Post-mortem interval and bacteriological culture yield in sudden unexpected death in infancy (SUDI)

It has been hypothesised that post-mortem translocation, the migration of micro-organisms from mucosal surfaces into the body after death, leads to microbial overgrowth in post-mortem samples, which is more frequently polymicrobial and which would be detected more frequently with increased post-mortem interval (PMI) from death to autopsy. This study aimed to evaluate the association between PMI and bacteriological yield in post-mortem examinations of sudden unexpected deaths in infancy (SUDI). A retrospective review of all microbiological findings from >500 SUDI autopsies (7-365 days of age) was performed as part of a larger review of >1500 paediatric autopsies over a 10-year period, 1996-2005. All autopsies were carried out in a single specialist centre by a small number of paediatric pathologists. For the 507 SUDI included in the analysis, there were 2079 samples collected for bacteriological culture. The median PMI was 2 days. The proportion of positive cultures decreased from 83% for samples taken within 24h of death, to 67% when taken five or more days after death (chi-square for linear trend=19.99, P<0.0001). Polymicrobial cultures decreased from 61% to 46% (chi-square for linear trend=12.88, P=0.0003), and cultures taken two or more days after death yielded significantly fewer isolates per sample than cultures taken less than 2 days after death (Mann-Whitney U-test, P=0.009). The findings of this study demonstrate that a PMI of several days' duration is neither associated with an increased frequency of positive cultures nor with an increased frequency of mixed-growth episodes as was hypothesised to occur with post-mortem translocation. Indeed, the opposite trend is observed, suggesting that a longer PMI may result in death of micro-organisms. However, these data do not allow assessment of the possibility of significant post-mortem translocation occurring within the first few hours after death. Whilst the interpretation of positive microbiological cultures in SUDI post-mortems remains difficult, a PMI of several days' duration is not associated with an increased risk of post-mortem translocation and routine microbiological sampling is recommended in all SUDI autopsies, even when there is a PMI of several days.