Respiratory syncytial viral infection in infants with congenital heart disease

Serious and lethal respiratory tract infections of viral etiology in children

Viruses may lead to serious and lethal pulmonary infections in immunocompetent and immunocompromised children. Series of children with acute respiratory distress syndrome and series of children requiring extracorporeal membrane oxygenation, as well as reported series of nosocomial viral illness, offer an insight into the extent of serious viral disease documented in the medical literature. Series of children with specific viral respiratory illness also will be reviewed, as will the means of diagnosis in these groups of patients. Copyright © 2000 by W.B. Saunders Company

Respiratory syncytial virus pneumonitis in immunocompromised adults: clinical features and outcome

BACKGROUND

Though predominantly an infection of children, respiratory syncytial virus (RSV) also infects adults, particularly those with immune compromise.

OBJECTIVES

To define the clinical spectrum and impact of RSV pneumonitis on hospitalized, immunocompromised adults.

METHODS

Retrospective chart review. Clinical parameters including premorbid conditions, presentation, radiologic findings, treatment and outcome were examined in a consecutive patients series from an inpatient tertiary-care center. Eleven immunocompromised adults who had undergone bronchoalveolar lavage (BAL) between January 1987 and December 1996 and who had culture-verified RSV pneumonitis were evaluated.

RESULTS

This series consisted primarily of patients undergoing chemotherapy or bone marrow transplantation for lymphoma or leukemia. Two were immunosuppressed due to high-dose corticosteroids. A majority (91%) were admitted between November and May, with dyspnea and productive cough. In contrast to earlier studies, there was a paucity of upper respiratory infection symptoms (i.e. sinus congestion, sore throat) and a preponderance of lower respiratory physical exam findings (i.e. wheezing, bibasilar rales). Patients were typically hypoxemic and febrile prior to BAL. Eight demonstrated co-isolates of bacterial or fungi on BAL. The chest radiographs generally revealed diffuse patchy infiltrates, including alveolar opacities. Histology demonstrated diffuse alveolar damage, bronchiolitis with organizing pneumonia, and hyaline membrane formation. Over half required intubation, and 55% died. Although ribavirin therapy may be beneficial in some intubated patients, its overall efficacy cannot be established from this series.

CONCLUSION

RSV is a serious cause of morbidity and mortality in immunocompromised adults. Further development and implementation of an effective vaccine and additional therapeutic interventions are needed.

Safety and efficacy of palivizumab prophylaxis in children with congenital heart disease

BACKGROUND

Infants with congenital heart diseases (CHD) are at high risk for Respiratory syncytial virus (RSV) infection, which causes severe respiratory distress. Palivizumab, an anti-RSV monoclonal antibody, was licensed in the USA, Europe and Canada, and a large-scale placebo-controlled double-blind test in these countries confirmed its efficacy and safety. A survey using questionnaires to assess usage, prophylactic efficacy, and safety of palivizumab in Japanese infants and young children with CHD was conducted.

METHODS

The survey was conducted between October 2002 and March 2003. The questionnaire asked for patients' characteristics, presence of CHD, underlying diseases, starting date and number of injection, adverse events, correlation between adverse events and treatment with palivizumab, and evaluation of efficacy.

RESULTS

In total, 108 infants were reported from 61 institutions. A total of 60 of the 108 infants evaluated without major non-cardiac complications received intramuscular injection of 15 mg/kg per month of palivizumab in a manner not consistent with approved indications for this drug. A total of 43 cases (39.8%) had complexed CHD, while 64 cases (59.3%) had the first injection in October or November. The average number of injections was 3.0 +/- 1.4. Seven children (6.5%) had notable respiratory infections confirmed by positive test for RSV antigen, and five (4.6%) were hospitalized. No children died nor received mechanical ventilation. The number of adverse events was nine in five cases. There was no significant relationship between adverse events and treatment with palivizumab.

CONCLUSION

Palivizumab is well-tolerated, fairly effective and safe in preventing severe RSV infection in infants and young children with CHD.

Fatal coronary artery anomaly presenting as bronchiolitis

During winter outbreaks of respiratory syncytial virus bronchiolitis from 2002 to 2004, three infants presented with a presumptive diagnosis of lower respiratory tract infection and wheezing. The clinical condition in two cases was rapidly progressive and precipitated into intractable shock; clinical and instrumental examinations revealed a cardiac origin of their illness. A subacute presentation permitted a cardiological assessment and a proper treatment in the third infant. An abnormal origin of the left coronary artery from the pulmonary trunk was demonstrated in all cases. The concurrent acute airway infection had a catastrophic effect on the underlying cardiovascular anomaly leading to refractory cardiogenic shock and death.

CONCLUSION

Admission chest X-ray film and arterial gas analysis can raise the suspicion of cardiac involvement when treating a severe wheezing episode in young infants. Paediatric cardiological evaluation with two-dimensional echocardiography may eventually reveal this rare condition, whereas cardiac catheterisation with aortography remains the standard means of diagnosis.

Respiratory syncytial virus influences NF-kappaB-dependent gene expression through a novel pathway involving MAP3K14/NIK expression and nuclear complex formation with NF-kappaB2

A member of the Paramyxoviridae family of RNA viruses, respiratory syncytial virus (RSV), is a leading cause of epidemic respiratory tract infection in children. In children, RSV primarily replicates in the airway mucosa, a process that alters epithelial cell chemokine expression, thereby inducing airway inflammation. We investigated the role of the mitogen-activated protein kinase kinase kinase 14/NF-kappaB-inducing kinase (NIK) in the activation of NF-kappaB-dependent genes in alveolus-like A549 cells. RSV infection induces a time dependent increase of NIK mRNA and protein expression that peaks 12 to 24 h after viral exposure. Immunoprecipitation kinase assays indicate that NIK kinase activity is activated even more rapidly (within 6 h of RSV adsorption) associated with an endogenous approximately 50-kDa NF-kappaB2 substrate. Because NIK associates with IKKalpha to mediate processing of the 100-kDa NF-kappaB2 precursor into its 52-kDa DNA binding isoform ("p52"), the effects of RSV on NIK complex formation with IKKalpha and NF-kappaB2 were determined by coimmunoprecipitation assay. We find that NIK, IKKalpha, and both 100 kDa- and 52-kDa NF-kappaB2 isoforms strongly complex 15 h after exposure to RSV at times subsequent to NIK kinase activation. Western immunoblot and microaffinity DNA pull-down assays showed a parallel increase in nuclear translocation and DNA binding of the NF-kappaB2-Rel B complex. Interestingly, we make the novel observations that NIK also transiently translocates into the nucleus complexed with 52-kDa NF-kappaB2. Small interfering RNA-mediated NIK "knock-down" blocked RSV-inducible 52-kDa NF-kappaB2 processing and interfered with the early activation of a subset of NF-kappaB-dependent genes, indicating the importance of this activation pathway in the genomic NF-kappaB response to RSV. Together, these data indicate that RSV infection rapidly activates the noncanonical NF-kappaB activation pathway prior to the more potent canonical pathway activation. This appears to be through a novel mechanism involving induction of NIK kinase activity, expression, and nuclear translocation of a ternary complex with IKKalpha and processed NF-kappaB2.

The potential impact of prophylaxis against bronchiolitis due to the respiratory syncytial virus in children with congenital cardiac malformations

AIMS

To determine the number of infants in the Mersey and North West regions with congenital cardiac disease for whom palivizumab may be appropriate, and to examine the potential impact of introducing prophylaxis with palivizumab on these patients and their economic management.

