Influenza B infection associated with encephalitis: treatment with oseltamivir

Influenza B infections in children: A review

Influenza B (IFB) virus belongs to the Orthomyxoviridae family and has two antigenically and genetically distinct lineages; B/Victoria/2/87-like (Victoria lineage) and B/Yamagata/16/88-like (Yamagata lineage). The illness caused by IFB differs from that caused by influenza A. Outbreaks of IFB occur worldwide and young children exposed to IFB are likely to have a higher disease severity compared with adults. IFB mostly causes mild to moderate respiratory illness in healthy children. However, the involvement of other systems, a severe disease especially in children with chronic medical conditions and immunosuppression, and rarely mortality, has been reported. Treatment with oseltamivir or zanamivir decreases the severity of illness and hospitalization. Due to the enormous health and economic impact of IFB, these strains are included in vaccines. IFB illness is less studied in children although its impact is substantial. In this review, the epidemiology, clinical manifestations, treatment, prognosis, and prevention of IFB illness in children are discussed.

Neurologic Complications in Children Hospitalized With Influenza Infections: Prevalence, Risk Factors and Impact on Disease Severity

BACKGROUND

Influenza infection is a common cause of respiratory disease and hospitalization in children. Neurologic manifestations of the infection have been increasingly reported and may have an impact on the severity of the disease. The aim of this study is to describe neurologic events in pediatric patients hospitalized with influenza and identify associated risk factors.

METHODS

Retrospective cohort study which included all hospitalized patients with microbiologic confirmation of influenza disease over 4 epidemic seasons, focusing on neurologic complications. Demographic, laboratory and clinical data, as well as past history, were recorded. Descriptive and analytic statistical study was performed using SPSS and R statistical software.

RESULTS

Two hundred forty-five patients were included. Median age was 21 months (interquartile range, 6-57) and 47.8% had a previous underlying condition. Oseltamivir was administered to 86% of patients, median hospitalization was 4 days (interquartile range, 3-6), and pediatric intensive care unit admission rate 8.9%. Twenty-nine patients (11.8%) developed neurologic events, febrile seizures being the most frequent, followed by nonfebrile seizures and encephalopathy. Status epilepticus occurred in 4 children, and 69.6% of seizures recurred. Patients with a previous underlying condition were at greater risk of developing a neurologic complication [odds ratio (OR), 4.55; confidence interval (CI), 95% 1.23-16.81). Male sex (OR, 3.21; CI 95%, 1.22-8.33), influenza B virus (OR, 2.82; CI 95%, 1.14-7.14) and neurologic events (OR, 3.34; CI 95%, 1.10-10.19) were found to be risk factors for pediatric intensive care unit admission.

CONCLUSIONS

A significant proportion of influenza-related hospitalized patients develop neurologic complications, especially seizures which may be prolonged or recurrent. Previous underlying conditions pose the greatest risk to neurologic events, which increase disease severity.

Neurological and muscular manifestations associated with influenza B infection in children

BACKGROUND

Influenza viruses have been associated with various neurological and muscular symptoms. The aim of this study was to evaluate the pediatric neurological and muscular manifestations of influenza B during a 5-month epidemic at a single center.

METHODS

We retrospectively reviewed the medical records of 355 pediatric patients with laboratory-confirmed influenza B infection.

RESULTS

Neurological and muscular symptoms were exhibited by 28 patients (7.9%). The mean age was 48.7 ± 25.2 months. The mean time between respiratory symptoms and neurological symptoms was 2.2 ± 1.5 days. The most common symptom was seizure (19/28, 67.9%), followed by myositis (5/28, 17.9%), increased intracerebral pressure (1/28, 3.6%), delirium (1/28, 3.6%), and severe headache (1/28, 3.6%). There was one severe case of meningitis with myocarditis (1/28, 3.6%). All seizures were febrile: 15 simple febrile seizures (78.9%), three complex febrile seizures (15.8%), and one febrile status epilepticus (5.3%). The mean age of nine patients with their first seizures was 37.9 ± 22.2 months, which was older than the typical age of onset for febrile seizure. All the patients, except one, were treated with oseltamivir. There were no deaths or chronic debilitating sequelae.

