Fifteen pediatric cases of suspected Japanese encephalitis (JE) were reported in Beijing Children's Hospital during the late summer of 2013. The clinical manifestations in most cases included high fever, seizures, and abnormal magnetic resonance imaging findings. Twelve of 15 cases were laboratory-confirmed as JE cases by pathogen identification. Epidemiological investigations showed that five of the 12 laboratory-confirmed patients had an incomplete JE vaccination history. Follow-up investigations after discharge indicated that seven laboratory-confirmed JE patients without JE vaccinations had relatively poor prognoses, with an average Modified Rankin Scale (MRS) score of 2.6 when compared with the other five laboratory-confirmed, JE-vaccinated patients with an average MRS score of 0.5. The observation of pediatric JE cases among those with a history of JE vaccination warrants further attention.

Japanese encephalitis (JE), one of the most serious viral encephalitis, is a mosquito-borne encephalitis induced by infection with Japanese encephalitis virus (JEV), which belongs to the genus Flavivirus, family Flaviviridae. JE remains a major health problem worldwide, especially in Asia, the Western Pacific, and Northern Australia, with approximately 70, 000 cases and 15, 000 deaths reported annually; 30%-50% survivors live with irreversible neurological damage^[1]. Infection with JEV is often asymptomatic, and children under 15 years of age are principally affected in endemic areas^[2].

JE immunization was initially implemented in the eastern coastal areas or relatively economically developed provinces in China since 1968 and has been included in 28 provinces (excluding Qinghai, Xinjiang, and Tibet) in national immunization programs since 2008^[2]. At the same time, improvements in laboratory diagnosis of JE have strengthened the quality of the clinical reports of JE cases. In recent years, there has been a marked decrease in the number of JE cases, from 10, 308 in 1996 to 2, 541 in 2010^[3].

According to JE incidence, Hebei Province is a low-endemic area in China with an annual reported number of JE cases ranging from 12 to 37 from 2007 to 2010. However, a JE outbreak of 234 cases was observed in Hebei Province in 2013. A similar situation was also observed in other areas of China, such as Shandong Province, with 407 cases reported in 2013^[4]. Owing to the close geographical distance between Hebei and Beijing and the better medical environment in Beijing, most serious cases, such as encephalitis, are referred to Beijing for medical treatment. Herein, we report the results of a systematic study of a cluster of pediatric JE patients reported in Hebei but hospitalized in Beijing Children’s Hospital, including their clinical manifestations, clinical outcomes, laboratory test results, JE vaccination history, and prognoses after discharge.

In accordance with the manual for JE diagnosis from the World Health Organization (WHO)^[5], we used the following definition in this study. A case of acute encephalitis syndrome (AES) was defined as a person of any age, at any time of year with the acute onset of fever and a change in mental status (including symptoms such as confusion, disorienta-tion, coma, or inability to talk) and/or new onset of seizures (excluding simple febrile seizures). Suspected JE was defined as an AES case that occurred during the JE epidemic. Laboratory-confirmed JE was defined as a suspected JE case for which there was laboratory confirmation of the presence of JEV-specific immunoglobulin M (IgM) in a single cerebrospinal fluid (CSF) or serum sample, detection of JEV RNA in the CSF using hemi-nested reverse transcriptase polymerase chain reaction (hnRT-PCR), or the isolation and identification of JEV from CSF.

In this study, 15 pediatric patients with suspected JE were hospitalized in Beijing Children’s Hospital from September 5 to October 8, 2013. They were all from Hebei Province, neighboring Beijing. The details of the patients’ history and clinical findings were recorded on standardized forms. Fever, seizures, behavioral abnormalities, focal weakness, and reflex changes were noted in all patients. The level of consciousness was assessed using the Glasgow coma scale (GCS). The patients showed a broad spectrum of clinical presentations ranging from brief illness lacking specific features to a protracted course of illness with varying severity. The clinical features of the 15 cases are shown in Table 1. High or moderate fever was the most common clinical feature and was observed in all cases. History of seizures was reported in the majority of patients (86.67%, 13/15), and 10 of the 15 children had seizures within 3 days of illness onset. The GCS scores ranged from 3 to 15 (mean, 10.8±1.32) at the time of hospitalization.

In cases of encephalitis, magnetic resonance imaging (MRI) is used to detect and evaluate the extent of lesions and to confirm or exclude a specific diagnosis. In this study, all patients underwent MRI of the brain using a 3.0 T scanner (Magnetom Avanto with Tim system; Siemens, Erlangen, Germany). T1-weighted [repetition time (TR)/echo time (TE)/excitation=500/50/3 ms], proton density (TR/TE/excitation=2000-2500/15-20/1 ms), and T2-weighted (TR/TE/excitation=4000/80-90/1 ms) images were obtained. Susceptibility-weighted and diffusion-weighted imaging were performed in multiple planes. From the results of MRI (Table S1 in the website of BES, www.besjournal.com), the lesions appeared hyperintense in fluid attenuated inversion recovery (FLAIR) and T2-weighted images and isointense to slightly hypointense in T1-weighted images. The MRI results were more frequently abnormal with involvement of the thalamus (12/15) and neocortex (8/15). Involvement of the basal ganglia and brainstem was observed in four patients. A hippocampal lesion was noted in one patient. MRI changes with thalamic involvement were closely correlated with the presence of dystonia. However, other clinical parameters, such as behavioral abnormalities, seizure, level of coma, and death, were not significantly correlated with radiological abnormalities.