METHODS

We identified those infants deemed to be at high risk, matching the population recently studied by the Cardiac Synagis Group, from the database of the cardiology department of the hospital. The number of patients under the care of the paediatric cardiologists admitted to Alder Hey Hospital with respiratory syncytial viral bronchiolitis over the last three seasons was identified from hospital coding records, and the database of the cardiology department.

RESULTS

There are 131 patients at high risk each year. Of these, over the last three "bronchiolitis seasons", 39 infants have been admitted to the hospital with bronchiolitis due to the respiratory syncytial virus. This represents a hospitalisation rate of 10 per cent, as was seen in the study of the Cardiac Synagis Group. Using a monthly dose of 15 milligrams per kilogram for five doses, the cost per patient is 2,650 pounds sterling for the season. To treat the 131 patients seen at Alder Hey, therefore, would cost 346,800 pounds each year. Applying the reductions in hospitalisation identified in the study by the Cardiac Synagis Group to our population would produce an expected reduction in patients hospitalised from 13 to 7 per year, reducing the total length of stay in our hospital wards from 169 to 76 days, and in the paediatric intensive care unit from 93 to 21 days. This amounts to a potential saving of 190,800 pounds per year. Reducing transfers to more distant paediatric intensive care units for referrals refused because of lack of beds could save an additional 50,000 pounds.

DISCUSSION

We estimate the net cost of introducing palivizumab for this population to be 106,000 pounds per year. There would, of course, be additional costs involved in setting up this service, as well as additional savings and benefits. This cost is comparable with other new biologic therapies now routinely used in the United Kingdom, such as etanercept for juvenile arthritis. There are, currently, no other obvious therapies that have the potential to reduce admissions to hospital and intensive care during the winter months, when beds are at their most scarce.

The impact of severe respiratory syncytial virus on the child, caregiver, and family during hospitalization and recovery

OBJECTIVE

To quantify the magnitude of child, caregiver, and family distress associated with hospitalization for severe respiratory syncytial virus (RSV) and the posthospitalization recovery period.

DESIGN

A prospective study of 46 RSV-hospitalized infants and children < or =30 months of age with a history of prematurity (gestational age of < or =35 weeks) and 45 age-matched control subjects was performed. RSV group data were gathered during hospitalization and on days 4, 14, 21, and 60 after discharge; control group data were collected at the end of the RSV season and 60 days thereafter.

MAIN OUTCOME MEASURES

RSV severity; caregiver's rating of the child's health (100-point rating) and functional status (Functional Status IIR); caregiver health, stress (7-point rating), and anxiety (Spielberger State Anxiety Inventory); and family health and functioning (Family Adaptability and Cohesion Evaluation Scale II) were recorded.

RESULTS

The mean age of the sample was 10.2 months; 51% of the subjects were male. The average duration of hospital stay for the RSV group was 5.8 +/- 8 days. Most patients received supplemental oxygen (76%) and were monitored for apnea (60%). The mean age of the caregivers (93% mothers) was 29 years. During hospitalization, the RSV-infected patients' health and functional status were significantly poorer than those of control subjects. Caregivers of RSV-infected children reported more stress, greater anxiety, poorer health, and poorer family health and functioning. As long as 60 days after discharge, caregivers of RSV-infected children reported the children's health as significantly poorer and were personally more anxious, compared with control subjects.

CONCLUSIONS

RSV-related hospitalization creates significant distress for infants and children, caregivers, and families, with some effects extending as long as 60 days after discharge.

The European Forum for Clinical Management: prophylaxis against the respiratory syncytial virus in infants and young children with congenital cardiac disease

A recent, randomised, double-blind, placebo-controlled trial has demonstrated the effectiveness of palivizumab (Synagis) for prophylaxis against infection by the respiratory syncytial virus in 1,287 young children with congenital cardiac disease. Guidelines for the use of palivizumab in these children considered to be at high risk were published by the American Academy of Pediatrics, followed by similar guidelines from the British Paediatric Cardiac Association, and recommendations from a number of other individual countries, including Canada, Germany, Spain, and France. In May, 2004, further discussion was held between a group of 15 paediatric cardiologists at a European forum for clinical management held in Munich, Germany. The objective of this forum was to define optimal recommendations on prevention of infection by the respiratory syncytial virus in infants and young children with congenital cardiac disease, appropriate to the clinical needs and style of those practising in paediatrics in individual countries. Participants were invited because of their knowledge of the therapeutic area, and for their experience of using palivizumab for prophylaxis against the respiratory syncytial virus in children with congenitally malformed hearts. Measures to educate the carers of children with such congenital malformations on precautions against infection by the respiratory syncytial virus were discussed, along with the many different aspects of best practice for therapeutic prophylaxis with palivizumab. The most appropriate timing of prophylaxis, recommendations for which children are most likely to benefit from prophylaxis, and suggested protocols were among the issues covered. The recommendations resulting from the discussions are presented in this paper, as a step towards reaching consensus.

Infection by the respiratory syncytial virus in infants and young children at high risk

The respiratory syncytial virus is the most common cause of infection of the lower respiratory tract in infants and young children, and is the leading cause of hospitalisation and death due to viral illness during the first year of life. In otherwise healthy infants, the virus usually causes only mild respiratory illness, but premature babies and infants with chronic lung disease, those with congenitally malformed hearts, or those who are immunodeficient, are at increased risk of serious illness, hospitalisation, and death. Recent infection with the virus is also associated with increased postoperative complications after corrective surgery for congenitally malformed hearts. No effective vaccine is currently available, and treatment is limited to supportive therapy. Prevention in groups deemed to be at high-risk, therefore, is essential. In addition to measures for control of infection, prophylactic immunotherapy is indicated in selected patients. Palivizumab (Synagis) is a monoclonal antibody indicated for the prevention of serious viral disease of the lower respiratory tract in premature infants, those with chronic lung disease, and those with haemodynamically significant congenital cardiac lesions. Palivizumab is given intramuscularly, usually as a monthly injection during the so-called "season". In a recent international, randomised, double-blind, placebo-controlled trial in 1,287 children less than or equal to 2 years old with haemodynamically significant congenital cardiac malformations, prophylaxis achieved a relative reduction of 45 per cent in the incidence of antigen-confirmed viral-related hospitalisation, and reduced the duration of hospital stay by 56 per cent. National and international guidelines, therefore, now recommend routine prophylaxis in the first year of life in children with haemodynamically significant congenital cardiac disease.

Administration of the first dose of palivizumab immunoprophylaxis against respiratory syncytial virus in infants before hospital discharge: what is the evidence for its benefit?

BACKGROUND

Palivizumab is 1 of 2 agents used to prevent severe lower respiratory tract disease due to respiratory syncytial virus (RSV) infection. The American Academy of Pediatrics and the American College of Obstetricians and Gynecologists recommend administering the first dose of RSV immunoprophylaxis to eligible infants before hospital discharge. Unfortunately, third-party payers frequently do not separately reimburse administration of this therapy to hospitalized infants.

OBJECTIVE

Because palivizumab is commonly used to provide RSV immunoprophylaxis, we systematically reviewed all published data on this drug to determine whether the evidence supports the recommendation of administering the first dose before hospital discharge.

METHODS

MEDLINE was searched for all articles published in English from January 1, 1996, to October 31, 2003, using the search terms palivizumab and Synagis, and the following data were extracted onto a standardized form: author(s), year of publication, study design, patient population, sample size, criteria used for administration of RSV prophylaxis, location of palivizumab prophylaxis (inpatient or outpatient), parental satisfaction with administration of prophylaxis, incidence of RSV infection, and hospitalization rates for RSV. All selected publications were reviewed to determine whether they reported differences in the incidence of RSV infection or hospitalization in patients who received palivizumab before discharge compared with those who received it after discharge. Only those publications that specifically documented administration of the first dose of palivizumab before hospital discharge were included in the final analysis.

