Influenza surveillance system of Japan and acute encephalitis and encephalopathy in the influenza season

Neurological features related to influenza virus in the pediatric population: a 3-year monocentric retrospective study

Influenza virus is generally characterized by fever, myalgia, and respiratory symptoms. Neurological entities have already been described, such as acute necrotizing encephalitis (ANE). We aimed to highlight the non-exceptional nature and explore the clinical spectrum and evolution of neurological features related to influenza virus in children. This monocentric observational study included patients under 18 years old, positive for influenza virus, between January 2017 and April 2019 in a pediatric university hospital. Patients were classified into two groups: those with or without a previous significant neurological or metabolic disorder. Two hundred eighty-nine children were identified with influenza infection. Thirty seven had a neurological manifestation: 14 patients who had previous significant neurological or metabolic disorder and 23 patients with no medical history. We identified several clinical patterns: 22 patients had seizures, 7 behavior disorders, 5 disturbances of consciousness, and 3 motor deficits. Four were diagnosed with a known influenza-associated neurological syndrome: 1 ANE, 1 cytotoxic lesion of the corpus callosum, 1 hemiconvulsion-hemiplegia-epilepsia syndrome, and 1 recurrent encephalitis in the context of a RANBP2 mutation. The neurological outcome was favorable in most cases. None of the patients with previous significant disorder retained sequalae or had a recurrence. Two patients had a fatal outcome, and both had a predisposing disorder.

CONCLUSION

Various neurological manifestations can be associated with influenza virus. Certain entities led to a poor prognosis, but in most cases, symptoms improved within a few days. The severity of the neurological manifestations correlated with previous neurological or metabolic disorders.

WHAT IS KNOWN

• Influenza viruses are well known pathogens with a seasonal epidemic evolution, particularly affecting children. These viruses cause acute fever with respiratory symptoms, associated with myalgia and headaches. Neurological presentation in influenza-virus infection is a well-established possibility as influenza virus is considered to be responsible for 27 to 36% of childhood encephalitis. Some specific and severe entity as acute necrotizing encephalitis, cytotoxic lesion of the corpus callosum, or Hemiconvulsion-hemiplegia-epilepsy syndrome are well described.

WHAT IS NEW

• In a French monocentric cohort of 37 children with influenza-related neurologic manifestations, the majority of these manifestations, including seizure, drowsiness, motor deficiency, hallucination… are self limiting and do not lead to after-effects. In rare cases (4/37), they may reveal severe encephalitis requiring rapid and appropriate treatment. Otherwise, comparison of a group of 14 children with underlying neurological or metabolic disorder with a group of 23 children free of any significant disorder show that the severity of the neurological manifestations was largely related to previous neurological or metabolic disorders highlighting the importance of vaccination in this population.

Comparing the cobas Influenza A/B Nucleic acid test for use on the cobas Liat System (Liat) with rapid antigen tests for clinical management of Japanese patients at the point of care

Background

Rapid diagnosis of influenza is critical in preventing the spread of infection and ensuring patients quickly receive antiviral medication to reduce the severity and duration of influenza symptoms, whilst controlling the spread of the causative virus. In Japan patients are often administered anti-influenza medication following a positive rapid antigen detection test (RADT) result. However, the sensitivity of RADTs can lead to false negative results. The cobas^® Influenza A/B Nucleic acid test for use on the cobas Liat^® System (Liat) is a molecular point-of-care method that can provide a more sensitive alternative to RADTs for rapid influenza diagnosis and treatment.

Methods

In this prospective multicenter study, diagnostic performance of the Liat test was compared with RADTs in patients presenting with influenza-like-illness. Test performance was also assessed by time since symptom onset.

Results

Of 419 patients enrolled, 413 were evaluable for all designated tests. Most patients had type-A infection, and only one patient had influenza type B. In 413 patients, the sensitivity and specificity (95% CI) of the Liat test were 99.5% (97.2–99.9%) and 99.5% (97.4–99.9%), respectively, and were 79.7% (73.5–84.7%) and 95.4% (91.7–97.5%) for RADTs. For patients tested <12 hours from symptom onset, the Liat test had significantly higher sensitivity than RADTs (p<0.0001).

Conclusion

Overall, compared with standard of care RADTs, the Liat test was more sensitive and specific in children and adults, particularly in the early stages of infection. Greater sensitivity can enable earlier diagnosis and may better inform appropriate antiviral treatment decisions.

Clinical features of the first critical case of acute encephalitis caused by avian influenza A (H5N6) virus

Highly pathogenic avian influenza viruses (HPAIV), such as H5N1, H5N6, and H7N9, have been reported to frequently infect humans, but acute encephalitis caused by HPAIV in humans has been rarely reported. We report the first critical case of acute encephalitis with mild pneumonia caused by the H5N6 virus. On January 25 of 2022, a 6-year-old girl with severe neurological symptoms was admitted to our hospital and rapidly developed into seizures and coma. Brain imaging showed abnormalities. Electroencephalogram (EEG) presented abnormal slow waves. Cerebrospinal fluid (CSF) contained elevated protein (1.64 g/L) and white cells (546 × 10⁶/L). Laboratory investigations revealed abnormally elevated transaminases, lactate dehydrogenase, and cytokines in serum. A novel reassortant H5N6 virus was identified from the patient’s serum, CSF, and tracheal aspirate specimens. Phylogenic analysis indicated that this virus was a novel reassortant avian-origin influenza A (H5N6) virus that belonged to clade 2.3.4.4b. This patient was diagnosed with acute encephalitis and discharged from the hospital accompanied by a language barrier. An epidemiological investigation confirmed that wild waterfowls were the direct source of infection in this case. Our study highlights the urgent need to pay attention to acute encephalitis caused by HPAIV.

An Association of Influenza Epidemics in Children With Mobile App Data: Population-Based Observational Study in Osaka, Japan

Background

Early surveillance to prevent the spread of influenza is a major public health concern. If there is an association of influenza epidemics with mobile app data, it may be possible to forecast influenza earlier and more easily.

Objective

We aimed to assess the relationship between seasonal influenza and the frequency of mobile app use among children in Osaka Prefecture, Japan.

Methods

This was a retrospective observational study that was performed over a three-year period from January 2017 to December 2019. Using a linear regression model, we calculated the R² value of the regression model to evaluate the relationship between the number of “fever” events selected in the mobile app and the number of influenza patients ≤14 years of age. We conducted three-fold cross-validation using data from two years as the training data set and the data of the remaining year as the test data set to evaluate the validity of the regression model. And we calculated Spearman correlation coefficients between the calculated number of influenza patients estimated using the regression model and the number of influenza patients, limited to the period from December to April when influenza is prevalent in Japan.

Results

We included 29,392 mobile app users. The R² value for the linear regression model was 0.944, and the adjusted R² value was 0.915. The mean Spearman correlation coefficient for the three regression models was 0.804. During the influenza season (December–April), the Spearman correlation coefficient between the number of influenza patients and the calculated number estimated using the linear regression model was 0.946 (P<.001).

