Conventional viral cultures and shell vial assay for diagnosis of apparently culture-negative Coxiella burnetii endocarditis

Genome sequence of Coxiella burnetii strain Namibia

We present the whole genome sequence and annotation of the Coxiella burnetii strain Namibia. This strain was isolated from an aborting goat in 1991 in Windhoek, Namibia. The plasmid type QpRS was confirmed in our work. Further genomic typing placed the strain into a unique genomic group. The genome sequence is 2,101,438 bp long and contains 1,979 protein-coding and 51 RNA genes, including one rRNA operon. To overcome the poor yield from cell culture systems, an additional DNA enrichment with whole genome amplification (WGA) methods was applied. We describe a bioinformatics pipeline for improved genome assembly including several filters with a special focus on WGA characteristics.

Q fever endocarditis: an unusual presentation

Coxiella burnetii, the agent of Q fever, is an obligate intracellular pathogen typically associated with exposure to livestock. This organism may present with acute or chronic manifestations, the most typical chronic manifestation being endocarditis. We report a highly unusual case of Q fever endocarditis acquired in the United States marked by atypical cardiac manifestations.

Long-term outcome of Q fever endocarditis: a 26-year personal survey

BACKGROUND

Q fever endocarditis caused by Coxiella burnetii is a potentially fatal disease characterised by a chronic evolution. To assess the long-term outcome and identify prognostic factors for mortality, surgical treatment, and serological changes in Q fever endocarditis, we did a retrospective study in the French National Referral Centre.

METHODS

Patients included were diagnosed with Q fever endocarditis at our centre from May, 1983, to June, 2006, and followed up for a minimum of 3 years for each patient, history and clinical characteristics were recorded with a standardised questionnaire. Prognostic factors associated with death, surgery, serological cure, and serological relapse were assessed by Cox regression analysis. Excised heart valve analysis was assessed according to duration of treatment.

FINDINGS

104 patients were identified for inclusion in the study, although one was lost to follow-up; median follow-up was 100 months (range 37-310 months). 18 months of treatment was sufficient to sterilise the valves of all the patients except three, and 2 years of treatment sterilised all valves except one. In a multivariate Cox regression analysis, the major determinants associated with mortality were age (hazard ratio 1.11, 95% CI 1.05-1.18, p=0.003), stroke at diagnosis (7.09, 2.00-25.10, p=0.001), endocarditis on a prosthetic valve (6.04, 1.47-24.80, p=0.044), an absence of a four-times decrease of phase I IgG and IgA at 1 year (5.69, 1.00-32.22, p=0.049), or the presence of phase II IgM at 1 year (12.08, 3.11-46.85, p=0.005). Surgery was associated with heart failure (2.68, 1.21-5.94, p=0.015) or a cardiac abscess (4.71, 1.64-13.50, p=0.004). The determinants of poor serological outcome were male sex (0.47, 0.26-0.86, p=0.014), a high level of phase I IgG (0.65, 0.45-0.95, p=0.027), and a delay in the start of treatment with hydroxychloroquine (0.20, 0.04-0.91, p=0.037). Factors associated with relapse were endocarditis on a prosthetic valve (21.3, 2.05-221.86, p=0.01) or treatment duration less than 18 months (9.69, 1.08-86.72, p=0.042).

INTERPRETATION

The optimum duration of treatment with doxycycline and hydroxychloroquine in Q fever endocarditis is 18 months for native valves and 24 months for prosthetic valves. This duration should be extended only in the absence of favourable serological outcomes. Patients should be serologically monitored for at least 5 years because of the risk of relapse.

FUNDING

French National Referral Centre for Q Fever.

Current laboratory diagnosis of Q fever

Q fever is a worldwide zoonosis caused by the strictly intracellular bacterium Coxiella burnetii. Among symptomatic patients (one-half of patients remain asymptomatic), acute Q fever most frequently manifests as a self-limited febrile illness, pneumonia, or hepatitis. Endocarditis is the predominant form of chronic Q fever. All the classical techniques of bacteriology may be used for diagnosis of C burnetii infection. Nonetheless, because of the risk of contamination, isolation must be performed in biosafety level 3 laboratories. Moreover, to date no diagnostic tests for detection by polymerase chain reaction or specific antibodies for immunochemistry are available commercially. Hence, Q fever is diagnosed in most cases by serology. The most reliable technique appears to be micro-immunofluorescence, which exhibits both good sensitivity and specificity. A wider use of this serology in cases of blood culture-negative endocarditis, atypical pneumonia, unexplained fever, and hepatitis should lead to an increase of diagnosed cases.

Q fever

Q fever is a zoonosis with a worldwide distribution with the exception of New Zealand. The disease is caused by Coxiella burnetii, a strictly intracellular, gram-negative bacterium. Many species of mammals, birds, and ticks are reservoirs of C. burnetii in nature. C. burnetii infection is most often latent in animals, with persistent shedding of bacteria into the environment. However, in females intermittent high-level shedding occurs at the time of parturition, with millions of bacteria being released per gram of placenta. Humans are usually infected by contaminated aerosols from domestic animals, particularly after contact with parturient females and their birth products. Although often asymptomatic, Q fever may manifest in humans as an acute disease (mainly as a self-limited febrile illness, pneumonia, or hepatitis) or as a chronic disease (mainly endocarditis), especially in patients with previous valvulopathy and to a lesser extent in immunocompromised hosts and in pregnant women. Specific diagnosis of Q fever remains based upon serology. Immunoglobulin M (IgM) and IgG antiphase II antibodies are detected 2 to 3 weeks after infection with C. burnetii, whereas the presence of IgG antiphase I C. burnetii antibodies at titers of >/=1:800 by microimmunofluorescence is indicative of chronic Q fever. The tetracyclines are still considered the mainstay of antibiotic therapy of acute Q fever, whereas antibiotic combinations administered over prolonged periods are necessary to prevent relapses in Q fever endocarditis patients. Although the protective role of Q fever vaccination with whole-cell extracts has been established, the population which should be primarily vaccinated remains to be clearly identified. Vaccination should probably be considered in the population at high risk for Q fever endocarditis.

Infective endocarditis due to unusual or fastidious microorganisms

Infective endocarditis due to fastidious microorganisms is commonly encountered in clinical practice. Some organisms such as fungi account for up to 15% of cases of prosthetic valve infective endocarditis, whereas organisms of the HACEK group (Haemophilus parainfluenzae, H. aphrophilus, and H. paraphrophilus, Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, and Kingella kingae) cause 3% of community-acquired cases of infective endocarditis. Special techniques are necessary to identify these microorganisms. A history of contact with mammals or birds may suggest infection caused by Coxiella burnetii (Q fever), Brucella species, or Chlamydia psittaci. A nosocomial cluster of postsurgical infective endocarditis may be caused by Legionella species or Mycobacterium species. If risk factors that are commonly associated with fungal infections (cardiac surgical treatment, prolonged hospitalization, indwelling central venous catheters, and long-term antibiotic use) are present, fungal endocarditis is possible. Patients with endocarditis and a history of periodontal disease or dental work in whom routine blood cultures are negative might have infection due to nutritionally variant streptococci or bacteria of the HACEK group. Communication between the microbiologist and the clinician is of crucial importance for identification of these microorganisms early during the course of the infection before complications such as embolization or valvular failure occur. In this article, we review the microbiologic and clinical features of these organisms and provide recommendations for diagnosis and treatment.