RESULTS

Six of the 166 studies reviewed met the selection criteria. Although all 6 studies reported reduced RSV hospitalization rates with palivizumab prophylaxis, no study directly compared inpatient and outpatient administration with regard to parental satisfaction or rates of RSV infection or hospitalization. Furthermore, based on the data in these studies, it was not possible to detect any differences in parental satisfaction or rates of RSV infection or hospitalization between the 2 locations of administration.

CONCLUSIONS

Based on our literature review, there is no evidence to support the recommendation that palivizumab be administered before hospital discharge in every infant who meets the criteria for RSV immunoprophylaxis. Eligible infants may be given the initial dose of RSV prophylaxis as outpatients, reducing the cost to institutions that currently provide palivizumab before hospital discharge.

Development, implementation, and evaluation of a community- and hospital-based respiratory syncytial virus prophylaxis program

PURPOSE

To implement and deliver a respiratory syncytial virus prophylaxis (RSVP) program in response to the Canadian Pediatric Society recommendations.

METHODS

A novel program was designed to provide inpatient RSVP for at-risk infants cared for in 1 tertiary care newborn intensive care unit (NICU). This inpatient program was part of a coordinated approach to RSVP, designed and implemented by 3 hospitals. An RSVP program logic model was created and used by a multidisciplinary team to evaluate the in-house program and identify areas of program activity requiring improvement.

RESULTS

Following the 2000 to 2001 RSV season, a compliance and outcomes audit was performed in the tertiary center; 193 infants were enrolled in the RSVP program and 162 infants had received RSVP in the NICU [Mean = 1.64 doses]. Telephone follow-up with the parents of discharged infants identified that 159 infants (98%) had successfully completed their full course of RSVP. Using the RSVP program logic model, 5 areas for program improvement were identified including infant recruitment, patient transfer/discharge processes, product procurement, preparation/distribution/administration of doses, and healthcare team communication.

CONCLUSIONS

Interdisciplinary collaboration is an important factor in the success of the RSVP program and has supported a consistent model of care for the delivery of RSVP. The program logic model provided a useful structure to systematically review the RSVP program in this organization.

Economic analysis of palivizumab in infants with congenital heart disease

OBJECTIVE

Palivizumab has been shown to reduce the number of respiratory syncytial virus (RSV)-related hospitalizations by 45% in children with congenital heart disease (CHD). The American Academy of Pediatrics has recommended that infants with hemodynamically significant CHD be considered for palivizumab. However, the economic implications of palivizumab prophylaxis in the CHD population have not been evaluated. In the present study, we sought to examine the cost savings and cost utility of RSV prophylaxis with palivizumab in children with CHD.

METHODS

Probabilities of hospitalization and efficacy of prophylaxis were based on published results. Costs of hospitalization were derived from a published analysis of bronchiolitis hospitalization costs from a consortium of children's hospitals. A hypothetical cohort of 10,000 CHD patients (half of whom would receive palivizumab) was created to calculate cost-savings and cost-utility. To assess cost utility, we assumed that by reducing hospitalization, palivizumab would reduce RSV-related hospital mortality, generally reported to be 3% in CHD patients. Sensitivity analysis was performed.

RESULTS

On the basis of a protocol of 5 monthly doses of palivizumab, the cost of prophylaxis for 1 RSV season was calculated as 6160 dollars per patient. After accounting for impact on direct and indirect costs of hospitalization, administration of palivizumab to 5000 CHD patients would result in a net loss of 20,415,753 dollars. If one assumes that palivizumab confers a survival benefit, then the cost of life-year saved is 100,338 dollars and cost of quality-adjusted life-year saved is 114,337 dollars.

CONCLUSIONS

The cost of palivizumab prophylaxis was high relative to benefits realized. Given the large number of CHD patients who might be considered candidates for RSV prophylaxis (>6000 patients per year in United States) routine use of palivizumab in young children with hemodynamically significant CHD needs to be evaluated further.

Nuclear heat shock response and novel nuclear domain 10 reorganization in respiratory syncytial virus-infected a549 cells identified by high-resolution two-dimensional gel electrophoresis

The pneumovirus respiratory syncytial virus (RSV) is a leading cause of epidemic respiratory tract infection. Upon entry, RSV replicates in the epithelial cytoplasm, initiating compensatory changes in cellular gene expression. In this study, we have investigated RSV-induced changes in the nuclear proteome of A549 alveolar type II-like epithelial cells by high-resolution two-dimensional gel electrophoresis (2DE). Replicate 2D gels from uninfected and RSV-infected nuclei were compared for changes in protein expression. We identified 24 different proteins by peptide mass fingerprinting after matrix-assisted laser desorption ionization-time of flight mass spectrometry (MS), whose average normalized spot intensity was statistically significant and differed by +/-2-fold. Notable among the proteins identified were the cytoskeletal cytokeratins, RNA helicases, oxidant-antioxidant enzymes, the TAR DNA binding protein (a protein that associates with nuclear domain 10 [ND10] structures), and heat shock protein 70- and 60-kDa isoforms (Hsp70 and Hsp60, respectively). The identification of Hsp70 was also validated by liquid chromatography quadropole-TOF tandem MS (LC-MS/MS). Separate experiments using immunofluorescence microscopy revealed that RSV induced cytoplasmic Hsp70 aggregation and nuclear accumulation. Data mining of a genomic database showed that RSV replication induced coordinate changes in Hsp family proteins, including the 70, 70-2, 90, 40, and 40-3 isoforms. Because the TAR DNA binding protein associates with ND10s, we examined the effect of RSV infection on ND10 organization. RSV induced a striking dissolution of ND10 structures with redistribution of the component promyelocytic leukemia (PML) and speckled 100-kDa (Sp100) proteins into the cytoplasm, as well as inducing their synthesis. Our findings suggest that cytoplasmic RSV replication induces a nuclear heat shock response, causes ND10 disruption, and redistributes PML and Sp100 to the cytoplasm. Thus, a high-resolution proteomics approach, combined with immunofluorescence localization and coupled with genomic response data, yielded unexpected novel insights into compensatory nuclear responses to RSV infection.

RSV outbreak in a paediatric intensive care unit

The Royal Liverpool Children's Hospital-Alder Hey paediatric intensive care unit (PICU) usually has a low rate of nosocomial respiratory syncytial virus (RSV) infection. We report and analyse a major outbreak of nosocomial (acquired) RSV infection on the PICU during a RSV season. All children admitted to the PICU were studied during the six-month winter period 1 October 2002 to 31 March 2002. Nasopharyngeal aspirates were tested using an in vitro enzyme-linked immunoassay (ELISA) membrane test for RSV antigen. PICU-acquired RSV infection was considered to have occurred when a child admitted to the PICU was RSV negative, or from whom no samples were taken as they did not exhibit signs of bronchiolitis, but was RSV positive five or more days after the admission. Fifty-four patients tested RSV positive using the ELISA on the PICU. All the patients were ventilated. Thirty-nine children were RSV positive using the ELISA on admission to the PICU ('imported' cases) and 15 became RSV positive whilst on the PICU ('acquired' cases). The source of the acquired RSV infection accounting for the first peak/outbreak in nosocomial cases were RSV-positive children in isolation cubicles. Acquired cases of RSV infection subsided with reinforcement of traditional methods of barrier precautions. The source of the second peak in nosocomial cases were persistent shedders of RSV. Seventy-three percent (11/15) of the acquired RSV cases had one or more of the following co-morbidities: congenital heart disease, chronic lung disease, airways abnormalities or immunosuppression. Droplet precautions (strict handwashing, use of gloves if handling body fluids, single-use aprons, education) rather than the physical barrier of the cubicle itself played a more important role in curtailing nosocomial spread. Persistent shedders of RSV are an important potential source of nosocomial RSV infection within a PICU. Patients with co-morbidities are at increased risk of nosocomial RSV infection.