Conclusions

In this study, the number of times that mobile apps were used was positively associated with the number of influenza patients. In particular, there was a good association of the number of influenza patients with the number of “fever” events selected in the mobile app during the influenza epidemic season.

Toll-like Receptors in Viral Encephalitis

Viral encephalitis is a rare but serious syndrome. In addition to DNA-encoded herpes viruses, such as herpes simplex virus and varicella zoster virus, RNA-encoded viruses from the families of Flaviviridae, Rhabdoviridae and Paramyxoviridae are important neurotropic viruses. Whereas in the periphery, the role of Toll-like receptors (TLR) during immune stimulation is well understood, TLR functions within the CNS are less clear. On one hand, TLRs can affect the physiology of neurons during neuronal progenitor cell differentiation and neurite outgrowth, whereas under conditions of infection, the complex interplay between TLR stimulated neurons, astrocytes and microglia is just on the verge of being understood. In this review, we summarize the current knowledge about which TLRs are expressed by cell subsets of the CNS. Furthermore, we specifically highlight functional implications of TLR stimulation in neurons, astrocytes and microglia. After briefly illuminating some examples of viral evasion strategies from TLR signaling, we report on the current knowledge of primary immunodeficiencies in TLR signaling and their consequences for viral encephalitis. Finally, we provide an outlook with examples of TLR agonist mediated intervention strategies and potentiation of vaccine responses against neurotropic virus infections.

Spatial learning and memory impaired after infection of non-neurotropic influenza virus in BALB/c male mice

During the influenza pandemic or seasonal influenza outbreak, influenza infection can cause acute influenza-associated encephalopathy/encephalitis (IAE), even death. Patients with severe IAE will also have severe neurological sequelae. Neurologic disorders have been demonstrated in the mice treated with peripheral influenza viruses infection, whether neurotropic or non-neurotropic viruses. However, previous studies focused on the acute phase of infection, and rarely paid attention to a longer range of observations. Therefore, the long-term effect of non-neurotropic virus infection on the host is not very clear. In this study, adult mice were infected with influenza virus H1N1/PR8. Then, spontaneous behavior, body weight, expression of cytokines in brain, spatial learning ability and spatial memory ability were observed, until the complete recovery period. The results showed that cytokines in the brain were highly expressed in the convalescent phase (14 day post inoculation, dpi), especially BDNF, IBA1, CX3CL1 and CD200 were still highly expressed in the recovery phase (28 dpi). Otherwise the emotional and spatial memory ability of mice were impacted in the convalescent phase (14 dpi) and the recovery phase (28 dpi). In brief, BALB/c mice infected with non-neurotropic influenza virus H1N1, the weight and motor ability decreased in acute stage. During the recovery period, the body weight and activity ability were completely restored, whereas the emotion disordered, and the ability of spatial learning and memory were impacted in the infected mice. This long-term behavior impact may be the lag injury caused by non-neurotropic influenza infection.

The relationship between seasonal influenza and telephone triage for fever: A population-based study in Osaka, Japan

Background

Replacing traditional surveillance with syndromic surveillance is one of the major interests in public health. However, it is unclear whether the number of influenza patients is associated with the number of telephone triages in Japan.

Methods

This retrospective, observational study was conducted over the six-year period between January 2012 to December 2017. We used the dataset of a telephone triage service in Osaka, Japan and the data on influenza patients published from the Information Center of Infectious Disease in Osaka prefecture. Using a linear regression model, we calculated Spearman’s rank-order coefficient and R² of the regression model to assess the relationship between the number of telephone triages for fever and the number of influenza patients in Osaka. Furthermore, we calculated Spearman’s rank-order coefficient and R² between the predicted weekly number of influenza patients from the linear regression model and the actual weekly number of influenza patients for influenza outbreak season (December-April).

Results

There were 465,971 patients with influenza, and the number of telephone triages for fever was 420,928 among 1,065,628 total telephone triages during the study period. Our analysis showed that the Spearman rank-order coefficient was 0.932, and R² and adjusted R² were 0.869 and 0.842, respectively. The Spearman rank-order coefficient was 0.923 (P<0.001) and R² was 0.832 in December-April (P<0.001).

Conclusion

We revealed a positive relationship in this population between the number of influenza patients and the number of telephone triages for fever.

Relationship between the number of pediatric patients with rotavirus and telephone triage for associated symptoms

BACKGROUND

Earlier syndromic surveillance may be effective in preventing the spread of infectious disease. However, there has been no research on syndromic surveillance for rotavirus. The study aimed to assess the relationship between the incidence of rotavirus infections and the number of telephone triages for associated symptoms in pediatric patients under 4 years old in Osaka prefecture, Japan.

METHODS

This was a retrospective observational study for which the study period was the 3 years between January 2015 and December 2017. We analyzed data on children under 4 years old who were triaged by telephone triage nurses using software. The primary endpoint was the number of rotavirus patients under 4 years triaged old per week. Using a linear regression model, we calculated the R square value of the regression model to assess the relationship between the number of patients with rotavirus and the number of telephone triages made for associated symptoms. Covariates in the linear regression model were the week number indicating seasonality and the weekly number of telephone triages related to rotavirus symptoms such as stomachache and vomiting.

RESULTS

During the study period, there were 102,336 patients with rotavirus, and the number of people triaged by telephone was 123,720. The highest correlation coefficient was 0.921 in the regression model with the number of telephone triages for "stomachache + nausea/vomiting" and "stomachache + diarrhea + nausea/vomiting".

CONCLUSION

The number of telephone triage symptoms was positively related to the incidence of pediatric patients with rotavirus in a large metropolitan area of Japan.

Latitudes mediate the association between influenza activity and meteorological factors: A nationwide modelling analysis in 45 Japanese prefectures from 2000 to 2018

BACKGROUND

Cold and dry conditions were well-documented as a major determinant of influenza seasonality in temperate countries but the association may not be consistent when the climate in temperate areas is closer to that in sub-tropical areas. We hypothesized latitudes may mediate the association between influenza activity and meteorological factors in 45 Japanese prefectures.

METHODS

We used the weekly incidence of influenza-like illness of 45 prefectures from 2000 to 2018 as a proxy for influenza activity in Japan, a temperate country lying off the east coast of Asia. A combination of generalized additive model and distributed lag nonlinear model was adopted to investigate the associations between meteorological factors (average temperature, relative humidity, total rainfall, and actual vapour pressure, a proxy for absolute humidity) and the influenza incidence. Kendall's tau b (τ) and Spearman correlation coefficient (r_s) between latitude and the adjusted relative risk (ARR) of each meteorological factor were also assessed.