CONCLUSIONS

The neurological and muscular complications of influenza B infection in children are relatively mild, and febrile seizure is the most common. However, clinicians should be alert to the possibility of rare severe complications during influenza B outbreaks.

Therapeutics against influenza

Despite 75 years of research into prevention and treatment of influenza, the viruses that cause this disease continue to rank as some of the most important pathogens afflicting humans today. Progress in development of therapeutics for influenza has been slow for much of that time, but has accelerated in pace over the last two decades. Two classes of antiviral medications are used in humans at present, but each has limitations in scope and effectiveness of use. New strategies involving these licensed agents, including alternate forms of delivery and combination therapy with other drugs, are currently being explored. In addition, several novel antiviral compounds are in various clinical phases of development. Together with strategies designed to target the virus itself, new approaches to interrupt host–pathogen interactions or modulate detrimental aspects of the immune response have been proposed. Therapy for influenza will likely undergo substantial changes in the decades to come, evolving with our knowledge of pathogenesis as new approaches become viable and are validated clinically.

Pharmacologic considerations for oseltamivir disposition: focus on the neonate and young infant

Across much of the world, pandemic H1N1 infection has produced a significant healthcare crisis, reflected in significant morbidity and mortality. Statistics reveal that infection-associated deaths among individuals without pre-existing conditions (e.g. immunosuppression) are clustered in pregnant women and young infants. In developing countries where the availability of influenzae vaccine is limited, the only currently available pharmacologic counter-measure for H1N1 disease is oseltamivir, a neuraminidase inhibitor with excellent in vitro activity against the virus. This drug is available in oral solid and liquid formulations, has excellent peroral bioavailability in adults, and generally has a very favorable safety profile. Many observational studies indicate that oseltamivir treatment is associated with symptomatic improvement in pediatric patients with H1N1 infection and, therefore, is considered to represent a viable therapeutic option for use in children. However, the disposition of the ethyl ester prodrug and its active metabolite has not been well characterized in infants and children. Presently, data are available from only two published investigations and preliminary summary information from a recent presentation of an ongoing study. Given that recent in vitro data support the importance of a target exposure-response profile for the active metabolite of oseltamivir and that many processes known to modulate drug disposition have a developmental basis, understanding the potential impact of age on oseltamivir disposition becomes crucial in the development of age-appropriate dosing regimens for the drug. In this review, the impact of ontogeny on processes that are important in regulating the absorption, distribution, metabolism, and excretion of oseltamivir and its active metabolite are considered. Data from both animal and human investigations are presented in the context of defining how development might influence the dose-exposure relationship and, most importantly, the significant variability associated with it. In addition, the available pediatric pharmacokinetic data for oseltamivir and its active metabolite are summarized and current 'information gaps' deserving of future study are presented.

Adolescent with neuropsychiatric symptoms associated with novel influenza A (H1N1) virus infection

Neurologic complications have been described previously in association with seasonal influenza A or B viruses, but the frequency with which these occur with novel influenza A (H1N1) virus infection is unknown. We describe a case of an adolescent with a bizarre neuropsychiatric picture associated with novel influenza A (H1N1) virus infection.

Novel influenza A (H1N1) encephalitis in a 3-month-old infant

Seasonal influenza virus infection has been associated with a variety of neurologic complications. We report a case of novel influenza A (H1N1) encephalitis in an infant aged 3 months with an upper respiratory infection, who presented seizures. The infection was confirmed in nasopharyngeal aspirate and cerebrospinal fluid. Treatment with oseltamivir was started. He was discharged without any neurologic sequelae.

Oseltamivir in human avian influenza infection

Avian influenza A viruses continue to cause disease outbreaks in humans, and extrapulmonary infection is characteristic. In vitro studies demonstrate the activity of oseltamivir against avian viruses of the H5, H7 and H9 subtypes. In animal models of lethal infection, oseltamivir treatment and prophylaxis limit viral replication and improve survival. Outcomes are influenced by the virulence of the viral strain, dosage regimen and treatment delay; it is also critical for the compound to act systemically. Observational data on oseltamivir treatment in the early stages of disease suggest it is useful for improving survival in patients infected with H5 viruses, and drug-selected resistance has only rarely been reported. The WHO strongly recommends oseltamivir for the treatment of confirmed or suspected cases of human H5 infection and prophylaxis of those at high risk of infection. In addition to oral dosing, nasogastric administration appears to be a viable option for the management of severely ill patients, as is the use of higher doses and prolonged schedules. F. Hoffmann-La Roche Ltd, the manufacturer of oseltamivir, is developing a mathematical model to allow rapid prediction of appropriate dosage regimens for any future pandemic. Roche is also funding the Avian Influenza Registry, an online database that aims to collect information from clinicians worldwide on the course of avian influenza in humans.

