Definition of etiological agent

We determined that the detected microorganism was the causal etiology of CAP, with a high probability in the following cases: bacterial growth in blood culture or pleural fluid, S pneumoniae antigen in pleural fluid, positive PCR in blood, a fourfold increase in the IgG serology in serial samples, positive PCR in nasopharyngeal exudate for atypical bacteria, and positive PCR in nasopharyngeal exudate for RSV, hMPV, influenza A and B and PIV.