Diagnosis of invasive pneumococcal infection by PCR amplification of Streptococcus pneumoniae genomic fragments in blood: a multi-centre comparative study.

The increasing interest in the prevention of pneumococcal disease by immunisation necessitates improved organism-specific surveillance. This is particularly the case with regard to the contribution of Streptococcus pneumoniae infection to community-acquired pneumonia where blood cultures are often negative and sputum culture results ambiguous. Examination by PCR of blood samples taken at hospital admission offers one possibility for such improvement. The sensitivity, specificity and convenience of three pneumolysin gene PCR assays were compared in a large study, using EDTA blood from 175 patients (95 with proven pneumococcal bacteraemia, 80 with bacteraemia due to other organisms). The assays used were a PCR-enzyme immunoassay, a hybridisation probe assay run on the Roche LightCycler and a hydrolysis probe (TaqMan) assay run on an ABI 7700. Overall samples from only 57% of patients with bacteraemic pneumococcal infection yielded a positive result in at least one assay. Individual sensitivities ranged from 45% (TaqMan/ABI) through 35% (PCR-EIA) to 21% (Hybridisation/LightCycler). Specificity (PCR negative in the 80 control patients) ranged from 97-100%. The TaqMan/ABI assay was run in two centres and concordance between results was 91.4%, discrepancies being associated with very weakly positive samples. Overall, the TaqMan/ABI was the most sensitive and convenient assay; however, this method does not appear to offer any significant improvement over conventional blood cultures and is unlikely to be sufficiently sensitive to confirm a pneumococcal aetiology for non-bacteraemic pneumococcal pneumonia. For the present, therefore, blood culture is the preferred option.