The management of encephalitis: clinical practice guidelines by the Infectious Diseases Society of America

Guidelines for the diagnosis and treatment of patients with encephalitis were prepared by an Expert Panel of the Infectious Diseases Society of America. The guidelines are intended for use by health care providers who care for patients with encephalitis. The guideline includes data on the epidemiology, clinical features, diagnosis, and treatment of many viral, bacterial, fungal, protozoal, and helminthic etiologies of encephalitis and provides information on when specific etiologic agents should be considered in individual patients with encephalitis.

Low penetration of oseltamivir and its carboxylate into cerebrospinal fluid in healthy Japanese and Caucasian volunteers

Oseltamivir is a potent, well-tolerated antiviral for the treatment and prophylaxis of influenza. Although no relationship with treatment could be demonstrated, recent reports of abnormal behavior in young individuals with influenza who were receiving oseltamivir have generated renewed interest in the central nervous system (CNS) tolerability of oseltamivir. This single-center, open-label study explored the pharmacokinetics of oseltamivir and oseltamivir carboxylate (OC) in the plasma and cerebrospinal fluid (CSF) of healthy adult volunteers over a 24-hour interval to determine the CNS penetration of both these compounds. Four Japanese and four Caucasian males were enrolled in the study. Oseltamivir and OC concentrations in CSF were low (mean of observed maximum concentrations [C(max)], 2.4 ng/ml [oseltamivir] and 19.0 ng/ml [OC]) versus those in plasma (mean C(max), 115 ng/ml [oseltamivir] and 544 ng/ml [OC]), with corresponding C(max) CSF/plasma ratios of 2.1% (oseltamivir) and 3.5% (OC). Overall exposure to oseltamivir and OC in CSF was also comparatively low versus that in plasma (mean area under the concentration-time curve CSF/plasma ratio, 2.4% [oseltamivir] and 2.9% [OC]). No gross differences in the pharmacokinetics of oseltamivir or OC were observed between the Japanese and Caucasian subjects. Oseltamivir was well tolerated. This demonstrates that the CNS penetration of oseltamivir and OC is low in Japanese and Caucasian adults. Emerging data support the idea that oseltamivir and OC have limited potential to induce or exacerbate CNS adverse events in individuals with influenza. A disease- rather than drug-related effect appears likely.

Neurologic complications in children hospitalized with influenza: characteristics, incidence, and risk factors

OBJECTIVE

To determine the characteristics, incidence, and risk factors for influenza-related neurologic complications (INC).

STUDY DESIGN

A retrospective cohort study of INC in children hospitalized with laboratory-confirmed influenza infection (LCI) from June 2000 to May 2004 was conducted. Systematic chart review was performed to identify clinical characteristics and outcomes. A neighborhood cohort was constructed to estimate the incidence of INC. Logistic regression was used to identify independent risk factors for INC.

RESULTS

Of 842 patients with LCI, 72 patients had an INC: influenza-related encephalopathy (8), post-infectious influenza encephalopathy (2), seizures (56), and other (6). Febrile seizures were the most common type of seizures (27). No patient died from an INC. In our neighborhood cohort, the incidence of INC was 4 cases per 100,000 person-years. An age of 6 to 23 months (odds ratio [OR], 4.2; 95% CI, 1.4-12.5) or 2 to 4 years (OR, 6.3; 95% CI, 2.1-19.1) and an underlying neurologic or neuromuscular disease (OR, 5.6; 95% CI, 3.2-9.6) were independent risk factors for the development of INC.

CONCLUSION

Seizures are the most common neurologic complication experienced by children hospitalized with influenza. In the United States, encephalopathy is uncommon. Young children and patients with neurologic or neuromuscular disease are at increased risk for INC.