Low incidence of respiratory syncytial virus hospitalisations in haemodynamically significant congenital heart disease

BACKGROUND

Haemodynamically significant congenital heart disease (CHD) is a risk factor for severe respiratory syncytial virus (RSV) disease in young children. Population based data on the incidence of RSV hospitalisations in CHD patients are needed to estimate the potential usefulness of RSV immunoprophylaxis using palivizumab.

AIMS

(1) To obtain population based RSV hospitalisation rates in children <24 months of age with CHD. (2) To compare these rates with non-CHD patients and with previous studies. (3) To determine the number of patients needed to treat (NNT) with palivizumab to prevent one RSV hospitalisation.

METHODS

Six year, longitudinal, population based study at an institution, which is the sole provider of primary to tertiary in-patient care for a precisely defined paediatric population.

RESULTS

RSV hospitalisation rates (per 100 child-years) in CHD patients aged <6, <12, 12-24, and <24 months of age were 2.5 (95% CI 0.8 to 5.6), 2.0 (0.8 to 3.8), 0.5 (0.1 to 1.8), and 1.3 (0.6 to 2.3), respectively, and the relative risk (RR) in comparison with non-CHD patients was 1.4 (0.6 to 3.1), 1.6 (0.8 to 3.2), 2.7 (0.7 to 9.7), and 1.8 (1.0 to 3.3), respectively. NNT was between 80 (35 to 245) and 259 (72 to 2140) for various age groups.

CONCLUSION

RSV hospitalisation rates in CHD patients were fourfold lower than reported from the USA. Based on these low rates and RR, unrestricted use of palivizumab does not appear to be justified in this study area.

Use of palivizumab to control an outbreak of syncytial respiratory virus in a neonatal intensive care unit

To evaluate the safety and effectiveness of a humanized respiratory syncytial virus (RSV) monoclonal antibody (palivizumab) to control an outbreak of RSV in a neonatal intensive care unit (NICU), we retrospectively analysed two RSV outbreaks. Between 11 November 1998 and 18 March 1999, two separate RSV outbreaks occurred in a large (26 beds) NICU. All procedures for preventing nosocomial spread of RSV (including the use of palivizumab in the second outbreak) were retrospectively analysed. The cumulative incidence (CI), secondary attack rate (SAR) and risk ratio of infection were determined before and after the use of palivizumab for all patients and for those with gestational age below and above 32 weeks in the NICU during the second outbreak. Standard infection control measures were effective in the first outbreak (three cases). In the second outbreak, after three index cases, five additional infants were newly RSV-infected within one month. Three infants had RSV pneumonia and required mechanical ventilation; one infant died. Standard infection control procedures were initiated from the beginning of this outbreak. Palivizumab was given to all infants in the NICU after the fifth case was identified. CI was 2.4% in the first 15 days and 10.5% in the second, and SAR was 2.9 per thousand in the first 15 days and 14.1 per thousand in the second, both dropping to zero after the administration of palivizumab. The risk ratio of infection was 4.65 times higher in infants under 32 weeks gestational age. After the use of palivizumab, there were no additional identified cases. In addition to careful infection control procedures, the use of palivizumab might have contributed to arresting the outbreak of RSV infection in the NICU, suggesting that it could be an additional resource in the control of severe nosocomial RSV outbreaks.

Bacteraemia and antibiotic use in respiratory syncytial virus infections

AIMS

To examine the frequency of and risk factors for bacteraemia in children hospitalised with respiratory syncytial virus (RSV) infection; and to determine current use of antibiotics in hospitalised children with RSV infection.

METHODS

Retrospective study of all children, aged 0-14 years, admitted to a tertiary children's hospital with proven RSV infection over a four year period. Children with concurrent bacteraemia and RSV infection were identified, and risk factors examined for bacteraemia. The case notes of a randomly selected comparison sample of 100 of these RSV infected children were examined to assess antibiotic use and population incidence of risk factors for severe RSV infection.

RESULTS

A total of 1795 children had proven RSV infection, and blood cultures were sent on 861 (48%). Eleven (0.6%) of the 1795 RSV positive children had bacteraemia. RSV positive children had a significantly higher incidence of bacteraemia if they had nosocomial RSV infection (6.5%), cyanotic congenital heart disease (6.6%), or were admitted to the paediatric intensive care unit (2.9%). Forty five (45%) of the random comparison sample of RSV infected children received antibiotics.

CONCLUSIONS

Bacteraemia is rare in RSV infection. Children with RSV infection are more likely to be bacteraemic, however, if they have nosocomial RSV infection, cyanotic congenital heart disease, or require intensive care unit admission.

Role of serum neutralizing antibody in reinfection of respiratory syncytial virus

BACKGROUND

To clarify the role of serum antibody in respiratory syncytial virus (RSV) reinfection, the authors conducted a follow-up study of patients with primary RSV infection.

METHODS

From 1994 to 1995, 256 patients were a diagnosed with primary RSV infection based on the antigen detection in nasopharyngeal secretions using enzyme linked immunoassay method. One hundred and sixty-five patients were followed-up for 1 year, and 87 of the 165 patients showed respiratory symptoms in winter. When a patient had a symptom such as cough, wheezing, rhinorrhea or fever, the nasopharyngial secretion was examined for the presence of RSV. Forty-one patients (group 1) were diagnosed with reinfection with RSV and the other 46 patients (group 2) were not diagnosed with reinfection. The authors compared clinical features between primary infection and reinfection of group 1 and serum neutralization test (NT) antibody titers to RSV between group 1 and 2.

RESULTS

The mean age was 6.0 +/- 3.6 months at RSV primary infection and 14.6 +/- 8.2 months at RSV reinfection. Hospitalization, oxygen supplementation, and use of respirator were required by 71%, 39%, 2%, respectively, in primary infection, and by 22%, 0%, 0%, respectively, in reinfection. All children in group 1 had titers of 1 : 16 or lower, while 39.1% of children in group 2 had titers of 1 : 16 or lower (P < 0.05). No patient with the titers of 1 : 32 or higher had symptomatic reinfection. Serum NT antibodies to RSV of outpatients were higher than those of inpatients at reinfection.

CONCLUSIONS

The severity of illness in RSV reinfection is generally milder than that in primary infection. Our findings suggest that NT antibodies play an important role in reducing the severity of illness as well as in protection from RSV reinfection.

Physiologic risk factors for respiratory viral infections and immunoprophylaxis for respiratory syncytial virus in young children with congenital heart disease

BACKGROUND

Infants and children with congenital heart disease (CHD) are a population at increased risk for infection with respiratory syncytial virus (RSV) and its inherent complications compared with the general population. RSV infection increases morbidity from respiratory complications in young CHD patients.

METHODS

In an effort to guide strategies for reducing RSV-associated risk in patients with CHD, predisposing factors for severe RSV as well as experimental approaches for prevention were reviewed.