In total, 13 serum and 13 CSF samples were collected during the acute phase from 15 patients after admission. In addition, six serum samples were collected during the convalescing stage. CSF samples were examined for protein, glucose, cells, bacteria, and fungi. The results showed significantly increased mean protein level (492.7±46.9 mg/L) and white blood cell count [(64.4±18.6) × 10⁶/L] (Table S1 in the website of BES, www.besjournal.com).

CSF and serum specimens were tested for suspected pathogens, including serological and molecular biological tests, virus isolation, and plaque reduction neutralization tests (PRNT). Based on the clinical diagnosis, JEV was the first pathogen to be tested. All serum samples were tested using a Panbio Japanese Encephalitis/Dengue IgM combo enzyme-linked immunosorbent assay (ELISA) kit (Panbio Diagnostics, Brisbane, Australia) and Beixi Japanese Encephalitis IgM ELISA kit (Shanghai B & C Biological Technology Co., Ltd., Shanghai, China) for JEV-specific antibodies. All CSF samples were tested using a Beixi Japanese Encephalitis IgM ELISA kit. For JEV IgM-negative specimens, we used ELISA IgM kits (Virion/Serion Co., Wurzburg, Germany) for other viral encephalitis pathogens, including echovirus (ECHOV), coxsackievirus (COXV), mumps virus, herpes simplex virus type 1 (HSV-1), HSV-2, varicella zoster virus (VZV), and measles virus. All procedures were performed in accordance with the respective manufacturer’s specifications. The results showed that 12 of the 15 patients had serum and/or CSF samples positive for anti-JEV IgM (Table 2). These 12 patients were defined as laboratory-confirmed JE cases. The other three patients negative for anti-JEV IgM were also negative for IgM antibodies to other etiological agents, including HSV, ECHOV, COXV, VZV, mumps virus, and measles virus (data not shown).

In this study, fever was the most common feature and was observed in all laboratory-confirmed JE cases. A history of seizures was observed in 83.3% (10/12) of JE patients, similar to previous studies. Additionally, no obvious difference was observed in the clinical manifestations between JE-positive and unknown cases. Combined with the MRI results, thalamic lesions were observed by MRI in 83.3% (10/12) of laboratory-confirmed JE patients, concordant with previous reports.

Thirteen CSF samples from 15 patients were examined by RT-PCR. RNA was extracted using a QIAamp viral RNA extraction kit (QIAGEN, Valencia, CA) in accordance with the manufacturer’s protocol, and first-strand cDNA was produced using Ready-To-Go You-Prime First-Strand Beads (Amersham Pharmacia Biotech, Piscataway, NJ) as described by the manufacturer. The JEV prM gene was amplified using hnRT-PCR. The target genes of EV71, CA16, and other enteroviruses were amplified using RT-PCR. One positive and one negative control were included in the reactions, and anticontamination procedures were strictly enforced. All of the procedures were performed according to the manufacturer’s specifications. Negative results were obtained for the genomes of suspected pathogens (Table 2), likely owing to the short period of viremia and low virus titer.

Leftover CSF specimens from 10 patients were tested for the presence of viruses as follows. The CSF samples were inoculated into monolayers of BHK-21 and C6/36 cells and incubated at 37 ℃ and 28 ℃, respectively. Cells were observed for a cytopathic effect (CPE) daily from days 1 to 7 after inoculation. Specimens that caused a CPE in three successive cell passages were regarded as positive isolates. No positive results were observed.

In accordance with the WHO recommendations, JE can be confirmed if a four-fold or greater increase in neutralizing anti-JEV antibody is observed in serum collected during the convalescent phase compared with those during the acute phase by PRNT. In this study, PRNT was performed on six convalescent sera and three available acute sera. Sera were tested in serial two-fold dilutions from 1 to 10. Diluted sera were mixed with equal volumes of culture medium containing JEV [P3 strain, 100 plaque-forming units (PFU)] and incubated at 37 ℃ for 1 hour. Six-well plates of confluent BHK-21 cells were inoculated with the serum-virus mixtures and incubated at 37 ℃ in a 5% CO₂ incubator for 1 h. Plates were overlaid with 3 mL of medium containing 0.8% agarose and again with 2.5 mL of second overlay medium containing neutral red vital stain (Sigma-Aldrich, St. Louis, MO). The neutralizing antibody titer was identified as the highest serum dilution that reduced the number of virus plaques in the test by≥90%. The results showed a four-fold increase in only one confirmed anti-JE IgM antibody-positive case (No. 4). No such increase was observed in the other two cases for which both convalescent and acute sera were available (Nos. 1 and 10). The neutralizing antibody titers of the other three cases for which only convalescent sera were available were 1:160, 1:160, and 1:40, respectively. The lack of a four-fold increase between convalescent and acute sera may have been owing to delayed specimen collection, as most of these cases were from rural areas and experienced complex hospitalization processes before their admission to Beijing Children’s Hospital.