RESULTS

A higher vapour pressure was significantly associated with a lower influenza risk but the ARR strongly weakened along with a lower latitude (τ = -0.23, p-value = 0.02; r_s = -0.33, p-value = 0.03). Lower temperature and lower relatively humidity were significantly associated with higher influenza risks in over 65% and around 40% of the prefectures respectively but the strength and significance of the correlations between their ARRs and latitude were weaker than that from vapour pressure.

CONCLUSION

Even though the range of latitudes in Japan is small (26°N-43°N), the relationships between meteorological factors and influenza activity were mediated by the latitude. Our study echoed absolute humidity played a more important role in relating influenza risk, but we on the other hand showed its effect on influenza activity could be hampered in a low-latitude temperate region, which have a warmer climate. These findings thus offer a high-resolution characterization of the role of meteorological factors on influenza seasonality.

Nationwide survey of influenza-associated acute encephalopathy in Japanese adults

BACKGROUND

Knowledge of adult patients with influenza-associated acute encephalopathy (IAE) is limited. We conducted a detailed survey to investigate the prevalence, clinical features, associated outcomes, and prognostic factors in adult IAE patients.

METHOD

A nationwide questionnaire on IAE patients was sent to the departments of Internal Medicine, Neurology, Neurosurgery, and Emergency and Critical Care at all hospitals with ≥200 beds in Japan.

RESULTS

118 patients were diagnosed with IAE during the 2013/14 to 2015/16 influenza seasons, and the estimated annual incidence of IAE in Japanese adults was 0.98/1000,000 population. 44 patients were subsequently enrolled in the detailed study. 93% of patients exhibited disturbance of consciousness. Convulsions and delirious behavior were present in 26% and 40% of patients, respectively. 65% of patients received pulse corticosteroid therapy with methylprednisolone and 21% of patients received intravenous gamma-globulin therapy. 63% of patients achieved a good recovery, but 7% died. Multiple logistic regression analysis revealed that plasma glucose level demonstrated a statistically significant association with poor outcome.

CONCLUSION

This nationwide survey provided data for the annual incidence and clinical features of IAE in Japanese adults. Hyperglycemia was indicated as an independent predictor of poor prognosis in IAE patients and reflected systemic hypercytokinemia in IAE pathogenesis.

Construction and evaluation of two computational models for predicting the incidence of influenza in Nagasaki Prefecture, Japan

It remains challenging to forecast local, seasonal outbreaks of influenza. The goal of this study was to construct a computational model for predicting influenza incidence. We built two computational models including an Autoregressive Distributed Lag (ARDL) model and a hybrid model integrating ARDL with a Generalized Regression Neural Network (GRNN), to assess meteorological factors associated with temporal trends in influenza incidence. The modelling and forecasting performance of these two models were compared using observations collected between 2006 and 2015 in Nagasaki Prefecture, Japan. In both the training and forecasting stages, the hybrid model showed lower error rates, including a lower residual mean square error (RMSE) and mean absolute error (MAE) than the ARDL model. The lag of log-incidence, weekly average barometric pressure, and weekly average of air temperature were 4, 1, and 3, respectively in the ARDL model. The ARDL-GRNN hybrid model can serve as a tool to better understand the characteristics of influenza epidemic, and facilitate their prevention and control.

Comparative epidemiology of influenza A and B viral infection in a subtropical region: a 7-year surveillance in Okinawa, Japan

BACKGROUND

The epidemic patterns of influenza B infection and their association with climate conditions are not well understood. Influenza surveillance in Okinawa is important for clarifying transmission patterns in both temperate and tropical regions. Using surveillance data, collected over 7 years in the subtropical region of Japan, this study aims to characterize the epidemic patterns of influenza B infection and its association with ambient temperature and relative humidity, in a parallel comparison with influenza A.

METHODS

From January 2007 until March 2014, two individual influenza surveillance datasets were collected from external sources. The first dataset, included weekly rapid antigen test (RAT) results from four representative general hospitals, located in the capital city of Okinawa. A nation-wide surveillance of influenza, diagnosed by RAT results and/or influenza-like illness symptoms, included the age distribution of affected patients and was used as the second dataset. To analyze the association between infection and local climate conditions, ambient temperature and relative humidity during the study period were retrieved from the Japanese Meteorological Agency website.

RESULTS

Although influenza A maintained high number of infections from December through March, epidemics of influenza B infection were observed annually from March through July. The only observed exception was 2010, when the pandemic strain of 2009 dominated. During influenza B outbreaks, influenza patients aged 5 to 9 years old and 10 to 14 years old more frequently visited sentinel sites. Although both ambient temperature and relative humidity are inversely associated with influenza A infection, influenza B infection was found to be directly associated with high relative humidity.

CONCLUSION

Further studies are needed to elucidate the complex epidemiology of influenza B and its relationship with influenza A. In the subtropical setting of Okinawa, epidemics of influenza B infection occur from March to July following the influenza A epidemic, and primarily affect school-age children. These findings help to define unknown aspects of influenza B and can inform healthcare decisions for patients located outside temperate regions.

Japanese Surveillance Systems and Treatment for Influenza

Influenza management and surveillance programs in Japan possess several unique features. The national influenza surveillance is affiliated with National Epidemiological Surveillance for Infectious Diseases (NESID) and features sentinel outpatient surveillance, virological surveillance, and reports on hospitalization, mortality, and influenza-associated encephalopathy. Of note, information on the number of student absences and class/grade/school closures due to influenza are also reported to the government and made publically available. A private online influenza surveillance portal by volunteer doctors provides a real-time information source for the Japanese clinicians and the general public. For influenza treatment, three classes of drugs are approved and covered by national medical insurance in Japan: M2 inhibitors, neuraminidase inhibitors (NAIs), and a polymerase inhibitor. Four NAIs, oseltamivir, zanamivir, laninamivir, and peramivir, are licensed in Japan and are prescribed to seven to eight million patients annually. NAIs are prescribed to any influenza outpatient rather than being limited to severe cases. The majority (80-95 %) of patients start the treatment within 48 h of onset. Laninamivir and peramivir were used almost solely in Japan, until the approval of the latter drug by the FDA. Observational studies showed that the two drugs have equal effectiveness as oseltamivir and zanamivir. The Japanese approach to influenza surveillance and management has facilitated bringing new influenza antivirals to the markets and has driven innovative research in this field. New classes of antivirals, including polymerase inhibitors and cap-dependent endonuclease inhibitor, provide novel tools for treatment of influenza in Japan and the rest of the world.

Influenza newspaper reports and the influenza epidemic: an observational study in Fukuoka City, Japan

OBJECTIVES

We examined whether the weekly number of newspaper articles reporting on influenza was related to the incidence of influenza in a large city.

DESIGN

Prospective, non-randomised, observational study.

SETTING

Registry data of influenza cases in Fukuoka City, Japan.

PARTICIPANTS

A total of 83,613 cases of influenza cases that occurred between October 1999 and March 2007 in Fukuoka City, Japan.

