Molecular and serological techniques for the diagnosis of culture negative infective endocarditis in Alexandria Main University Hospital

Background and aim: Culture-negative infective endocarditis (CNIE) is a diagnostic dilemma. The study was carried out to estimate the prevalence of CNIE among definite IE cases, to describe the epidemiologic and clinical characteristics of CNIE patients and to diagnose the microbial etiology of CNIE using molecular and serological techniques. Subjects and methods: Sixty-five definite IE cases were enrolled in a prospective observational study between January and December 2010. CNIE cases were tested by 16SrRNA and seminested PCR for 35 blood samples, serological tests and the study of ten valve tissue specimens. Results: CNIE constituted 39 (60%) cases. The mean age of CNIE patients was 31 years. Male to female ratio was 2.9:1. Healthcare associated IE accounted for 15.4%, native valve IE for 66.7% and intravenous drug abuse for 20.5% of cases. The mitral valve was the most frequently involved (56.4%). Out of 39 CNIE cases, seminested blood PCR detected 12 cases (ten Staphylococci, two Streptococci). Five cases were reactive by serology (three Bartonella, one Coxiella, and one Brucella). Six cases were positive by analysis of valve tissue (three Staphylococci, three Streptococci). The combined results of all diagnostic tools decreased the percentage of non-identified causes of CNIE from 60% to 24.6%. Conclusions: Our data underlined the role of collecting blood culture before starting antibiotics and the role of seminested PCR in the diagnosis of conventional causes of CNIE. The importance of serology to identify non conventional causes was also highlighted