Association between pneumococcal load and disease severity in adults with pneumonia

Determination of pneumococcal load by quantitative PCR may be useful for diagnostic and prognostic purposes. We hypothesized that higher pneumococcal load would be associated with increased pneumonia severity. Therefore, we tested serum, sputum and urine specimens from 304 adults with community-acquired pneumonia by using a quantitative lytA pneumococcal real-time PCR assay. The association between pneumococcal load and disease severity was assessed using several markers of severity: CURBage score, PSI risk class, intensive care unit admission, in-hospital death and admission duration. For PCR-positive specimens, the bacterial loads were higher in sputum specimens [median 8.55×10(5) copies ml(-1); interquartile range (IQR) 4.70×10(4)-4.69×10(6) copies ml(-1)] than either serum (median 180 copies ml(-1); IQR 165-8970 copies ml(-1)) or urine (median 623 copies ml(-1); IQR 510-650 copies ml(-1)). Detection of pneumococcal DNA in serum was associated with severe disease, and there was evidence of a dose-response effect with increased bacterial load being associated with increased severity. The same observations were not observed for other specimen types. This study adds to an increasing body of evidence suggesting that determination of pneumococcal load has a clinical utility. Further work is needed to determine whether measuring pneumococcal load in respiratory specimens from adults will differentiate colonization from coincidental carriage.