英国和爱尔兰每年大约发生 2500 例脑炎。[3]Encephalitis Society. Questions and answers. 2008. http://www.encephalitis.info/ (last accessed 3 August 2017).http://www.encephalitis.info/images/iPdf/Resources/FactSheets/fs001QuestionsAnswers.pdf美国每年大约有 20,000 例。[4]Vora NM, Holman RC, Mehal JM, et al. Burden of encephalitis-associated hospitalizations in the United States, 1998-2010. Neurology. 2014;82:443-451.http://www.ncbi.nlm.nih.gov/pubmed/24384647?tool=bestpractice.com发病率约为十万分之七。这个发病率比法国、意大利、加拿大和澳大利亚出院数据中报告的发病率高。[5]Granerod J, Ambrose HE, Davies NW, et al. Causes of encephalitis and differences in their clinical presentations in England: a multicentre, population-based prospective study. Lancet Infect Dis. 2010;10:835-844.http://www.thelancet.com/journals/laninf/article/PIIS1473-3099(10)70222-X/fulltexthttp://www.ncbi.nlm.nih.gov/pubmed/20952256?tool=bestpractice.com[6]George BP, Schneider EB, Venkatesan A. Encephalitis hospitalization rates and inpatient mortality in the United States, 2000-2010. PloS One. 2014;9:e104169.http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0104169http://www.ncbi.nlm.nih.gov/pubmed/25192177?tool=bestpractice.com[7]Barbadoro P, Marigliano A, Ricciardi A, et al. Trend of hospital utilization for encephalitis. Epidemiol Infect. 2012;140:753-764.http://www.ncbi.nlm.nih.gov/pubmed/21733247?tool=bestpractice.com[8]Bernard S, Mailles A, Stahl JP, et al. Epidemiology of infectious encephalitis, differences between a prospective study and hospital discharge data. Epidemiol Infect. 2013;141:2256-2268.http://www.ncbi.nlm.nih.gov/pubmed/23168268?tool=bestpractice.com[9]Huppatz C, Durrheim DN, Levi C, et al. Etiology of encephalitis in Australia, 1990-2007. Emerg Infect Dis. 2009;15:1359-1365.https://wwwnc.cdc.gov/eid/article/15/9/08-1540_articlehttp://www.ncbi.nlm.nih.gov/pubmed/19788802?tool=bestpractice.com[10]Kulkarni MA, Lecocq AC, Artsob H, et al. Epidemiology and aetiology of encephalitis in Canada, 1994-2008: a case for undiagnosed arboviral agents? Epidemiol Infect. 2013;141:2243-2255.http://www.ncbi.nlm.nih.gov/pubmed/23148910?tool=bestpractice.com由于临床表现广泛,诊断率和报告率都低于实际患者数量,很难确定真正的发病率。没有明显的性别差异,但各年龄组的发病通常呈双峰分布:1 岁以下和 65 岁以上。
在美国和世界其他地区,某些病毒性脑炎病历有季节性(夏季和初秋多见肠道病毒和多数虫媒病毒)和地理(某些虫媒病毒)差异。
自 20 世纪 90 年代末起,与艾滋病病毒 (HIV) 感染有关的脑炎有所下降,现在逐步稳定。[4]Vora NM, Holman RC, Mehal JM, et al. Burden of encephalitis-associated hospitalizations in the United States, 1998-2010. Neurology. 2014;82:443-451.http://www.ncbi.nlm.nih.gov/pubmed/24384647?tool=bestpractice.com与此相反,与移植或免疫介导性疾病(免疫功能受损状态诱发的)有关的脑炎有所增加。