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Molecular method simplifies diagnosis of infective endocarditis

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Microbiologists in the UK are enthusiastic about the role of 16S rRNA sequencing in helping to identify endocarditis, after using it to diagnose a case of culture negative infective endocarditis.

Theirs was a classic case after previous recent antibiotic treatment, which sequencing confirmed as streptococcal endocarditis, but the method is as valuable for diagnosing endocarditis caused by fastidious bacteria, hazardous species, and rare pathogens.

The case was in a 62 year old previously fit man admitted after a month of vomiting, weight loss, and low grade fever, initially given antibiotics for suspected upper respiratory tract infection. However, tests disclosed acute renal failure with immune complex glomerulonephritis, and a transthoracic echocardiogram three days later showed a mobile mass on the right coronary cusp of the aortic valve. Empirical treatment for endocarditis based on probable streptococcal infection was started after three sets of blood cultures failed to grow pathogens.

After initial improvement fever returned on day 13, with a vasculitic rash on his legs and splinter haemorrhages on his metatarsals. Repeat echocardiography showed thickening of the entire left and right coronary cusps and severe aortic regurgitation, which led to valve replacement. The appearance was typical of subacute bacterial endocarditis histologically, with masses of Gram positive cocci. Cultures of the valve produced no growth, but 16S rRNA sequencing identified Streptococcus sanguis.

Traditional methods of diagnosis rely on culturing or serological testing for likely bacterial pathogens. But 10–15% of cases of infective endocarditis in the UK are culture negative, mostly because of previous antibiotic treatment.

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