CONCLUSIONS

Risk factors that may exacerbate the adverse effects of respiratory disease in young CHD patients include compromised cardiorespiratory status at baseline, altered pulmonary mechanics, potential cyanosis and/or pulmonary hypertension and ventilation-perfusion mismatch. Furthermore patients with such conditions are at increased risk from RSV lower respiratory tract infection, making RSV prevention in patients with CHD an important goal. Because the efficacy and safety of active immunization for RSV have not yet been established, a number of approaches toward passive immunoprophylaxis have been investigated. Monthly prophylaxis with palivizumab, a humanized murine monoclonal anti-F glycoprotein antibody preparation, reduced the rate of hospitalization in children with CHD by 45%, as well as hospital time and oxygen use in those admitted. Thus palivizumab prophylaxis should be considered in young patients with hemodynamically significant CHD.

Predisposition of infants with chronic lung disease to respiratory syncytial virus-induced respiratory failure: a vascular hypothesis

BACKGROUND

Respiratory syncytial virus (RSV) causes the highest rate of severe respiratory infections and mortality in infants and children worldwide. Preterm infants with underlying chronic lung disease (CLD), including bronchopulmonary dysplasia (BPD), are among those at high risk for severe morbidity, long term sequelae and mortality postinfection. The definition of CLD/BPD has evolved and is currently described as a disease of restricted lung development (i.e. impaired alveolar and pulmonary vascular development). This article describes potential mechanisms by which RSV infection causes respiratory failure in the infant with BPD.

METHODS AND RESULTS

The opinions expressed in this article are based on a review of recent investigations into the mechanisms through which RSV infections could cause excessive pulmonary edema formation and subsequent respiratory failure in the infant with CLD. Although alveolar overinflation and atelectasis are well-described patterns of RSV-induced respiratory illness in this infant population, the finding of pulmonary edema is a complex, multifactorial process that is less well understood. Experimental evidence suggests that RSV infection in infants with CLD/BPD not only causes increases in pulmonary vascular reactivity but also precipitates pulmonary edema formation via multiple mechanisms (e.g. nonuniform elevations in pulmonary artery pressure, endothelial injury, alveolar epithelial damage and impairments of native alveolar liquid clearance mechanisms).

CONCLUSIONS

Novel therapies for managing RSV-induced respiratory failure in the infant with CLD/BPD must consider factors responsible for the substantial pulmonary vascular component of this illness.

Bronchiolitis caused by respiratory syncytial virus in an area of portugal: epidemiology, clinical features, and risk factors

The aim of the present study was to analyse the clinical and epidemiological characteristics of bronchiolitis caused by respiratory syncytial virus (RSV) in 225 children observed in a paediatric hospital in Lisbon, Portugal, and to determine the clinical, epidemiological, or laboratory parameters that correlate with greater severity of the disease. This prospective study included hospitalised and ambulatory children younger than 36 months of age with a diagnosis of bronchiolitis and was conducted during two consecutive RSV epidemiological seasons (November-March 2000/01 and 2001/02). The median age of the patients was 5 months, and the male-to-female ratio was 1.6:1. RSV was isolated in 60.9% of patients, predominantly in the hospitalised group. The subtype A:B ratio was 7.4:1 and was similar in both seasons. RSV-positive patients were younger, had more severe clinical forms of bronchiolitis, and fewer changes in leucocyte total and differential counts. Among infected patients, higher clinical severity scores occurred in association with first wheezing episodes, overcrowded households, attendance at day-care centres, or prematurity (<36 weeks). This first prospective study of RSV epidemiology in Portugal provides a foundation for appropriate surveillance programmes of RSV infection in this country. A multicentre study is desirable in order to delineate optimal prophylactic and therapeutic guidelines for RSV infection in Portugal.

Review of epidemiology and clinical risk factors for severe respiratory syncytial virus (RSV) infection

Respiratory syncytial virus (RSV) infection is the most frequent reason for hospitalization of infants in developed countries. Premature birth without or, especially, with chronic lung disease of prematurity, congenital heart disease, and T-cell immunodeficiency are conditions that predispose to more severe forms of RSV infection. Incomplete development of the airway, damage to the airway, and airway hyperreactivity underlie the increased morbidity of RSV infection in prematurely born infants. Pulmonary hypertension and cyanosis are associated with worse outcomes in infants with congenital heart disease, and prolonged viral replication accounts for more severe illness in immunocompromised individuals.

Environmental and demographic risk factors for respiratory syncytial virus lower respiratory tract disease

OBJECTIVE

To critically review the literature examining risk factors for development of severe respiratory syncytial virus lower respiratory tract infection (RSV LRI).

STUDY DESIGN

A literature review was performed with the use of a MedLine search strategy. Clinical evidence of putative risk factors was rated by means of the US Preventive Services Task Force recommendations, and the quality of the data was critically assessed. Nonmedical risk factors examined included race/ethnicity, age of acquisition of RSV, sex, birth during the first half of the RSV season, breast-feeding, malnutrition, maternal education, socioeconomic status, crowding/siblings, day care, and tobacco smoke exposure.

RESULTS

There was sufficient evidence available to conclude that (1) male sex, (2) age <6 months, (3) birth during the first half of the RSV season, (4) crowding/siblings, and (5) day care exposure are significant risk factors for severe RSV LRI. There was insufficient evidence to evaluate the effect of race/ethnicity on severe RSV LRI. The evidence for tobacco smoke exposure is mixed. Low maternal education (as a proxy for lower socioeconomic status), lack of breast-feeding, and malnutrition did not appear to increase the risk of severe RSV LRI or RSV hospitalization.

CONCLUSIONS

Male sex, young age, birth in the first half of the RSV season, day care attendance, and crowding/siblings are independent risk factors for the development of severe RSV LRI.

Palivizumab prophylaxis reduces hospitalization due to respiratory syncytial virus in young children with hemodynamically significant congenital heart disease

OBJECTIVES

To evaluate the safety, tolerance, and efficacy of palivizumab in children with hemodynamically significant congenital heart disease (CHD).

STUDY DESIGN

A randomized, double-blind, placebo-controlled trial included 1287 children with CHD randomly assigned 1:1 to receive 5 monthly intramuscular injections of 15 mg/kg palivizumab or placebo. Children were followed for 150 days. The primary efficacy end point was antigen-confirmed respiratory syncytial virus (RSV) hospitalization.

RESULTS

Palivizumab recipients had a 45% relative reduction in RSV hospitalizations (P=.003), a 56% reduction in total days of RSV hospitalization per 100 children (P=.003), and a 73% reduction in total RSV hospital days with increased supplemental oxygen per 100 children (P=.014). Adverse events were similar in the treatment groups; no child had drug discontinued for a related adverse event. Serious adverse events occurred in 55.4% of palivizumab recipients and 63.1% of placebo recipients (P<.005); none were related to palivizumab. Twenty-one children (3.3%) in the palivizumab group and 27 (4.2%) in the placebo group died; no deaths were attributed to palivizumab. The rates of cardiac surgeries performed earlier than planned were similar in the treatment groups.

CONCLUSIONS

Monthly palivizumab (15 mg/kg IM) was safe, well-tolerated, and effective for prophylaxis of serious RSV disease in young children with hemodynamically significant CHD.

The impact of influenza viruses on hospitalizations in infants younger than two years old during epidemics of respiratory syncytial virus infection

In order to evaluate the association of influenza viruses with hospitalizations for acute respiratory infection in infants younger than two years old during epidemics of respiratory syncytial virus infection, we studied 512 nasal washes from this population. The samples were obtained from 1997 to 2000. A total of 337 viruses were isolated: 264 respiratory syncytial viruses, 62 influenza viruses, eight parainfluenza viruses, two adenovirus and one rhinovirus. Hospitalizations for acute respiratory infection were owing to influenza and respiratory syncytial viruses in 18.3% vs. 78.3% of all cases, and 32.5% vs. 65.8%, respectively, in the group of infants between 6 months and 2 years old.