MAIN OUTCOME MEASURE

A linear model with autoregressive time series errors was fitted to time series data on the incidence of influenza and the accumulated number of influenza-related newspaper articles with different time lags in Fukuoka City, Japan. In order to obtain further evidence that the number of newspaper articles a week with specific time lags is related to the incidence of influenza, Granger causality was also tested.

RESULTS

Of the 16 models including 'number of newspaper articles' with different time lags between 2 and 17 weeks (xt-2 to t-17), the β coefficients of 'number of newspaper articles' at time lags between t-5 and t-13 were significant. However, the β coefficients of 'number of newspaper articles' that are significant with respect to the Granger causality tests (p<0.05) were the weekly number of newspaper articles at time lags between t-6 and t-10 (time shift of 10 weeks, β=-0.301, p<0.01; time shift of 9 weeks, β=-0.200, p<0.01; time shift of 8 weeks, β=-0.156, p<0.01; time shift of 7 weeks, β=-0.122, p<0.05; time shift of 6 weeks, β=-0.113, p<0.05).

CONCLUSIONS

We found that the number of newspaper articles reporting on influenza in a week was related to the incidence of influenza 6-10 weeks after media coverage in a large city in Japan.

Neurologic manifestations and complications of pandemic influenza A H1N1 in Malaysian children: what have we learnt from the ordeal?

INTRODUCTION

In 2009, pandemic influenza A H1N1 emerged in Mexico and subsequently spread worldwide. In Malaysia, there were more than a thousand of confirmed cases among children. The general clinical characteristics of these children have been well-published. However, the description of neurologic complications is scarce.

OBJECTIVE

This study aims to describe the characteristics of neurologic manifestations and complications in a national paediatric cohort with pandemic influenza A H1N1.

METHODS

During the pandemic, children (12 years or less) admitted for novel influenza A H1N1 in 68 Malaysian public hospitals, were prospectively enrolled into national database. The clinical, laboratory and neuro-imaging data for children with neurologic manifestations, hospitalized from 15th June 2009 till 30th November 2009, was reviewed.

RESULTS

Of 1244 children with influenza A H1N1 during the study period, 103 (8.3%) presented with influenza-related neurological manifestations. The mean age of our study cohort was 4.2 years (SD: 3.3 years). Sixty percent of them were males. Sixty-nine (66.9%) were diagnosed as febrile seizures, 16 (15.5%) as breakthrough seizures with underlying epilepsy, 14 (13.6%) as influenza-associated encephalopathy or encephalitis (IAE) and 4 (3.9%) as acute necrotizing encephalopathy of childhood (ANEC). All 4 available CSF specimens were negative for influenza viral PCR. Among 14 children with brain-imaging done, 9 were abnormal (2: cerebral oedema, 4: ANEC and 3: other findings). There were four deaths and three cases with permanent neurological sequelae.

CONCLUSION

About one-tenth of children with pandemic influenza A H1N1 presented with neurologic complications. The most common diagnosis was febrile seizures. One-fifth of those children with neurologic presentation had IAE or ANEC, which carried higher mortality and morbidity. This large national study provides us useful data to better manage children with neurologic complications in the future pandemic influenza outbreaks.

Investigation of an Influenza A (H3N2) outbreak in evacuation centres following the Great East Japan earthquake, 2011

Background

The Great East Japan Earthquake of magnitude 9.0 that struck on 11 March 2011 resulted in more than 18000 deaths or cases of missing persons. The large-scale tsunami that followed the earthquake devastated many coastal areas of the Tohoku region, including Miyagi Prefecture, and many residents of the tsunami-affected areas were compelled to reside in evacuation centres (ECs). In Japan, seasonal influenza epidemics usually occur between December and March. At the time of the Great East Japan Earthquake on 11 March 2011, influenza A (H3N2) was still circulating and there was a heightened concern regarding severe outbreaks due to influenza A (H3N2).

Methods

After local hospital staff and public health nurses detected influenza cases among the evacuees, an outbreak investigation was conducted in five ECs that had reported at least one influenza case from 23 March to 11 April 2011. Cases were confirmed by point-of-care tests and those residues were obtained and subjected to reverse transcription PCR and/or real time RT-PCR for sub-typing of influenza.

Results

There were 105 confirmed cases detected during the study period with a mean attack rate of 5.3% (range, 0.8%–11.1%). An epidemiological tree for two ECs demonstrated same-room and familial links that accounted for 88.5% of cases. The majority of cases occurred in those aged 15-64 years, who were likely to have engaged in search and rescue activities. No deaths were reported in this outbreak. Familial link accounted for on average 40.5% of influenza cases in two ECs and rooms where two or more cases were reported accounted for on average 85% in those ECs. A combination of preventative measures, including case cohorting, personal hygiene, wearing masks, and early detection and treatment, were implemented during the outbreak period.

Conclusions

Influenza can cause outbreaks in a disaster setting when the disaster occurs during an epidemic influenza season. The transmission route is more likely to be associated with sharing room and space and with familial links. The importance of influenza surveillance and early treatments should be emphasized in EC settings for implementing preventive control measures.

Neurological manifestations of influenza infection in children and adults: results of a National British Surveillance Study

BACKGROUND

The emergence of influenza A(H1N1) 2009 was met with increased reports of associated neurological manifestations. We aimed to describe neurological manifestations of influenza in adults and children in the United Kingdom that presented at this time.

METHODS

A 2-year surveillance study was undertaken through the British adult and pediatric neurological surveillance units from February 2011. Patients were included if they met clinical case definitions within 1 month of proven influenza infection.

RESULTS

Twenty-five cases were identified: 21 (84%) in children and 4 (16%) in adults. Six (29%) children had preexisting neurological disorders. Polymerase chain reaction of respiratory secretions identified influenza A in 21 (81%; 20 of which [95%] were H1N1) and influenza B in 4 (15%). Twelve children had encephalopathy (1 with movement disorder), 8 had encephalitis, and 1 had meningoencephalitis. Two adults had encephalopathy with movement disorder, 1 had encephalitis, and 1 had Guillain-Barré syndrome. Seven individuals (6 children) had specific acute encephalopathy syndromes (4 acute necrotizing encephalopathy, 1 acute infantile encephalopathy predominantly affecting the frontal lobes, 1 hemorrhagic shock and encephalopathy, 1 acute hemorrhagic leukoencephalopathy). Twenty (80%) required intensive care, 17 (68%) had poor outcome, and 4 (16%) died.

CONCLUSIONS

This surveillance study described a cohort of adults and children with neurological manifestations of influenza. The majority were due to H1N1. More children than adults were identified; many children had specific encephalopathy syndromes with poor outcomes. None had been vaccinated, although 8 (32%) had indications for this. A modified classification system is proposed based on our data and the increasing spectrum of recognized acute encephalopathy syndromes.

