Fluorescence in situ hybridization for detecting Coxiella burnetii in tissue samples from chronic Q fever patients.

OBJECTIVE: Detection of the intracellular bacterium Coxiella burnetii, causative agent of chronic Q fever, is notoriously difficult. Diagnosis of and duration of antibiotic treatment for chronic Q fever is partly determined by detection of the bacterium with polymerase chain reaction (PCR). Fluorescence in situ hybridization (FISH) might be a promising technique for detecting C. burnetii in tissue samples from chronic Q fever patients, but its value in comparison with PCR is uncertain. We aim to assess the value of FISH for detecting C. burnetii in tissue of chronic Q fever patients. METHODS: FISH and PCR were performed on tissue samples from Dutch chronic Q fever patients collected during surgery or autopsy. Sensitivity, specificity, and overall diagnostic accuracy were calculated. Additionally, data on patient and disease characteristics were collected from electronic medical records. RESULTS: In total, 49 tissue samples from mainly vascular walls, heart valves, or placentas, obtained from 39 chronic Q fever patients, were examined by FISH and PCR. The sensitivity and specificity of FISH compared to PCR for detecting C. burnetii in tissue samples from chronic Q fever patients was 45.2% (95% confidence interval (CI), 27.3% - 64.0%) and 84.6% (95% CI, 54.6% - 98.1%), respectively. The overall diagnostic accuracy was 56.8% (95% CI, 42.2% - 72.3%). Two C. burnetii PCR negative placentas were FISH positive. Four FISH results (8.2%) were deemed inconclusive because of autofluorescence. CONCLUSION: With an overall diagnostic accuracy of 57.8%, we conclude that FISH has limited value in the routine diagnostics of chronic Q fever.

Still New Chronic Q Fever Cases Diagnosed 8 Years After a Large Q Fever Outbreak.

BACKGROUND: Chronic Q fever usually develops within 2 years after primary infection with Coxiella burnetii. We determined the interval between acute Q fever and diagnosis of chronic infection, assessed what factors contribute to a longer interval, and evaluated the long-term follow-up. METHODS: From 2007 to 2018, patients with chronic Q fever were included from 45 participating hospitals. The interval between acute and chronic infection was calculated in patients with a known day of first symptoms and/or serological confirmation of acute Q fever. Chronic Q fever-related complications and mortality were assessed by 2 investigators based on predefined criteria. RESULTS: In total, 313 (60.3%) proven, 81 (15.6%) probable, and 125 (24.1%) possible chronic Q fever patients were identified. The date of acute Q fever was known in 200 patients: in 45 (22.5%), the interval was longer than 2 years, with the longest observed interval being 9.2 years. Patients in whom serological follow-up was performed after acute Q fever were diagnosed less often after this 2-year interval (odds ratio, 0.26; 95% confidence interval, 0.12-0.54). Chronic Q fever-related complications occurred in 216 patients (41.6%). Chronic Q fever-related mortality occurred in 83 (26.5%) of proven and 3 (3.7%) of probable chronic Q fever patients. CONCLUSIONS: Chronic Q fever is still being diagnosed and mortality keeps occurring 8 years after a large outbreak. Intervals between acute Q fever and diagnosis of chronic infection can reach more than 9 years. We urge physicians to perform microbiological testing for chronic Q fever even many years after an outbreak or acute Q fever disease.

The prognostic value of serological titres for clinical outcomes during treatment and follow-up of patients with chronic Q fever.

OBJECTIVES: We assessed the prognostic value of phase I IgG titres during treatment and follow-up of chronic Q fever. METHODS: We performed a retrospective cohort study to analyse the course of phase I IgG titres in chronic Q fever. We used a multivariable time-varying Cox regression to assess our primary (first disease-related event) and secondary (therapy failure) outcomes. In a second analysis, we evaluated serological characteristics after 1 year of therapy (fourfold decrease in phase I IgG titre, absence of phase II IgM and reaching phase I IgG titre of ≤1:1024) with multivariable Cox regression. RESULTS: In total, 337 patients that were treated for proven (n = 284, 84.3%) or probable (n = 53, 15.7%) chronic Q fever were included. Complications occurred in 190 (56.4%), disease-related mortality in 71 (21.1%) and therapy failure in 142 (42.1%) patients. The course of phase I IgG titres was not associated with first disease-related event (HR 1.00, 95% CI 0.86-1.15) or therapy failure (HR 1.02, 95% CI 0.91-1.15). Similar results were found for the serological characteristics for the primary (HR 0.97, 95% CI 0.62-1.51; HR 1.12, 95% CI 0.66-1.90; HR 0.99, 95% CI 0.57-1.69, respectively) and secondary outcomes (HR 0.86, 95% CI 0.57-1.29; HR 1.37, 95% CI 0.86-2.18; HR 0.80, 95% CI 0.48-1.34, respectively). DISCUSSION: Coxiella burnetii serology does not reliably predict disease-related events or therapy failure during treatment and follow-up of chronic Q fever. Alternative markers for disease management are needed, but, for now, management should be based on clinical factors, PCR results, and imaging results.

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.

Pitfalls of molecular diagnostic testing for Coxiella burnetii DNA on throat swabs.

INTRODUCTION: Coxiella burnetii, the causative pathogen of Q fever, is regularly detected in throat swabs from patients without serological evidence of Q fever infection. C. burnetii is also frequently found in bulk tank milk from dairy cows. We evaluated the false positivity rate of polymerase chain reaction (PCR) for C. burnetii DNA on throat swabs and investigated whether recent consumption of C. burnetii DNA-positive cow milk could contribute to this phenomenon. METHODS: C. burnetii PCR was performed on throat swabs obtained from patients in whom a throat swab was ordered for other diagnostic purposes; patients with community-acquired pneumonia (CAP); and healthy volunteers after consumption of commercial C. burnetii-containing cow milk products. RESULTS: C. burnetii DNA was found in 5.0% of throat swabs ordered for other diagnostic purposes and in 15.3% of throat swabs from CAP patients without serological evidence of Q fever pneumonia. The positive and negative predictive value of C. burnetii PCR on throat swabs for Q fever pneumonia were 66.7% (95% CI, 38.0-88.2) and 48.9% (95% CI, 41.3-54.6), respectively. After consumption of commercial C. burnetii-containing cow milk products, C. burnetii DNA could be detected in throat swabs for as long as 30 min after ingestion. CONCLUSION: C. burnetii PCR on throat swabs is of low diagnostic value for Q fever pneumonia and was false positive in 15.3% of CAP patients without Q fever pneumonia. Recent consumption of C. burnetii-containing products can influence the outcome of C. burnetii PCR on throat swabs. Therefore, diagnosis of C. burnetii infection should be made in combination with serology or PCR performed on blood.