Evaluation of the safety of palivizumab in the second season of exposure in young children at risk for severe respiratory syncytial virus infection

BACKGROUND

Palivizumab reduces respiratory syncytial virus (RSV) hospitalisations in high-risk infants. Those with severe bronchopulmonary dysplasia may require two seasons of prophylaxis. There is concern that this humanised antibody might cause an adverse immune response in a second season of use.

OBJECTIVE

To evaluate and compare the occurrence of anti-palivizumab antibodies and clinical adverse events in subjects receiving monthly palivizumab injections for a first and second season, and to assess frequency and severity of RSV disease in the two groups.

DESIGN AND PATIENTS

Subjects aged <or=2 years at severe risk for RSV disease were designated as first season (no previous palivizumab exposure) or second season subjects (received palivizumab in previous RSV season). Palivizumab injections (15 mg/kg) were administered monthly for up to 5 months. Anti-palivizumab antibody titres and serum palivizumab concentrations were measured; adverse events were recorded.

RESULTS

No first (n = 71) or second (n = 63) season subjects experienced a significant anti-palivizumab antibody response (titre >or=1 : 80). Serum palivizumab concentrations were similar for the two groups. Nine (12.7%) first season and 8 (12.7%) second season subjects experienced one or more serious adverse events; most were respiratory and all were considered to be not or probably not related to palivizumab. No deaths occurred during the study.

CONCLUSIONS

Monthly palivizumab injections were not associated with adverse immune responses or adverse events in young children receiving palivizumab for one or two seasons. Children receiving palivizumab for a second season did not experience more severe adverse events than those receiving it for the first time.

Detection of human respiratory syncytial virus sequences in peripheral blood mononuclear cells

Peripheral blood mononuclear cells (PBMC) obtained from patients with lower respiratory infections were examined for the detection of human respiratory syncytial virus (RSV) sequences in the N region using the reverse transcription polymerase chain reaction (RT-PCR). RSV infection was confirmed by at least one method, i.e., virus isolation, enzyme immunoassay for viral antigen, and RT-PCR of nasopharyngeal secretions (NPS) samples. The detection rate for RSV RNA in PBMC obtained from RSV-infected patients was 40% (38/94), compared to 5% (1/20) in controls (P = 0.002). Between the groups positive (38) and negative (56) for RSV RNA in PBMC, there was no significant difference in clinical parameters. Seven patients had eight episodes of reinfection and RSV RNA was detected in 50% (4/8) during consecutive infections. Sequences of their PBMC samples were distinct from those of prototype strains of subgroup A and B. However, they were not always consistent with those of paired NPS samples. The findings suggested that RSV RNA could be detected in PBMC even during reinfection and as might have the possibility of quasispecies dynamics, reflecting the nature of RNA viruses.

The complex relationship between respiratory syncytial virus and allergy in lung disease

Epidemiologic studies suggest a strong link between severe respiratory syncytial virus (RSV)-induced bronchiolitis in infancy and allergic disease; however, the mechanisms determining this relationship are currently unknown. In this review article, we summarize data from human clinical studies that explore the association between RSV infection and allergy, some that suggest that RSV bronchiolitis requiring hospitalization leads to an increased incidence of the allergic phenotype and others that suggest that pre-existing allergy is a risk factor for severe RSV bronchiolitis. We also review the published murine models that combine RSV infection and allergic sensitization that attempt to explain the complex relationship between these two factors in regard to lung immunopathology and physiologic dysfunction.

Impact of palivizumab prophylaxis on respiratory syncytial virus hospitalizations in high risk Alaska Native infants

BACKGROUND

Alaska Native children experience extremely high rates of hospitalization for respiratory syncytial virus (RSV) infection. We evaluated the effect of palivizumab prophylaxis on the incidence of RSV hospitalizations in high risk Alaska Native children.

METHODS

We analyzed two retrospective cohorts. The first analysis, of southwest Alaska Native children hospitalized with acute respiratory infections during 1993 to 1996 and 1998 to 2001, compared RSV hospitalization rates among premature and nonpremature infants born before (1993 to 1996) and after (1998 to 2001) palivizumab use. The second analysis, of Alaska Native infants with a history of prematurity or lung disease during 1998 through 2001, compared RSV hospitalization among children receiving palivizumab during protected periods (within 32 days after a dose of palivizumab) and unprotected periods.

RESULTS

First RSV hospitalizations in premature infants from southwest Alaska meeting criteria for palivizumab prophylaxis decreased from 439 per 1000 births before to 150 per 1000 births after palivizumab (relative rate, 0.34; 95% confidence interval, 0.17 to 0.68), whereas the rate in nonpremature infants remained stable (148 per 1000 births compared with 142 per 1000). Among high risk Alaska Native children during 1998 through 2001, the rate of first RSV hospitalization was 0.55 per 1000 protected days and 1.07 per 1000 unprotected days (relative rate, 0.52; 95% confidence interval, 0.28 to 0.93).

CONCLUSIONS

Palivizumab reduced RSV hospitalizations in high risk infants in a region with high rates of RSV hospitalization.

Ribavirin treatment up-regulates antiviral gene expression via the interferon-stimulated response element in respiratory syncytial virus-infected epithelial cells

Respiratory syncytial virus (RSV) is a mucosa-restricted virus that is a leading cause of epidemic respiratory tract infections in children. RSV replication is a potent activator of the epithelial-cell genomic response, influencing the expression of a spectrum of cellular pathways, including proinflammatory chemokines of the CC, CXC, and CX(3)C subclasses. Ribavirin (1-beta-D-ribofuranosyl-1,2,4-triazole-3-carboxamide) is a nontoxic antiviral agent currently licensed for the treatment of severe RSV lower respiratory tract infections. Because ribavirin treatment reduces the cytopathic effect in infected cells, we used high-density microarrays to investigate the hypothesis that ribavirin modifies the virus-induced epithelial genomic response to replicating virus. Ribavirin treatment administered in concentrations of 10 to 100 micro g/ml potently inhibited RSV transcription, thereby reducing the level of RSV N transcripts to approximately 13% of levels in nontreated cells. We observed that in both the absence and the presence of ribavirin, RSV infection induced global alterations in the host epithelial cell, affecting approximately 49% of the approximately 6,650 expressed genes detectable by the microarray. Ribavirin influences the expression of only 7.5% of the RSV-inducible genes (total number of genes, 272), suggesting that the epithelial-cell genetic program initiated by viral infection is independent of high-level RSV replication. Hierarchical clustering of the ribavirin-regulated genes identified four expression patterns. In one group, ribavirin inhibited the expression of the RSV-inducible CC chemokines MIP-1 alpha and -1 beta, which are important in RSV-induced pulmonary pathology, and interferon (IFN), a cytokine important in the mucosal immune response. In a second group, ribavirin further up-regulated a set of RSV- and IFN-stimulated response genes (ISGs) encoding antiviral proteins (MxA and p56), complement products, acute-phase response factors, and the STAT and IRF transcription factors. Because IFN-beta expression itself was reduced in the ribavirin-treated cells, we further investigated the mechanism for up-regulation of the IFN-signaling pathway. Enhanced expression of IFI 6-16, IFI 9-27, MxA/p78, STAT-1 alpha, STAT-1 beta, IRF-7B, and TAP-1-LMP2 transcripts were independently reproduced by Northern blot analysis. Ribavirin-enhanced TAP-1-LMP2 expression was a transcriptional event where site mutations of the IFN-stimulated response element (ISRE) blocked RSV and ribavirin-inducible promoter activity. Furthermore, ribavirin up-regulated the transcriptional activity of a reporter gene selectively driven by the ISRE. In specific DNA pull-down assays, we observed that ribavirin enhanced RSV-induced STAT-1 binding to the ISRE. We conclude that ribavirin potentiates virus-induced ISRE signaling to enhance the expression of antiviral ISGs, suggesting a mechanism for the efficacy of combined treatment with ribavirin and IFN in other chronic viral diseases.

