Diagnostic value of serum pneumococcal DNA load during invasive pneumococcal infections.

Detection of pneumococcal DNA in blood could be a fast alternative for blood culture in invasive pneumococcal disease (IPD). In this study we compared the diagnostic value of the serum pneumococcal DNA load between different clinical syndromes in adults with bacteremic pneumococcal infections, also after initiation of antibiotic treatment. Adults hospitalized with a blood culture proven pneumococcal infection between December 2008 and June 2013 were retrospectively included. Pneumococcal DNA loads in corresponding serum samples were determined by qPCR. Data on clinical diagnosis, course of disease and antibiotic treatment were extracted from medical records. For 53 IPD cases eligible stored serum samples were retrieved. The proportion of samples positive in qPCR was lower in uncomplicated pneumonia compared with other clinical syndromes (59.5 % vs. 100 %, p = 0.005). The pneumococcal DNA load was higher in cases other than uncomplicated pneumonia (p = 0.043) as well as in more severe disease (p-values 0.018, 0.029 and 0.003 for PSI Risk Class IV/V, ICU admission and mortality, respectively). Both detection of pneumococcal DNA and distribution of load did not significantly change over the first days of hospitalization despite treatment with appropriate antibiotics. Detection of pneumococcal DNA in serum was more sensitive in clinical syndromes other than uncomplicated pneumonia. Furthermore, the pneumococcal DNA load was associated with the type of IPD and severity of disease. Since the serum pneumococcal DNA load seemed unaffected by antibiotic treatment during the first days of IPD, it may offer an alternative for culture methods after prior antibiotic use.