Q fever endocarditis

Long-term persistence of Coxiella burnetii after acute primary Q fever

BACKGROUND

Long-term persistence of C. burnetii in infected animals was established in the 1950s and 60s, but the implications for human Q fever are not fully explored.

AIM

To compare the prevalence of markers of infection in a cohort of Q fever patients in Australia (up to 5 years after infection) with those in the 1989 Birmingham cohort (12 years after infection).

DESIGN

Case follow-up study.

METHODS

C. burnetii was tested for by: (i) antibodies to Phase 1 and 2 antigens in the three immunoglobulin classes; (ii) detection of DNA in bone marrow and peripheral blood mononuclear cells by PCR assays directed against several different targets in the genome; and (iii) attempts to isolate coxiellas in cell culture or mice from PCR-positive samples. Amplicon specificity was verified by fluorometric probing and by sequencing. Cross-contamination was excluded by extensive use of non-template controls, and in particular by the use of certain IS1111a target sequences.

RESULTS

Irrespective of clinical state, both groups remained seropositive, principally exhibiting medium levels of IgG antibody against C. burnetii Phase 2 antigen. C. burnetii genomic DNA was detected by PCR in 65% of bone marrow aspirates from Australian patients and approximately 88% of Birmingham patients. No coxiella were isolated from PCR positive samples.

DISCUSSION

We propose a provisional model for persistence. In Q fever without sequelae, the process is largely confined to the bone marrow. In Q fever fatigue syndrome (QFS), it is modulated by the patient's immunogenetic background to give higher levels of coxiella genomes in bone marrow and increased shedding into the peripheral blood. In Q fever endocarditis, late pregnancy, or during iatrogenic or other immunosuppression, the multiplication cycle is prolonged, and a potential source of live organisms.

A comparison of Q fever endocarditis with native valve endocarditis

We compared 10 episodes (8 patients) of Q fever endocarditis with 27 episodes (27 patients) of native valve endocarditis. Patients with Q fever endocarditis were more likely to have weight loss (p less than 0.003), experience fatigue (p less than 0.07), have clubbing of the fingers (p less than 0.005), have a diastolic murmur at the time of admission (p less than 0.03), be anemic (p less than 0.05), have a normal white blood cell count (p less than 0.005), and have a higher serum globulin concentration (p less than 0.007). While valve replacement was required for 50% of the episodes in both groups of patients, it was required later--mean 107 days following the onset of treatment--for the Q fever patients than for the native valve patients--mean 27 days. The mortality rates for these two diseases were not significantly different (30% for native endocarditis vs. 12.5% for Q fever endocarditis), but the Q fever patients experienced significantly fewer complications.