Practical and theoretical aspects of postmortem bacteriology

A positive blood culture or culture of cerebrospinal fluid (CSF) obtained postmortem could be due to a genuine positive, to agonal spread, to postmortem translocation or to contamination. A review of published evidence indicates that, if specimens are taken with care, the majority is sterile. Mixed growth occurs in less than 10% and is mainly due to contamination. Postmortem translocation is rarely a problem if the body is refrigerated promptly after death. Agonal change is less common than often assumed. A single isolate of a potential pathogen in perinatal cases and in adult practice is likely to be a genuine positive (PPV>50%); in sudden unexpected death in infancy (SUDI), however, a single isolate should be regarded as only a possible cause of death (PPV<50%) in the absence of corroboration. If bacterial invasion causes or contributes to rapid death, there might not be time for the histological changes of inflammation to develop and more subtle signs should be sought; including cell counts and protein estimations of CSF. Sampling upper-airways secretions shortly after death and before refrigeration provides useful information if infection is suspected. The results can be compared with community controls in epidemiological studies. In the future, genomic and proteomic techniques need to be added to standard methods to determine the role of bacteria in sudden death. The key message is that if specimens are taken with care, and interpreted with care, then useful information can be obtained.