HSV CNS infection 1. HSV DNA detected in CSF or an HSV-speciﬁc intrathecal antibody response, or 2. Evidence of primary HSV infection, that is, seroconversion to IgG or IgM, within 2 weeks of onset of serious neurologi- cal disease. Ethics approval Ethics approval was given by the Public Health Laboratory Service Ethics Committee, London. RESULTS Cases of serious neurological disease Of the 267 episodes of disease reported, 19 cases of HSV CNS infection (table 1) and 163 cases of serious neurological dis- ease were identiﬁed; 52 of the latter were in children aged 2–11 months and 111 in children aged 12–35 months. The clinical features, neuroimaging results and long-term outcome of the 19 cases are given in table 2. Every case pre- sented with convulsions (partial in 12/19) accompanied by fever in all but one instance. Focal neuroimaging abnormali- ties were noted in all children aged <11 months (temporal lobes in nine, frontal lobes in three and parietal lobes in seven) but in only one of the older children. There were no deaths, but 11 of the 13 children aged 2–11 months and three of the six older children had long-term neurological sequelae. The most common sequela was developmental delay, but other persist- ing deﬁcits included hemiparesis, quadriparesis and visual problems. Eight children had epilepsy. Two patients (nos. 12 and 15) with HSV CNS infection did not meet our case deﬁnition of serious neurological disease. Short report The remaining 17 (11 encephalitis, six severe illness with fever and convulsions) accounted for 23% (12/52) of episodes of serious neurological disease in children <1 year old and 4.5% (5/111) in the older children. Because all 17 cases were in British children, we could estimate the incidence of serious neurological disease due to HSV CNS infection in the UK as 1 in 64 000/year in children aged 2–11 months and 1 in 230 000/ year in children aged 12–35 months. In 1998–2001 there were 2.1 million children in the ﬁrst year of life and 4.1 million in the second and third years (National Statistics Ofﬁce website: http://www.statistics.gov.uk/popest). DISCUSSION This paper reports data on the incidence, spectrum of clinical presentation and long-term outcome of virologically conﬁrmed HSV CNS infection in young children throughout the British Isles. So that milder cases would be included, the deﬁnition of HSV CNS infection covered more than just serious neurologi- cal disease, which in turn comprised not only encephalitis but also severe illness with fever and convulsions. Thus only 58% of the children with HSV CNS infection in the survey had an illness that ﬁtted our strict deﬁnition of encephalitis as the remainder did not fulﬁl the criterion of encephalopathy for ≥24 h. Such atypical forms of HSV CNS infection have been previously reported2 3 and together with our ﬁndings show that HSV is responsible for more than clear- cut encephalitis in young children. Cases may have been missed in our survey because HSV DNA or pleocytosis may not be found in CSF soon after dis- ease onset. Likewise, aciclovir treatment may result in the absence of CSF HSV DNA and delay antibody seroconversion. Table 1 HSV CNS infection: results of laboratory investigations Patient no. CSF WBC (lymphocytes)/ RBC per µl Protein (g/l) Viral DNA* Intrathecal Seroconversion to antibody synthesis IgG or IgM† 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 7 (NT)/1310 35 (35)/3500 25 (25)/3 23 (18)/<1 93 (93)/295 2 (NT)/12 560 (280)/900§ 7 (NT)/50 70 (70)/40 21 (21)/115 97 (NK)/50¶ 120 (85)/2510 NT <1 (<1)/50 <1 (<1)/<1 1 (1)/10 NK (NK)/NK NT 10 (10)/37** 0.8 0.55 0.47 0.6 0.5 0.68 1.03 0.34 0.32 1.01 1.0 NT NT 0.23 NK 0.14 NK NT 1.06 HSV‡ HSV‡ HSV-1 Negative HSV-1 HSV‡ HSV-1 HSV-1 Negative HSV-1 HSV-1 HSV-1 NT HSV-1 HSV-1 HSV-1 HSV‡ NT HSV‡ NT NT NT NT NT NT NT NT Yes NT NT NT NT NT NT NT NT NT NT NT NT NT Yes NT Yes NT NT NT NT NT NT Yes NT NT NT NT Yes NT *Tested for by PCR. †Within 2 weeks of onset of serious neurological disease. ‡Virus not typed. §First CSF nothing abnormal detected. ¶First CSF clotted. **First sample WBC <1/RBC per µl 127. CNS, central nervous system; CSF, cerebrospinal ﬂuid; HSV, herpes simplex virus; NK, not known; NT, not tested; RBC, red blood cell; WBC, white blood cell. Arch Dis Child 2012;97:162–165. doi:10.1136/adc.2010.204677 163