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Molecular diagnosis is valid for culture negative infective endocarditis

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Patients with suspected infective endocarditis can expect a more reliable diagnosis after a clinical validation study has confirmed that molecular methods are suitable for identifying the causal organisms in culture negative endocarditis.

A universal bacterial or fungal PCR test was positive in samples of heart valves from 14 of 15 patients with culture negative endocarditis who had undergone surgery; 11 patients had a positive bacterial and three a positive fungal test. Bacteria were identified in eight patients as species of Staphylococcus, Streptococcus, Enterobacter and—unusually—Tropheryma whipelii and Borrelia burgdorferi (sensu lato). Background contamination made the others unidentifiable. Fungi were identified as Aspergillus and Candida spp. Samples from 13 controls were PCR negative. These results correlated with clinical criteria except in two patients; their condition was asymptomatic and evident only at operation.

The retrospective case-control study included 15 culture negative patients with infective endocarditis according to Duke criteria—clinical measures of the condition—and 13 age and sex matched controls who needed valve replacement for other reasons. Samples were taken aseptically during the operation. These were subjected to universal bacterial and fungal PCR with primers from conserved sequences of rRNA genes. Amplified products were analysed by fragment length or restriction fragment length polymorphism, or were sequenced, as necessary. The results were compared with data from the case notes.

Culture negative infective endocarditis has a high death rate and complication rate. Identifying the culprit quickly and reliably means that correct treatment—with surgery if needed—can be started sooner.