Antiviral therapy of influenza

Influenza viruses are a leading cause of morbidity and mortality worldwide despite the availability of an effective vaccine. The emergence of highly pathogenic avian influenza viruses in southeast Asia, which can infect and kill humans and for which there is no vaccine, has heightened the need to establish a supply of effective antivirals. Two effective classes of anti-influenza drugs are currently available, and many attractive targets exist for further development. This review presents the current status of antiviral therapy of, and highlights the challenges presented by, the threat of pandemic influenza.

Neurologic complications associated with influenza A in children during the 2003-2004 influenza season in Houston, Texas

OBJECTIVES

Our objectives were to (1) describe the clinical characteristics of and viruses isolated from patients who presented with neurologic symptoms associated with influenza A infection and were hospitalized at Texas Children's Hospital during October and November 2003 and (2) to raise awareness of the neurologic complications of influenza among US children.

METHODS

We reviewed the medical and laboratory records of all children who were hospitalized with neurologic symptoms and who also had evidence of influenza virus infection by rapid antigen testing or viral isolation.

RESULTS

Eight children aged 5 months to 9 years with neurologic complications associated with influenza A were identified. None of the children had received the influenza vaccine. Four presented with seizures, 3 with mental status changes, and 1 with mutism. All but 1 of the patients had influenza A viral antigen detected in nasal wash samples. Influenza A virus was isolated in culture from nasal wash specimens obtained from 6 of the patients; influenza A virus was also isolated from the cerebrospinal fluid of 1 of these patients. None of the patients had serum metabolic abnormalities or other cerebrospinal fluid abnormalities. Three of the patients had brain imaging abnormalities. Five of the patients were treated with antivirals. All 8 of the patients survived, 6 with complete recovery and 2 with sequelae (1 mild and 1 severe).

CONCLUSIONS

Neurologic symptoms and sequelae were associated with influenza A virus infection in children during the 2003-2004 influenza season in Houston, Texas. Influenza should be considered in the differential diagnosis in patients with seizures and mental status changes, especially if they present with respiratory symptoms or during an influenza outbreak.

[A case of Influenza virus encephalitis in south of France]

INTRODUCTION

Influenza virus outbreaks occur each year, in France, during autumn and winter. Influenza-associated acute encephalitis were reported during epidemics or pandemics. Sporadic cases are rarely identified probably because influenza virus is not searched among etiology of febrile encephalitis.

EXEGESIS

We report a case of influenza-associated encephalitis complicated by adrenal insufficiency in a young woman. Diagnosis was based on seroconversion of serum influenza virus A antibodies (complement fixation test). Follow up of the patient showed a total recovery.

CONCLUSION

Influenza must be searched for any febrile encephalitis occurring during winter. Reverse transcriptase polymerase chain reaction (RT-PCR) on cerebrospinal fluid should be assessed. It is not actually a routine technique and we do not know yet if it is accurate enough for diagnosis. So, it is important to identify influenza virus and obtain documentary evidence concerning neurological impairment. Nevertheless, a better understanding of pathogenesis and use of vaccination are needed to improve prognosis.

Influenza A virus-associated acute necrotizing encephalopathy in the United States

During the past several years, influenza-associated acute necrotizing encephalopathy has been well-recognized in Asia but has not yet been reported in the United States. We describe a 28-month-old patient who displayed the classical clinical features of acute necrotizing encephalopathy in association with a documented influenza A infection. This disease is characterized by fever, a rapid alteration in consciousness and seizures, with radiologic involvement of the bilateral thalami and cerebellum.

Amantadine penetration into cerebrospinal fluid of a child with influenza A encephalitis

The use of amantadine has been advocated as treatment for influenza A encephalitis despite limited information regarding cerebrospinal fluid concentrations and the pathogenesis of encephalitis associated with influenza virus infections. We report a 2-year-old child with influenza A encephalitis treated with amantadine who achieved a potentially therapeutic concentration in cerebrospinal fluid. Despite this the child developed significant neurologic impairment.

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.

