Hypophosphatemia, fever and prolonged length of hospital stay in seronegative PCR positive patients as compared to seropositive patients with early acute Q fever pneumonia

Background: Query fever (Q fever) is a zoonotic infection, caused by the intracellular Gram-negative coccobacillus Coxiella burnetii. From 2007 until 2010, a large Q fever outbreak has occurred in the Netherlands. We studied traditional and less common inflammation markers in seronegative and seropositive patients with acute Q fever pneumonia to identify markers that distinguish different disease stages and predict disease severity. Methods: A total of 443 adult patients presenting at the Emergency Department with community-acquired pneumonia were included in a prospective etiologic study. Patients with acute Q fever pneumonia were identified by PCR and/or serology. Patient characteristics, clinical symptoms, pneumonia severity and inflammation markers were assessed upon presentation. Duration of symptoms, prior therapy and length of hospital stay were retrieved from the hospital information system. Results: In all, 40 patients with acute Q fever pneumonia were identified. Of these, 29 were seronegative and 11 seropositive at presentation. C-reactive protein (CRP) was the only inflammation marker increased in all seronegative and seropositive patients but no significant difference was observed between groups. In seronegative patients, hypophosphatemia was more common (p=0.01), and length of hospital stay was longer (p=0.02). However, there was no significant difference in pneumonia severity index. Furthermore, phosphate levels were inversely correlated with body temperature (p=0.003). Conclusions: In acute Q fever pneumonia, CRP is the only traditional inflammation marker adequately reflecting disease activity. Patients with seronegative acute Q fever pneumonia present with hypophosphatemia and have prolonged length of hospital stay when compared to seropositive patients, suggesting an increased disease severity