Chronic Q fever: review of the literature and a proposal of new diagnostic criteria

A review was performed to determine clinical aspects and diagnostic tools for chronic Q fever. We present a Dutch guideline based on literature and clinical experience with chronic Q fever patients in The Netherlands so far. In this guideline diagnosis is categorized as proven, possible or probable chronic infection based on serology, PCR, clinical symptoms, risk factors and diagnostic imaging.     

Long-term serological follow-up after primary Coxiella burnetii infection in patients with vascular risk factors for chronic Q fever

We evaluated the long-term serological follow-up of patients with vascular risk factors for chronic Q fever that were previously Coxiella burnetii seropositive. C. burnetii phase I IgG titers were reevaluated in patients that gave informed consent or retrospectively collected in patients already deceased or lost to follow-up. Of 107 patients, 25 (23.4%) became seronegative, 77 (72.0%) retained a profile of past resolved Q fever infection, and five (4.7%) developed chronic Q fever. We urge clinicians to stay vigilant for chronic Q fever beyond two years after primary infection and perform serological testing based on clinical presentation.

     

Q fever in the Netherlands from 2007 to 2010

Since 2007, the Netherlands is faced with the largest outbreak of Q fever ever reported. In the last four years, over 4000 cases have been reported. The course of the epidemic and possible factors associated with this sudden surge in cases of Q fever is described and the preventive measures in the veterinary sector and the outbreak management of this unique epidemic are summarised. Finally, the latest data on clinical presentation and diagnostic and therapeutic dilemmas of Q fever in the Netherlands are reviewed.     

The value of 18F-FDG PET/CT in diagnosing infectious endocarditis

Purpose

Early detection of infectious endocarditis is challenging. For diagnosing infectious endocarditis, the revised Duke criteria are the gold standard. Evidence of endocardial involvement on echocardiography is a major criterion, but sensitivity and specificity of echocardiography are not optimal. Here we investigated the utility of ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography and computed tomography (PET/CT) to diagnose infectious endocarditis in patients with gram-positive bacteraemia.

Methods

Seventy-two patients with gram-positive bacteraemia were prospectively included. Patients with a positive blood culture growing Staphylococcus aureus, Streptococcus species or Enterococcus species were eligible when a risk factor for developing metastatic infectious foci was present. Infectious endocarditis was defined according to the revised Duke criteria. All patients underwent ¹⁸F-FDG PET/CT and echocardiography. ¹⁸F-FDG uptake in or around the heart valves was evaluated independently by two nuclear medicine physicians.

Results

Sensitivity for diagnosing infectious endocarditis with ¹⁸F-FDG PET/CT was 39 % and specificity was 93 %. The positive predictive value was 64 % and negative predictive value was 82 %. The mortality rate in patients without infectious endocarditis and without increased ¹⁸F-FDG uptake in or around the heart valves was 18 %, and in patients without infectious endocarditis but with high ¹⁸F-FDG uptake in or around the heart valves the mortality rate was 50 % (p?=?0.181).

Conclusion

¹⁸F-FDG PET/CT is currently not sufficiently adequate for the diagnosis of infectious endocarditis because of its low sensitivity. Improvements such as patient preparation with low carbohydrate–fat allowed diet and technical advances in the newest PET/CT scanners may increase sensitivity in future studies.     

Microbiological Challenges in the Diagnosis of Chronic Q Fever

Diagnosis of chronic Q fever is difficult. PCR and culture lack sensitivity; hence, diagnosis relies mainly on serologic tests using an immunofluorescence assay (IFA). Optimal phase I IgG cutoff titers are debated but are estimated to be between 1:800 and 1:1,600. In patients with proven, probable, or possible chronic Q fever, we studied phase I IgG antibody titers at the time of positive blood PCR, at diagnosis, and at peak levels during chronic Q fever. We evaluated 200 patients, of whom 93 (46.5%) had proven, 51 (25.5%) had probable, and 56 (28.0%) had possible chronic Q fever. Sixty-five percent of proven cases had positive Coxiella burnetii PCR results for blood, which was associated with high phase I IgG. Median phase I IgG titers at diagnosis and peak titers in patients with proven chronic Q fever were significantly higher than those for patients with probable and possible chronic Q fever. The positive predictive values for proven chronic Q fever, compared to possible chronic Q fever, at titers 1:1,024, 1:2,048, 1:4,096, and ≥1:8,192 were 62.2%, 66.7%, 76.5%, and ≥86.2%, respectively. However, sensitivity dropped to <60% when cutoff titers of ≥1:8,192 were used. Although our study demonstrated a strong association between high phase I IgG titers and proven chronic Q fever, increasing the current diagnostic phase I IgG cutoff to >1:1,024 is not recommended due to increased false-negative findings (sensitivity < 60%) and the high morbidity and mortality of untreated chronic Q fever. Our study emphasizes that serologic results are not diagnostic on their own but should always be interpreted in combination with clinical parameters.