Encephalitis associated with influenza B virus infection in 2 children and a review of the literature

Two children with influenza B-associated encephalitis (IBAE) presented to our hospital during the winter of 2000-2001, both of whom had cases notable for mutism in association with encephalitis. A review of the literature identified 13 additional reports consistent with IBAE that contained sufficient data for analysis. Eleven of 15 reported cases occurred in children aged <or=18 years; of these, more than one-half occurred in children <11 years of age. Neurologic symptoms appeared within the first 4 days of illness in 13 cases. Speech abnormalities were observed in 4 patients and consisted of mutism in 3. Although the majority of patients recovered fully, 3 were left with neurologic sequelae, and 1 died. These cases reveal the spectrum of IBAE and its potential for long-term sequelae. Clinicians caring for children should remain vigilant for this rare complication of influenza B virus infection.

Viral meningitis and encephalitis: traditional and emerging viral agents

In the United States, the annual number of central nervous system (CNS) infections that occur as a result of viral agents far exceeds that of infections caused by bacteria, yeast, molds, and protozoa combined. The recent incursion of West Nile virus (WNV) into North America has led to a dramatic change in the incidence and epidemiology of summer-associated viral CNS disease. As a result of increased testing for WNV, lesser known viral causes of CNS infection have been identified. Even the epidemiology of such traditional viral neuropathogens as rabies has changed in recent years. This review provides an overview of viruses traditionally associated with meningitis and encephalitis (enteroviruses, La Crosse virus, St. Louis encephalitis virus, eastern and western equine viruses, varicella-zoster virus), as well as several of the less common (Powassan virus, lymphocytic choriomeningitis virus, Colorado tick fever virus, rabies virus, influenza viruses, etc.) and emerging (West Nile virus) viral pathogens.

Influenza A and B virus infections in children

To obtain data on the clinical manifestations of infection, the age distribution, and the underlying conditions of children with influenza severe enough to lead to hospital referral, we performed a retrospective study of children treated at Turku University Hospital (Turku, Finland) in 1980-1999. Influenza A or B antigen was detected in the nasopharyngeal aspirates of 683 of the 15,420 children studied. The median age of children with influenza A was 2.0 years (n=544), and that of children with influenza B was 4.2 years (n=139) (P<.001). One-fourth of the children had an underlying medical condition. High fever, cough, and rhinorrhea were the most frequently recorded symptoms. Acute otitis media developed in 24% of the children, and pneumonia developed in 9% of the children. The study shows that the majority of patient hospitalizations for pediatric influenza involve previously healthy infants and young children. Laboratory confirmation of influenza is particularly important for children because the clinical presentation of the infection is less characteristic than that seen in adults.

Influenza diagnosis and treatment in children: a review of studies on clinically useful tests and antiviral treatment for influenza

BACKGROUND

Prompt testing for influenza can help guide clinical management of patients with suspected influenza. Three antiviral medications, amantadine, oseltamivir and zanamivir, are approved for treatment of influenza in children. Rimantadine and ribavirin have also been used.

OBJECTIVES

To review the published evidence on clinically useful diagnostic tests and antiviral treatment for influenza virus infections in children.

METHODS

Studies published from 1966 through September 2002 were reviewed on clinical diagnosis, immunofluorescence and rapid influenza tests and on antiviral treatment of influenza virus infections among pediatric populations.

RESULTS

No studies assessed the accuracy of clinical diagnosis of influenza in children compared with viral culture. Compared with viral culture, direct immunofluorescence antibody and indirect immunofluorescence antibody tests for influenza had fair to moderate median sensitivities and high median specificities, whereas rapid influenza diagnostic tests had moderate median sensitivities and moderately high median specificities. No randomized, placebo-controlled studies were found of amantadine or rimantadine for treatment of influenza A. In a few separate controlled studies, oseltamivir, zanamivir and ribavirin each reduced symptom duration of influenza compared with placebo.

CONCLUSIONS

Additional data are needed about the accuracy of clinical diagnosis of influenza in children. Although direct immunofluorescence antibody staining, indirect immunofluorescence antibody staining and rapid tests are moderately to reasonably accurate in detecting influenza virus infections in children, physicians should use clinical judgment and local surveillance data about circulating influenza viruses when interpreting test results. Further controlled studies of the efficacy, adverse effects and emergence of antiviral resistance during treatment of influenza are needed for all of the antiviral drugs.