Emergency department presentations of pediatric congenital heart disease

Numerous studies have described the pathophysiology, clinical manifestations, and treatment of the many forms of congenital heart disease (CHD), but none has specifically addressed the reasons CHD patients present to the Emergency Department (ED). The objective of this study was to provide a descriptive analysis of the ED presentations of acute and seriously ill pediatric CHD patients. We intended to capture a subset of acutely ill CHD patients who had presenting signs and symptoms that were potentially attributable to their underlying CHD. Recognizing the more common presentation patterns for patients with CHD may be of benefit. Adhering to the basic principles of airway, breathing and circulatory (ABC) management is essential when caring for critically ill CHD patients. Patients with complex CHD are often very difficult to correctly diagnose and manage in the ED. They often require extensive inpatient observation and evaluation. A low threshold for inpatient management of these high-risk patients is warranted.

Clinical experience with respiratory syncytial virus vaccines

Respiratory syncytial virus (RSV) infection is at times associated with life-threatening lower respiratory tract illness in infancy. Severe infection during the first year of life may be an important risk factor or indicator for the development of asthma in early childhood. Severe infections primarily occur in healthy infants, and young infants and children with specific risk factors. However, RSV causes respiratory infections in all age groups. Indeed it is now recognized that RSV disease is responsible for significant morbidity and mortality in the geriatric population. RSV infection remains difficult to treat, and prevention is a worldwide goal. For this reason there has been an intensive effort to develop an effective and safe RSV vaccine. Initial infection with RSV affords limited protection to reinfection, yet repeated episodes decrease the risk for lower respiratory tract illness. In the 20 years from 1960 to 1980, trials of several candidate RSV vaccines failed to attain the desired safety and protection against natural infection. Some vaccine types either failed to elicit immunogenicity, as with the live subcutaneous vaccine, or resulted in exaggerated disease on natural exposure to the virus, as with the formalin-inactivated (FI) type. Currently vaccine candidates are being developed based on the molecular virology of RSV. Recent formulations of candidate RSV vaccines have focused on subunit vaccines [such as purified fusion protein (PFP)], subunit vaccines combined with nonspecific immune activating adjuvants, live attenuated vaccines (including cold passaged, temperature-sensitive or cpts mutants), genetically engineered live attenuated vaccines and polypeptide vaccines.

Replication and clearance of respiratory syncytial virus: apoptosis is an important pathway of virus clearance after experimental infection with bovine respiratory syncytial virus

Human respiratory syncytial virus is an important cause of severe respiratory disease in young children, the elderly, and in immunocompromised adults. Similarly, bovine respiratory syncytial virus (BRSV) is causing severe, sometimes fatal, respiratory disease in calves. Both viruses are pneumovirus and the infections with human respiratory syncytial virus and BRSV have similar clinical, pathological, and epidemiological characteristics. In this study we used experimental BRSV infection in calves as a model of respiratory syncytial virus infection to demonstrate important aspects of viral replication and clearance in a natural target animal. Replication of BRSV was demonstrated in the luminal part of the respiratory epithelial cells and replication in the upper respiratory tract preceded the replication in the lower respiratory tract. Virus excreted to the lumen of the respiratory tract was cleared by neutrophils whereas apoptosis was an important way of clearance of BRSV-infected epithelial cells. Neighboring cells, which probably were epithelial cells, phagocytized the BRSV-infected apoptotic cells. The number of both CD4(+) and CD8+ T cells increased during the course of infection, but the T cells were not found between the epithelial cells of the bronchi up until apoptosis was no longer detected, thus in the bronchi there was no indication of direct contact-dependent T-cell-mediated cytotoxicity in the primary infection.

Differences in admission rates of children with bronchiolitis by pediatric and general emergency departments

OBJECTIVE

It is uncertain whether pediatric and general emergency departments have different admitting practices regarding children with bronchiolitis. The objective of this study was to quantify the differences in admission practices between pediatric and general emergency departments of children with bronchiolitis in 1 North American metropolitan area, controlling for various factors such as clinical severity, comorbid conditions, and socioeconomic status.

DESIGN

Retrospective cohort review of emergency department visits from April 1992 to March 1997.

SETTING

Five emergency departments (1 pediatric and 4 general) serving the Calgary Health Region, which encompasses approximately 850 000 people.

PATIENTS

All children residing within the region who visited a regional emergency department and were diagnosed to have bronchiolitis (International Classification of Diseases, Ninth Revision code 466.1, primary or secondary diagnosis).

MAIN OUTCOME MEASURE

Population-standardized estimates of admission rates.

RESULTS

The medical charts of 3091 children diagnosed to have bronchiolitis during the study period were reviewed. Of this number, 2496 children were evaluated at the pediatric emergency department, and 629 (25%) were admitted. The remaining 595 (19%) were evaluated at the general emergency departments, and 221 (37%) were admitted. Controlling for age, gender, estimated family income based on postal code, medical comorbidity, and clinical severity estimated by presenting respiratory rate and room air oxygen saturation, population-standardized estimates for admission rates at the pediatric and general emergency departments were 24% (standard error: 1%) and 43% (standard error: 2%), respectively.

CONCLUSION

Children diagnosed to have bronchiolitis at the Calgary Health Region's pediatric emergency department were about half as likely to be admitted to the hospital as children diagnosed at the region's general emergency departments.

Respiratory syncytial virus infection in Navajo and White Mountain Apache children

OBJECTIVE

The hospitalization rate for bronchiolitis of any cause among US children younger than 1 year is estimated at 31.2 per 1000. No data exist on respiratory syncytial virus (RSV)-specific hospitalization rates among high-risk Native Americans other than Alaska Natives, for whom the incidence of RSV hospitalization was estimated at 150 per 1000 among infants younger than 1 year. We aimed to estimate RSV hospitalization rates among Navajo and White Mountain Apache children younger than 2 years.

METHODS

We conducted prospective population-level hospital-based surveillance to determine RSV hospitalization rates among Navajo and White Mountain Apache children younger than 2 years. From 1997 to 2000, all children who were admitted for acute lower respiratory tract infection between October 1 and March 31 had a nasopharyngeal aspirate obtained and tested for RSV by commercial enzyme immunoassay kits. We reviewed charts of children who tested positive for RSV antigen to determine disease severity.

RESULTS

During 3 RSV seasons (1997-2000), 51.3% of 1837 admissions for acute lower respiratory tract infection among children younger than 2 years were attributed to RSV infection. The overall seasonal RSV hospitalization rate among children younger than 2 years was 63.6 per 1000 and 91.3 per 1000 among children younger than 1 year. In a univariate analysis, predictors of severity included age <6 months (relative risk: 6.8; 95% confidence interval: 3.1-17.0).

CONCLUSIONS

Navajo and White Mountain Apache children are at high risk for RSV disease requiring hospitalization. A lower threshold for hospitalization or underlying chronic conditions that predispose to severe RSV disease do not seem to explain high RSV hospitalization rates in this population.

