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International audience; CONTEXT: In 2007, we performed a nationwide prospective study to assess the epidemiology of encephalitis in France. We aimed to evaluate epidemiological changes 10years later. METHODS: We performed a 4-year prospective cohort study in France (ENCEIF) from 2016 to 2019. Medical history, comorbidities, as well as clinical, biological, imaging, and demographic data were collected. For the comparison analysis, we selected similar data from adult patients enrolled in the 2007 study. We used Stata statistical software, version 15 (Stata Corp). Indicative variable distributions were compared using Pearson’s Chi(2) test, and means were compared using Student’s t-test for continuous variables. RESULTS: We analyzed 494 cases from 62 hospitals. A causative agent was identified in 65.7% of cases. Viruses represented 81.8% of causative agents, Herpesviridae being the most frequent (63.6%). Arboviruses accounted for 10.8%. Bacteria and parasites were responsible for respectively 14.8% and 1.2% of documented cases. Zoonotic infections represented 21% of cases. When comparing ENCEIF with the 2007 cohort (222 adults patients from 59 hospitals), a higher proportion of etiologies were obtained in 2016-2019 (66% vs. 53%). Between 2007 and 2016-2019, the proportions of Herpes simplex virus and Listeria encephalitis cases remained similar, but the proportion of tuberculosis cases decreased (P=0.0001), while tick-borne encephalitis virus (P=0.01) and VZV cases (P=0.03) increased. In the 2016-2019 study, 32 causative agents were identified, whereas only 17 were identified in the 2007 study. CONCLUSION: Our results emphasize the need to regularly perform such studies to monitor the evolution of infectious encephalitis and to adapt guidelines.

Background Encephalitis and meningoencephalitis are severe, sometime life-threatening infections of the central nervous system. Travellers may be exposed to a variety of neurotropic pathogens. Aims We propose to review known infectious causes of encephalitis in adults acquired outside Europe, and how to identify them. Sources We used Pubmed and Embase, to search the most relevant publications over the last years. Content Microbiologic tests and radiological tools to best identify the causative pathogen in travellers presenting with encephalitis and ME are presented in this narrative review, as well as a diagnostic approach tailored to the visited area and types of exposures. Implications This review highlights the diagnostic difficulties inherent to exotic causes of central nervous system infections, and attempts to guide clinicians with respect to which microbiological tests to consider, in addition to brain MRI, when approaching a returning traveller presenting with encephalitis.

Background Encephalitis and meningoencephalitis imply inflammation of the brain parenchyma, and comprise many diagnostic entities, such as various infections and causes of dysimmunity. The cause remains unknown in around 50% of cases. Objectives To summarize the main infectious causes of encephalitis and meningoencephalitis acquired in Europe, and the diagnostic means to identify them. Sources PubMed, ECDC and WHO websites, personal experience. Content The principal infectious causes of encephalitis and meningoencephalitis acquired in Europe in adults are discussed in this review, with special emphasis on the microbiological and imaging diagnostic approaches. The role of electroencephalography in diagnosing encephalitis is also mentioned. Among infections, viruses are more frequent than other pathogen types, and their epidemiology varies according to geographic area. A few bacteria, such as Listeria monocytogenes and Mycobacterium tuberculosis, are also to be considered. In contrast, parasites and fungi are rare encephalitis causes in Europe. Implications Identifying the causative pathogen of infectious encephalitis and meningoencephalitis is complex because of the variety of pathogens, the epidemiology of which is determined by geography and environmental factors. Furthermore, despite extensive microbiological testing, many cases of encephalitis remain of unknown origin. Brain magnetic resonance imaging and electroencephalography are useful complementary diagnostic tools, and newer unbiased sequencing technologies might help to fill in the diagnostic gap.