Changing profile of encephalitis: Results of a 4-year study in France

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 Chi² 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.