burnetii antibodies and DNA. STUDY DESIGN AND METHODS: Starting May 2009, more than 40,000 serum samples were collected from all consenting blood donors in the areas with high Q‐fever incidence. The 1004 samples from the areas with the highest number of reported cases were tested for C. burnetii DNA by polymerase chain reaction; seroprevalence and incidence were determined using enzyme‐linked immunosorbent assay and immunofluorescence assays (IFAs) in the subset of 543 donors of whom a follow‐up sample was available. RESULTS: A total of 6 of 1004 donor samples tested reactive for C. burnetii DNA. Confirmatory testing (IFA) on the index and follow‐up samples demonstrated seroconversion in two donors, high‐level preexisting antibodies in one donor, and no seroconversion in three donors. Immunoglobulin (Ig)G testing of the 543 serum pairs showed that 66 were reactive in the latest sample, of which 10 represented seroconversions. CONCLUSION: In the area with highest incidence during a large Q‐fever outbreak, 3 of 1004 blood donations contained C. burnetii DNA (0.3%; 95% confidence interval, 0.1%‐1.0%). A total of 66 of 543 (12.2%) donors tested positive for anti‐Coxiella IgG. Ten seroconversions were detected, resulting in an incidence of 5.7% per year, which is more than 10‐fold higher than the local number of reported clinical cases (0.47% per year). [Correction added after online publication 14‐Jul‐11: high‐level existing antibodies has been updated to highlevel preexisting antibodies.]