Les diatomées. Utilité de la recherche et limites de la méthode. Enquête auprès des instituts médicolégaux et des laboratoires. Bilan de trois années d'expertise à l'IRCGN (2014-2016)

Diatoms are a reliable diagnostic tool for drowning. Yet, they are at the origin of controversies due to limits linked to the discovery site, discrepancies in the results induced by the methods used or non-conformities affecting the expression of the results. A survey of 26 forensic institutes (metropolitan France and DROM/COM) and 10 French laboratories was undertaken to get state of the art about drowning diagnostic techniques used from a sample of freshwater human corpses discovered in 2010 and 2011. The analysis highlights biases and limitations mainly related to methodological sampling rules, rate of decomposition of the corpse likely to cause hypothetic post mortem contamination of organs. Comparison of medico-legal data and laboratories results focus on representativeness of autopsy samples. In 2014, a “diatom” sampling kit was developed in the department 3F of the IRCGN. Single-use materials allow standardization of a sampling method at the discovery field and during autopsy. Between 2014 and 2016, the balance of diatoms activity at the IRCGN highlights an increase of analyses and a significant reduction of expertise delays. If the problem of water sampling is being resolved with the use of the kit, the main source of nonconformity always concerns the autopsy sample mass. A lower mass than normally required by the protocol is able to induce the rejection of analysis results. Standardization of a sampling method seems to be an effective solution to the problem of samples non-conformity. Furthermore, study of the “statistical weight” of an organ and blood diffusion phenomena will allow diatoms to give new light in case of suspicion of underlying pathology or sampling problem.