National surveillance of influenza-associated encephalopathy in Japan over six years, before and during the 2009-2010 influenza pandemic

Influenza-associated encephalopathy (IAE) is a serious complication of influenza and is reported most frequently in Japan. This paper presents an assessment of the epidemiological characteristics of influenza A (H1N1) 2009-associated encephalopathy in comparison to seasonal IAE, based on Japanese national surveillance data of influenza-like illness (ILI) and IAE during flu seasons from 2004–2005 through 2009–2010. In each season before the pandemic, 34–55 IAE cases (mean 47.8; 95% confidence interval: 36.1–59.4) were reported, and these cases increased drastically to 331 during the 2009 pandemic (6.9-fold the previous seasons). Of the 331 IAE cases, 322 cases were reported as influenza A (H1N1) 2009-associated encephalopathy. The peaks of IAE were consistent with the peaks of the influenza epidemics and pandemics. A total of 570 cases of IAE (seasonal A, 170; seasonal B, 50; influenza A (H1N1) 2009, 322; unknown, 28) were reported over six seasons. The case fatality rate (CFR) ranged from 4.8 to 18.2% before the pandemic seasons and 3.6% in the 2009 pandemic season. The CFR of pandemic-IAE was 3.7%, which is lower than that of influenza A−/B-associated encephalopathy (12.9%, p<0.001; 14.0%, p = 0.002; respectively). The median age of IAE was 7 years during the pandemic, which is higher than that of influenza A−/B-associated encephalopathy (4, p<0.001; 4.5, p = 0.006; respectively). However, the number of pandemic-IAE cases per estimated ILI outpatients peaked in the 0–4-year age group and data both before and during the pandemic season showed a U-shape pattern. This suggests that the high incidence of influenza infection in the 0–4 year age group may lead to a high incidence of IAE in the same age group in a future influenza season. Further studies should include epidemiologic case definitions and clinical details of IAE to gain a more accurate understanding of the epidemiologic status of IAE.

Post-marketing assessment of neuropsychiatric adverse events in influenza patients treated with oseltamivir: an updated review

A 2008 review by our group concluded that the risk of neuropsychiatric adverse events (NPAEs) in influenza patients was not increased by oseltamivir exposure, and did not identify any mechanism by which oseltamivir or its metabolites could cause or worsen such events. The current article reviews new information on this topic. Between September 16, 2007 and May 15, 2010, 1,805 spontaneously-reported NPAEs were identified in 1,330 patients receiving oseltamivir: 767 (42.5%) from Japan, 296 (16.4%) from the USA, and 742 (41.1%) from other countries. NPAEs were more common in children: 1,072 (59.4%) events were in those aged ≤16 years. NPAEs often occurred within 48 h of treatment initiation (953 events; 52.8%). Nearly half of the events were serious in nature (838; 46.4%). The three largest categories of events were abnormal behavior (457 events, 25.3%), miscellaneous psychiatric events (370; 20.5%), and delusions/perceptual disturbances (316 events, 17.5%). A total of 1,545 events (85.6%) in eight different categories were considered to be delirium or delirium-like. Twenty-eight suicide-related events were reported. A US healthcare claims database analysis showed that the risk of NPAEs in 7,798 oseltamivir-treated patients was no higher than that in 10,411 patients not on antivirals, but a study on oseltamivir and abnormal behavior in Japan was less conclusive. NPAE frequency in oseltamivir-exposed Japanese and Taiwanese children with influenza was the same as in unexposed children. New analysis of the UK General Practice Research Database showed that the relative adjusted risk of NPAEs in influenza patients was 2.18-times higher than in the general population. Other epidemiology studies report frequent occurrence of encephalitis and similar disorders in influenza patients independently of oseltamivir exposure. The new data support the findings of the original assessment. Evidence suggests that influenza-related encephalopathies are caused by influenza-induced inflammatory responses, but more work is needed to confirm the underlying mechanisms.

Acute encephalopathy with pandemic (H1N1) 2009 virus infection

OBJECTIVES

In April 2009, a novel influenza A (H1N1) pdm virus was identified in Mexico and spread quickly around the world. However, the clinical features of acute encephalopathy associated with 2009 pandemic influenza have not yet been elucidated.

METHODS

We treated 8 patients (3 boys and 5 girls) aged 4 to 11 years (average age, 8 y 3 months) with influenza virus-associated encephalopathy, who presented at our 2 hospitals between July 2009 and March 2010. We investigated the clinical characteristics, treatments, and outcomes in the patients.

RESULTS

In all patients, brain computed tomography showed mild to severe diffuse cerebral edema, and electroencephalography revealed diffuse high-voltage slow waves. They were all treated with oseltamivir and methylprednisolone pulse therapy. Six patients recovered without any sequelae; however, the remaining 2 had residual neurological sequelae. These 2 patients presented with severe disturbance of consciousness, and their central nervous system symptoms appeared within 12 hours after the onset of fever. One patient had periventricular leukomalacia and symptomatic epilepsy by perinatal brain hypoxia, and the other patient had 1 complex febrile and 2 febrile seizures.

CONCLUSIONS

This study showed that patients with influenza-associated encephalopathy caused by influenza A (H1N1) pdm infection were all older than those with seasonal influenza. Underlying neurological disease or history may be associated with poor prognosis.

Influenza A 2009 H1N1 encephalitis in adults with viral RNA in cerebrospinal fluid

We present 3 cases of influenza A 2009 H1N1 encephalitis occurring in adults, corroborated by viral genome detection in cerebrospinal fluid (CSF) and evidence of meningeal inflammation on brain histopathology. This paper emphasizes the possibility of viral detection in CSF and stresses the lack of an effective treatment for neurological manifestations of influenza.

Oseltamivir in seasonal, pandemic, and avian influenza: a comprehensive review of 10-years clinical experience

Oseltamivir (Tamiflu®; F. Hoffmann-La Roche Ltd, Basel, Switzerland) is an orally administered antiviral for the treatment and prevention of influenza A and B infections that is registered in more than 100 countries worldwide. More than 83 million patients have been exposed to the product since its introduction. Oseltamivir is recommended by the World Health Organization (WHO) for use in the clinical management of pandemic and seasonal influenza of varying severity, and as the primary antiviral agent for treatment of avian H5N1 influenza infection in humans. This article is a nonsystematic review of the experience gained from the first 10 years of using oseltamivir for influenza infections since its launch in early 2000, emphasizing recent advances in our understanding of the product and its clinical utility in five main areas. The article reviews the pharmacokinetics of oseltamivir and its active metabolite, oseltamivir carboxylate, including information on special populations such as children and elderly adults, and the co-administration of oseltamivir with other agents. This is followed by a summary of data on the effectiveness of oseltamivir treatment and prophylaxis in patients with all types of influenza, including pandemic (H1N1) 2009 and avian H5N1 influenza. The implications of changes in susceptibility of circulating influenza viruses to oseltamivir and other antiviral agents are also described, as is the emergence of antiviral resistance during and after the 2009 pandemic. The fourth main section deals with the safety profile of oseltamivir in standard and special patient populations, and reviews spontaneously reported adverse event data from the pandemic and pre-pandemic periods and the topical issue of neuropsychiatric adverse events. Finally, the article considers the pharmacoeconomics of oseltamivir in comparison with vaccination and usual care regimens, and as a component of pandemic influenza mitigation strategies.

