Non-diagnostic anti-C. burnetii phase I IgG titres: Should they be discarded in elderly patients?

Abstract

Background: High anti-Coxiella burnetii phase I IgG titres are associated with chronic Q fever; an infectious disease with high mortality. Prognostic significance of lower or medium IgG phase I titres remain uncertain. The aim of this study was to explore this issue in a high-risk population. Methods: Sero-epidemiological and prospective study of 456 hospitalised patients aged 65 and older (Burgos; Spain). Serum IgG antibody phase I and II were determined by immunofluorescence assay. Results: A lower or medium IgG phase I titres (<1:1024) was observed in 180 (39.4%) patients. Atherosclerotic cardiovascular disease was associated with these titres, but not the traditional risk factors of chronic Q fever (cardiac valve disease, and vascular grafts or valvular prosthesis) (adjusted OR 1.75, 95% CI 1.18-2.61). Lower or medium IgG phase I titres were also associated with decreased survival at 30 months follow-up in patients with atherosclerotic cardiovascular disease (but not in the total sample) after adjusting for others comorbidities: IgG phase I titres ≥ 1:32 (HR 1.77; 95% CI 1.14 4–2.74), ≥1:64 (HR 1.90; 95% CI 1.21-2.99)–3.25), and ≥1:128 (HR 2.00; 95% CI 1.23–3.25). Conclusion: Lower or medium IgG phase I titres against C. burnetii, even the lowest, should not be discarded in elderly patients with atherosclerotic cardiovascular disease. Serological follow-up should be recommended in this group of patients. Keywords: Q fever, Serology, Coxiella burnetii, Atherosclerosis, Cardiovascular disease, Survival