Time To Blood Culture Positivity Predicts Infective Endocarditis

By LabMedica International staff writers
Posted on 16 Aug 2018

Blood cultures are used to detect the presence of bacteria or fungi in the blood, to identify the type present, and to guide treatment. Testing is used to identify a blood infection (septicemia) that can lead to sepsis, a serious and life-threatening complication.

Time to blood culture positivity (TTP), a routinely available parameter in automated blood culture systems, may be a proxy for infectious burden in patients with bloodstream infections. The association between TTP and infective endocarditis (IE), or death, in patients with Staphylococcus aureus bacteremia has been studied.

Image: Mannitol salt agar plate with oxacillin showing methicillin-resistant Staphylococcus aureus (Photo courtesy of Medical College, Pondicherry).

French scientists collaborating with the Université Rennes-1 (Rennes, France) carried out a multicenter prospective cohort study that included all adult patients with S. aureus bacteremia in eight university hospitals in France (2009-2011). They analyzed data from four centers, which collected data on TTP. Regression models were used to study the association between TTP and definite IE (Duke-Li criteria), and 30-day mortality.

The investigators included 587 patients with S. aureus bacteremia: mean age was 65.3±16.3 years, 420/587 patients (71.6%) were male, 121/587 (20.6%) died, and 42/587 (7.2%) had definite IE. Median TTP of first positive blood culture was 13.7 hours (interquartile range, 9.9-18). On multivariate analysis, 30-day mortality was associated with TTP≤13.7 hours (74/295 (25.1%) versus 47/292 (16.1%), as well as old age, McCabe score, methicillin resistance, stroke, pneumonia, and C-Reactive Protein. TTP was also independently associated with IE, but with a U-shape curve: IE was more common in the first (TTP<10 hours, 17/148, 11.5%), and the last (TTP>18 hours, 8/146, 5.5%) quartiles of TTP.

The authors concluded that TTP provides reliable information in patients with S. aureus bacteremia, on the risk of IE, and prognosis, with short TTP being an independent predictor of death. This data readily available at no cost may be used to identify patients who require specific attention. The study was published on July 20, 2018, in the journal Clinical Microbiology and Infection.

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Université Rennes-1