The interplay of infection and genetics in acute necrotizing encephalopathy

PURPOSE OF REVIEW

Acute necrotizing encephalopathy (ANE) presents with fulminant encephalopathy and characteristic brain lesions following viral infection. The rarity and unpredictability of the disorder have significantly impaired its study. Growing recognition of ANE and the discovery of causative missense mutations in the nuclear pore gene RANBP2 give promising steps toward unraveling this disease. This review summarizes recent advances of clinical and scientific understanding of ANE.

RECENT FINDINGS

Inflammatory factors participate in the pathogenesis of ANE, but the lack of difference between influenza and noninfluenza ANE focuses attention on the abnormal host response as causative. Early treatment with steroids provides the best outcome for patients who do not have brainstem lesions. Missense mutations in RANBP2 cause the majority of familial and recurrent ANE cases, but other single-gene causes of ANE are possible for familial, recurrent, and sporadic cases.

SUMMARY

Early recognition and systematic evaluation of ANE are necessary. Modeling ANE as a genetic disorder may provide the most immediate gains in the understanding and treatment of ANE and related disorders.

Acute encephalopathy and encephalitis caused by influenza virus infection

PURPOSE OF REVIEW

Influenza-associated acute encephalopathy/encephalitis (IAE) is an uncommon but serious complication with high mortality and neurological sequelae. This review discusses recent progress in IAE research for a better understanding of the disease features, populations, outcomes, diagnosis, and pathogenesis.

RECENT FINDINGS

In recent years, many IAE cases were reported from many countries, including Japan, Canada, Australia, Austria, The Netherlands, United States, Sweden, and other countries and regions. During the novel influenza A/H1N1 pandemic, many IAE cases with A/H1N1 infection in children were reported, particularly in those hospitalized with influenza infection. Pathogenesis of IAE is not fully understood but may involve viral invasion of the CNS, proinflammatory cytokines, metabolic disorders, or genetic susceptibility. An autosomal dominant viral acute necrotizing encephalopathy (ANE) was recently found to have missense mutations in the gene Ran-binding 2 (RANBP2). Another recurrent ANE case following influenza A infection was also reported in a genetically predisposed family with an RANBP2 mutation.

SUMMARY

Although IAE is uncommon, compared with the high incidence of influenza infection, it is severe. However, this complication is not duly recognized by health practitioners. Recent advances highlight the threat of this complication, which will help us to have a better understanding of IAE.

Posterior reversible encephalopathy syndrome and cerebral vasculopathy associated with influenza A infection: report of a case and review of the literature

BACKGROUND AND PURPOSE

Influenza A infection can precipitate encephalopathy, encephalitis, or Reye syndrome with the development of cerebral edema in children and is associated with an increased incidence of stroke in adults. The mechanism of these events is poorly understood. Posterior reversible encephalopathy syndrome (PRES) is seen in association with infection/sepsis, and cerebral vasculopathy has been demonstrated in PRES. We describe a case of PRES that develops in association with influenza A.

SUMMARY OF CASE

A normotensive 65-year-old woman presented with altered mentation and nausea in the setting of a viral prodromal illness ultimately confirmed as influenza A. Posterior reversible encephalopathy syndrome developed on the second day after admission. Catheter cerebral angiogram documented vasculopathy in PRES-involved regions with areas of focal vessel dilatation and string-of-bead appearance.

CONCLUSIONS

The association between influenza A and PRES with documentation of cerebral vasculopathy suggests a common systemic vascular mechanism behind PRES and influenza-related encephalopathic edema and stroke.

PRIMARY BIOMARKERS IN CEREBRAL SPINAL FLUID OBTAINED FROM PATIENTS WITH INFLUENZA-ASSOCIATED ENCEPHALOPATHY ANALYZED BY METABOLOMICS

In order to search for the specific biomarkers of patients with influenza-associated encephalopathy this article analyzed all metabolites in cerebrospinal fluid (CSF) by using metabolome analysis. In all metabolites, the peaks of two molecular weights, 246.0092 and 204.0611, were significantly higher than those in other diseases including influenza without convulsion (p < .05). The peak of a molecular weight 228.0247 in all of the patients except one was less than that in other patients. These results indicate that the new metabolites detected in CSF would be primary markers for the diagnosis of influenza-associated encephalopathy.

Spatial and temporal dynamics of influenza outbreaks

BACKGROUND

Annual influenza epidemics occur worldwide, resulting in considerable morbidity, mortality, and economic burden. Despite this regular occurrence, few studies have systematically examined the regional spatiotemporal patterns of influenza outbreaks.

METHODS

Weekly incidence data for influenza cases in Fukuoka Prefecture (Japan) from 29 August 2005 to 3 June 2007 (n = 113,503) were geocoded at sentinel medical institutions (mainly pediatric hospitals and clinics). Space-time permutation scan statistics were then used to identify weekly temporal and spatial clusters of reported cases of influenza during the 2006-2007 influenza season.

RESULTS

In the early phase of the influenza season, clusters were detected in the Fukuoka and Kitakyushu urban areas. The clusters then diffused gradually and spread into the rural areas of Fukuoka Prefecture. After a period of middle- to large-scale epidemic, the outbreak gradually waned.

CONCLUSIONS

Based on the permutation model, space-time permutation scan statistics can play an important role in detecting influenza outbreaks at an early stage and identifying the spatiotemporal patterns of geographic spread.

Urinary organic metabolite screening of children with influenza-associated encephalopathy for inborn errors of metabolism using GC/MS

BACKGROUND

Influenza-associated encephalopathy (IAE) occurs in childhood often with a serious clinical course and fatal outcomes. We screened children with IAE using GC/MS to determine whether they have metabolic disorders such as organic acidemias.

METHODS

Urine samples from 70 Japanese children with IAE were analyzed between 2001 and 2005 using GC/MS with solvent extraction and direct drying methods.

RESULTS

Apparent metabolic disorders in 6 of 70 tested children included vitamin B12-responsive methylmalonic acidemia (MMA; n=1), fructose-1,6-diphosphatase (FDPase) deficiency (n=1) and non-ketotic dicarboxylic aciduria (n=4) suggesting disorders of fatty acid oxidation. One child had an FDPase deficiency, for which glycerol infusion was contraindicated. Valproic acid metabolites were detected in 10 children and urinary glycerol excretion was increased in 22 of them after glycerol treatment.

DISCUSSION

Our results showed that inborn errors of metabolism (IEM), such as organic acidemias, are detectable among children with IAE. Patients with metabolic disorders such as an FDPase deficiency and MMA often have hypoglycemia, hyperammonemia and acute lactic acidemia. Importantly, a detection of FDPase deficiency in which glycerol infusion is contraindicated suggests careful selection of a treatment strategy for "acute encephalopathy". We detected valproic acid and its metabolites at a rate of 14%, which was considerably higher than that in a control population. Thus, convulsive disorders might be a risk factor associated with IAE.