Epidemiological retrospective investigations including health conditions, JE vaccination history, and prognosis after discharge were conducted. Information on outcome was recorded at 1, 3, 5, and 12 months after discharge from the hospital. The Modified Rankin Scale (MRS) was used to evaluate neurological function and outcome: 0=no symptoms, 1=no significant disability (able to carry out all usual activities despite some symptoms), 2=slight disability (able to look after their own affairs without assistance, but unable to carry out all previous activities), 3=moderate disability (requires some help, but able to walk independently), 4=moderately severe disability (unable to attend to own bodily needs without assistance, and unable to walk independently), 5=severe disability (requires constant nursing care and attention, bedridden, incontinent), and 6=dead.

Among the 15 pediatric patients, 14 were healthy before onset; one laboratory-confirmed JE patient had undergone resection of a cerebellar medulloblastoma 2 years previously and had recovered before the JE infection (No. 11) (Table 1).

Three patients died during the acute phase of illness, and all of the others patients were alive at the time of writing this report. Thus, the mortality rate was 20% (3/15). Moreover, two deaths among 12 patients with laboratory-confirmed JE were observed, representing a mortality rate of 16.67% (2/12), similar to previous reports. For example, the JE outbreak in Yuncheng City, Shanxi province had a mortality rate of 18%^[6], and a 6-month retrospective survey of patients with JE in Shandong Province, China reported a mortality rate of 17.7%-19.3%^[7]. However, the annual mortality rate reported in the notifiable disease system ranged from 2.51% to 4.66%^[8]. The lower reported mortality rate compared to the actual mortality rate is probably owing to a lack of follow-up and the occurrence of death after discharge. One laboratory-confirmed JE patient (No. 1) developed secondary anti-N-methyl-d-aspartate-receptor (NMDA-R) encephalitis 2 months after the onset of JE.

Six of the patients had a definite JE vaccination history (Table 3). Among them, five were laboratory-confirmed cases of JE. Of the five laboratory-confirmed JE patients with JE vaccination history, four had a single dose of the vaccine only and one had had two doses. This finding indicated that incomplete JE vaccination or only one dose may result in vaccination failure. The three patients who died had no history of JE vaccination.

The follow-up investigation (Table 3) showed that in the first month, the average MRS score of all patients was 3.7. At the 3-month follow-up, all of the patients showed an average MRS score reduction to 2.9. At the 5-month follow-up, the average MRS score of all patients was 2.3, and four had made a full recovery. At the 12-month follow-up, the average MRS score was 2.1, and six patients had fully recovered; five of these six fully recovered patients were laboratory-confirmed cases of JE. Moreover, among these five laboratory-confirmed patients, three had received JE vaccination several years previously; the MRS scores of the other two JE patients were 1 and 2, respectively. This finding indicated that three of the five laboratory-confirmed JE patients who had been vaccinated for JEV made full recoveries, and while the other two had better outcomes, with MRS scores of 1 and 2 at the 12-month follow-up, respectively. Although the outcomes did not differ significantly, the prognosis was relatively poor in the other seven laboratory-confirmed JE patients with no JE vaccination history, including two deaths, one with an MRS score of 5, two with an MRS score of 1, and two full recoveries at the 12-month follow-up.

Hebei Province administers a live attenuated SA14-14-2 JE vaccine with an immunization schedule of two doses, at 8 months and 2 years old, respectively^[9]. In this study, a few patients with JE had a JE vaccination history, suggesting that vaccination failure may have occurred owing to incomplete vaccination. However, the prognosis of patients with JE with a vaccination history was better than that of patients without vaccination, showing that vaccination could influence the clinical features and protect the patient from a severe clinical presentation even with only one dose. Most of the patients had no JE vaccination history, indicating that there is still a gap in JEV vaccination coverage. A previous study showed that integrating the JE vaccine into the Expanded Programme on Immunization (EPI) is a cost-effective investment^[10]. Therefore, complete vaccination coverage will be in urgent demand.

Although the clinical manifestations of JE cases in this study were similar to those of previous reports, the 12 months follow-up survey after discharge provided valuable data on JE prognoses, especially for the JE cases with a JE vaccination history. However, owing to the limited number of patients, a comprehensive study is necessary to validate these conclusions.