Design and prototype of a mechanism for active on-line emerging/notifiable infectious diseases control, tracking and surveillance, based on a national healthcare card system

Timeliness is a critical issue in preventing the spread of emerging/notifiable infectious diseases, such as severe acute respiratory syndrome (SARS) or avian influenza (bird flu). Current computerized surveillance systems in many countries have demonstrated their usefulness in detecting specified communicable-diseases. However, the off-line, daily or weekly data reporting mode induces a time lag in data collection, transmission, processing, and responses. This paper proposes an on-line real-time mechanism, named EDICTS, for emerging/notifiable infectious diseases control, tracking and surveillance. It is based on the on-line health IC card system and works at the registration process of primary care practices and emergency departments. Hence, should a disease defined by CDC (Center for disease control) be detected at the registration station, EDICTS responds in real time. Note that EDICTS is a mechanism; it is CDC that determines the policy and activates it. A prototype is designed and implemented on a simulated environment of the Taiwan's national health insurance IC card system. The proposed policy and rules are defined according to the CDC regulations. Timely, sensitive and cost-effective, EDICTS complements the existing successive level of CDC reporting system as a fast-response control channel.

A missense mutation of the Toll-like receptor 3 gene in a patient with influenza-associated encephalopathy

Toll-like receptors (TLRs) recognize pathogen-associated molecular patterns and mediate the activation of NF-kappaB and the production of proinflammatory cytokines, which is critical for the innate immune system. TLR3 recognizes both double-stranded RNA and the influenza A virus. Since influenza-associated encephalopathy is frequent in Japan and East Asia and its pathological mechanism remains unknown, we analyzed several genes including TLRs and the retinoic acid inducible gene I, which could be involved in the recognition of the RNA virus. In one of three patients with influenza-associated encephalopathy, we detected a novel missense mutation (F303S) in just the TLR3 gene. This was confirmed as a loss-of-function mutant in a dose-dependent manner by NF-kappaB and IFN-beta reporter assays using wild-type and mutant TLR3-transfected HEK293 cells. Our results imply that a mutation of the TLR3 gene could be one of the factors responsible for influenza-associated encephalopathy.

Apoptosis under hypercytokinemia is a possible pathogenesis in influenza-associated encephalopathy

BACKGROUND

Influenza-associated encephalopathy is reported to be frequent in Japan and East Asia. No evaluating markers except interleukin (IL)-6 and tumor necrosis factor (TNF)-alpha and no likely pathological mechanism for the disease have yet been elucidated.

METHODS

In this study, influenza-associated encephalopathy was defined by clinical symptoms, and the use of an anti-influenza antibody test and/or influenza antigen detection kits, as well as computed tomography and/or magnetic resonance imaging. The levels of proinflammatory cytokines, acute phase proteins, endothelial markers and cytochrome c were compared in sera from 11 patients with and 42 without encephalopathy.

RESULTS

Cytochrome c concentration in sera from patients with encephalopathy was markedly increased compared with that from patients without encephalopathy and normal controls. Although levels of several other proinflammatory cytokines and acute phase proteins such as TNF-alpha and IL-8 were also elevated in patients with influenza virus infection, the difference between those with and without encephalopathy, though significant, was less dramatic. The mean serum concentration of cytochrome c in 11 patients with encephalopathy, consisting of four deceased, four with and three without residual central nervous system sequelae, was 26.7 +/- 19.5 ng/mL on admission. In contrast, cytochrome c levels in 42 patients without encephalopathy were 0.3 +/- 0.7 ng/mL.

CONCLUSION

The present results indicate that cytochrome c is a useful marker to follow patients with influenza-associated encephalopathy and suggest that an apoptosis of cells in several organs including the cerebrum and liver under the influence of hypercytokinemia is a possible mechanism of the disease.

Nitrite/Nitrate (NOx) and Zinc Concentrations in Influenza-associated Encephalopathy in Children with Different Sequela

NOx (NO2 and NO3) in CSF obtained from 22 patients with influenza-associated encephalopathy were higher than those of a control group. Within the different prognosis, there were no significant differences in NOx levels. By analyzing the serum obtained from patients infected with influenza, including encephalopathy, with others, the serum zinc levels did show marked differences between them. Four out of eleven patients with influenza-associated encephalopathy showed low zinc levels below the normal range. However, there were no significant differences in the zinc levels between the group with sequela and without sequela. These results indicate that the increase of NOx levels detected in influenza-associated encephalopathy relates to the low zinc levels, and both low molecules might play an important role for the cause of encephalopathy.

An adult autopsy case of acute encephalopathy associated with influenza A virus

On a cold winter morning, a 35-year-old male was unexpectedly found dead and therefore autopsied. Macro- and microscopically, the lungs were demonstrated bronchopneumonia. On the surface of brain, small blood vessels were slightly congested. Microscopically, brain edema was also observed, and proliferation of lymphocytes was observed around the capillary vessels of the hippocampus. These findings suggested a viral infection of the cerebrum. We conducted an immunohistochemical study with antibody against influenza virus. Influenza A virus antigen was detected in both the lungs and brain. Therefore, findings were compatible with influenza A encephalopathy. Even when serological inspection is not performed, it is useful to inspect localization of the virus antigen immunohistochemically. We considered that it is necessary to perform pathological examination for influenza encephalopathy in sudden death cases when influenza is epidemic.

Geographic and temporal trends in influenzalike illness, Japan, 1992-1999

Kriging analysis improved visualization and understanding of trends in seasonal ILI activity in Japan.

From 1992 to 1999, we analyzed >2.5 million cases of influenzalike illness (ILI). Nationwide influenza epidemics generally lasted 3–4 months in winter. Kriging analysis, which illustrates geographic movement, showed that the starting areas of peak ILI activity were mostly found in western Japan. Two spreading patterns, monotonous and multitonous, were observed. Monotonous patterns in two seasons featured peak ILI activity that covered all of Japan within 3 to 5 weeks in larger epidemics with new antigenic variants of A/H3N2. Multitonous patterns, observed in the other five seasons, featured peak ILI activity within 12 to 15 weeks in small epidemics without new variants. Applying the kriging method allowed better visualization and understanding of spatiotemporal trends in seasonal ILI activity. This method will likely be an important tool for future influenza surveillance in Japan.

Influenza virus and CNS manifestations

Neurological involvement during influenza infection has been described during epidemics and is often consistent with serious sequelae or death. An increasing incidence of influenza-associated encephalitis/encephalopathy has been reported in Japan, mainly in children. A variety of other clinical CNS manifestations, such as Reye's syndrome, acute necrotising encephalopathy (ANE), and myelitis as well as autoimmune conditions, such as Guillain-Barre's syndrome, may occur during the course of influenza infection. Virological diagnosis is essential and based on virus isolation, antigen detection, RNA detection by PCR, and serological analyses. Neuroimaging with CT and MRI of the brain are of prognostic value. The pathogenic mechanisms behind the influenza CNS complications are unknown. The treatment is symptomatic, with control of vital functions in the intensive care unit, antiepileptic medication and treatment against brain oedema.

Encephalopathy associated with influenza A

We report a 3-year-old boy with influenza A virus-associated encephalopathy. The diagnosis was based on clinical findings, magnetic resonance imaging, repeated isolation of influenza A virus from nasopharyngeal aspirate and seroconversion between acute and convalescent sera. The clinical picture was characterized by fever and aphasia followed by seizures and a rapid deterioriation of consciousness 2 days later. This patient illustrates that influenza A-associated encephalopathy with severe neurological deficit can occur with atypical distribution of brain lesions during the course of the illness, while initial brain MRI and laboratory findings of cerebrospinal fluid are normal, including reverse transcription polymerase chain reaction.

Effect of mass immunization against influenza encephalopathy on mortality rates in children

BACKGROUND

Since the Japanese influenza vaccination program for school children was terminated in 1994, a steep rise has been noted in the number of young children reported with fulminant influenza and influenza associated with acute encephalopathy/encephalitis. The purpose of the present study was to interpret and clarify the effect of mass influenza vaccination on mortality of Japanese children, aged <19 years, with influenza and influenza-associated acute encephalopathy/encephalitis.

METHODS

The authors examined the distribution of mortality rates of children in Japan aged <19 years with influenza during 1950-2000, influenza associated with central nervous system (CNS) signs in the period 1950-1978, and the estimated cases of influenza associated with acute encephalopathy/encephalitis in the period 1987-2000.

RESULTS

Total influenza mortality among children aged <19 years has increased since 1990, with children aged <4 years after 1994 being the worst affected. The mean values of mortality rates of influenza associated with central nervous system signs during 1963-1978 and the estimated mortality of children aged <9 years during 1979-1994 were significantly lower than in some years before 1962, and after 1995 (P < 0.05). The annual mortality rates of influenza-associated acute encephalopathy/encephalitis during 1995-2000 were significantly higher than the expected mortality of influenza associated with central nervous system signs in children aged <14 years (P < 0.05).

CONCLUSION

The results of the present study suggest that mass immunization of school-aged children reduced the mortality rate from influenza-associated acute encephalopathy/encephalitis in children less than 9 years of age.

Technical report: Reduction of the influenza burden in children

Epidemiologic studies have shown that children of all ages with certain chronic conditions, such as asthma, and otherwise healthy children younger than 24 months (6 through 23 months) are hospitalized for influenza and its complications at high rates similar to those experienced by the elderly. Annual influenza immunization is already recommended for all children 6 months and older with high-risk conditions. By contrast, influenza immunization has not been recommended for healthy young children. To protect children against the complications of influenza, increased efforts are needed to identify and recall high-risk children. In addition, immunization of children between 6 through 23 months of age and their close contacts is now encouraged to the extent feasible. Children younger than 6 months may be protected by immunization of their household contacts and out-of-home caregivers. The ultimate goal is universal immunization of children 6 to 24 months of age. Issues that need to be addressed before institution of routine immunization of healthy young children include education of physicians and parents about the morbidity caused by influenza, adequate vaccine supply, and appropriate reimbursement of practitioners for influenza immunization. This report contains a summary of the influenza virus, protective immunity, disease burden in children, diagnosis, vaccines, and antiviral agents.

Successful protection by amantadine hydrochloride against lethal encephalitis caused by a highly neurovirulent recombinant influenza A virus in mice

A mouse model system for a lethal encephalitis due to influenza has been established by stereotaxic microinjection with the recombinant R404BP strain of influenza A virus into the olfactory bulb of C57BL/6 mice. The virus infection spread selectively to neurons in nuclei of the broad areas of the brain parenchyma that have anatomical connections to the olfactory bulb, leading to apoptotic neurodegeneration. The inflammatory reaction at the extended stage of viral infection involved the vascular structures affected by induction of inducible nitric oxide synthase and protein nitration; those were related to the etiology of fatal brain edema. The intraperitoneal administration of amantadine inhibited the viral growth in the brain and saved mice from the lethal encephalitis. The severity of neuronal loss paralleled the time lag between the virus challenge and the start of amantadine treatment. Thus, early pharmacological intervention is essential to minimize neurological deficits due to influenza virus-induced neurodegeneration.

Encephalitis and encephalopathy associated with an influenza epidemic in Japan

During the winter of 1998-1999, there was an outbreak of encephalitis/encephalopathy in Japan that appeared to be associated with influenza. We conducted a national survey of the prevalence and clinical features of disease and the associated outcomes and prognostic factors related to this outbreak. A total of 202 cases were analyzed, of which 148 were diagnosed as influenza-associated encephalitis/encephalopathy on the basis of virologic analysis. Of the 148 cases studied, 130 (87.8%) were type A influenza and 17 were type B. Encephalitis/encephalopathy developed mainly in children age <5 years, either on the day that influenza signs appeared or on the next day. The major signs included altered consciousness or loss of consciousness, convulsions, cough, and vomiting. In many patients, multiple-organ failure developed, and rates of mortality (31.8%) and disability (27.7%) were high. Thrombocytopenia and severely elevated transaminase levels were factors associated with a poor prognosis. Thus, influenza-associated encephalitis/encephalopathy progressed rapidly and was associated with poor outcomes.

Influenza B infection associated with encephalitis: treatment with oseltamivir

Encephalitis associated with acute influenza infection is unusual in nonepidemic years. A case of a 10-year-old child with influenza B encephalitis and profound weakness who was treated with oseltamivir is presented. This case illustrates several of the unusual findings associated with influenza infections and the result of treatment of influenza B encephalitis with oseltamivir.

Study of influenza-associated encephalitis/encephalopathy in children during the 1997 to 2001 influenza seasons

The 1997 to 2001 influenza A epidemics in Japan were markedly neurovirulent, and many children died of influenza-associated encephalitis/encephalopathy. We studied 20 patients with influenza-associated encephalitis/encephalopathy during the last four influenza seasons. No patients had been previously inoculated with influenza vaccine. Antipyretics were used in 16 patients before the onset of encephalopathy. Although all patients were treated intensively, 5 patients died and 8 had neurologic sequelae. Patients with coagulopathy, hepatic dysfunction, and computed tomographic abnormalities had a poor prognosis. The plasma concentrations of inflammatory cytokines were variable. The neuroradiologic findings could be divided into four categories. These findings indicated that the pathogenesis of the brain damage induced by influenza infection was variable. Further investigation is necessary to determine whether insufficient influenza vaccination or the use of antipyretics is one of the reasons for these epidemics of encephalopathy in Japanese children.