Current concepts on active immunization against respiratory syncytial virus for infants and young children

Respiratory syncytial virus (RSV) is the most important causative agent of viral respiratory tract infections in infants and young children. Passive immunization against RSV became available recently, but this does not apply to an effective vaccine as a result of dramatic adverse results of immunization with a RSV candidate vaccine in the 1960s and the lack of full knowledge of the immune response induced by RSV. Nonetheless intensive research during the past two decades has resulted in several interesting candidate vaccines, of which some have gone through testing in humans. These include the subunit vaccines PFP-1, PFP-2, BBG2Na and cold-passaged/temperature-sensitive mutants. The development of candidate vaccines against RSV is discussed. Because of questions, uncertainties and difficulties with the development of effective vaccines against RSV, it will probably be at least another 5 to 10 years before routine immunization against RSV becomes available.

Respiratory syncytial virus infections in children and adults

Respiratory syncytial virus is the leading cause of hospital admission for lower respiratory tract infection in young children and appears to be responsible for a significant burden of disease in adults, particularly the elderly and the immunocompromised. In this review, we describe the epidemiology, diagnosis and clinical manifestations of infection attributed to this virus. We also consider current therapeutic and prophylactic options and appraise strategies for vaccination that are in clinical trials.

Prevention of respiratory syncytial virus infections in high-risk infants by monoclonal antibody (palivizumab)

Respiratory syncytial virus (RSV) is a major viral pathogen which causes serious respiratory illness in infants and children worldwide. Palivizumab (Synagis) is an anti-RSV monoclonal antibody administered intramuscularly for the prevention of severe RSV respiratory disease in high-risk infants and young children. The IMpact-RSV trial, the pivotal multicenter, randomized, placebo-controlled trial performed in the USA, Canada and the United Kingdom demonstrated an overall 55% reduction in hospitalization rate due to RSV infection in preterm infants (< or = 35 weeks gestation) with and without chronic lung disease (CLD). Subgroup analysis in premature infants without CLD revealed an even greater reduction in RSV hospitalization rates (78%). Adverse events were infrequent and did not differ between placebo and palivizumab groups. Injection site reactions were infrequent and mild; no differences were observed between palivizumab and placebo subjects. Palivizumab does not interfere with administration of other pediatric vaccines. Comprehensive parent education programs regarding prevention of infection, avoidance of risk factors for infection, careful adherence to infection control policies, and recognition of early symptoms of RSV infection remain important components of RSV prevention strategies. In light of the lack of effective vaccines for this serious health risk, palivizumab offers the only option for prophylaxis against RSV disease in high-risk infants.

Prevalence of respiratory syncytial virus infection in Italian infants hospitalized for acute lower respiratory tract infections, and association between respiratory syncytial virus infection risk factors and disease severity

This study was designed to collect data on the prevalence of respiratory syncytial virus (RSV) infection in Italy in infants hospitalized for lower respiratory tract infections, and to evaluate which of the recognized risk factors might be associated with disease severity. Thirty-two centers throughout Italy participated in the study. Over a 6-month period (November 1,1999 to April 30, 2000), we evaluated all children < 2 years of age hospitalized for lower respiratory tract infections. All subjects were tested for RSV within 24 hr of hospitalization by using an immuno-enzymatic diagnostic test (Abbott Testpack, RSV). Logistic regression was used to identify the factors that might be associated with more severe disease or could increase the likelihood of RSV positivity in hospitalized infants. Out of a total of 1,232 children enrolled, 40.6% were found to be RSV-positive (RSV+). The peak of the RSV epidemic occurred in February, while the lowest prevalence of RSV positivity was seen in November (P < 0.05). A high proportion of study subjects had low birth weight and low gestational age. The clinical diagnosis at hospitalization was bronchiolitis in 66.7%, pneumonia in 15.3%, and wheezy bronchitis in 18.1%. In the bronchiolitis group, a higher prevalence of RSV+ was found in patients with gestational age <or= 33 weeks or 34-35 weeks, as compared to those with a gestational age >or= 36 weeks (P < 0.04). No differences were found in the proportion of RSV+ patients in the three gestational age subgroups with pneumonia and wheezy bronchitis (P > 0.05, each comparison). Independent of the clinical diagnosis at admission, RSV infection was associated with more severe respiratory impairment. Environmental smoke exposure was higher in subjects with bronchiolitis than in those with wheezy bronchitis (P < 0.04), and RSV+ was positively related with the birth order (P < 0.05). The presence of older siblings and birth order plays an important role in RSV infection. The collected data show that, in Italy, RSV is an important cause of lower respiratory tract infection in infants. Gestational age, birth order, birth weight, and exposure to tobacco smoke affected the prevalence and severity of RSV-related lower respiratory tract disease.

Multiplex assay for detection of strain-specific antibodies against the two variable regions of the G protein of respiratory syncytial virus

The role of strain differences in respiratory syncytial virus (RSV) disease has not been clearly defined. To investigate the possibility that strain differences contribute to susceptibility to repeat infections, we developed assays to detect antibodies to the two variable regions of the RSV G protein by cloning and expressing the internal variable region at amino acids (aa) 60 to 172 (g1) and the carboxy-terminal variable region at aa 193 to the carboxy terminus (g2) from different genotypes of RSV. The purified proteins were covalently linked to beads with different proportions of red and orange fluorescent dyes and reacted against serum specimens. Antibody reacting against the differently colored beads, and thus against different G polypeptides, was detected by use of flow cytometry and the Luminex system. This assay system detected group- and, to some extent, genotype-specific responses to RSV infection and can be used to investigate the role of strain differences in RSV disease.

Genetic susceptibility to respiratory syncytial virus infection in inbred mice

Differences in the severity of respiratory syncytial virus (RSV)-induced lower respiratory disease in infants have been attributed to multiple environmental and genetic factors. To identify the genetic factor(s) influencing RSV susceptibility, we examined RSV infection in eight inbred mouse strains. Lung RSV titers differed significantly between mouse strains: the RSV titers were 15-fold higher in AKR/J (permissive) mice compared with C57BL/6J (resistant) mice at 4 days after inoculation. This strain-specific difference in RSV titers suggested that susceptibility to RSV infection was attributable to genetic differences between strains. To examine the mode of inheritance of RSV susceptibility, F1 and backcross (F1 x AKR/J) progeny were infected and RSV titers determined. RSV titers in the F1 progeny were similar to those found in the resistant (C57BL/6J) parent, suggesting resistance was inherited as a dominant trait. The distribution of RSV titers in backcross progeny were discordant with that predicted for a single gene effect, suggesting susceptibility was influenced by more than one gene. These data suggest that RSV susceptibility is a multigenic trait that should be amenable to resolution by genomic analysis.

Risk factors for severe respiratory syncytial virus infection among Alaska native children

OBJECTIVE

The incidence of hospitalization for respiratory syncytial virus (RSV) infection among Alaska Native children is much higher than among non-Native populations in the United States. We conducted this study to better understand factors associated with hospitalization attributable to RSV infection in this high-risk population.

DESIGN

Case-control study, including collection of cord blood for RSV-neutralizing antibody measurement.

SETTING

Remote region of southwest Alaska served by 1 regional hospital and 2 referral hospitals.

SUBJECTS

Case-patients identified through surveillance for RSV infection and matched control subjects without acute respiratory infection hospitalization.

RESULTS

Breastfeeding was associated with a lower risk of RSV hospitalization (odds ratio: 0.34), whereas underlying medical conditions (primarily prematurity) were associated with increased risk (odds ratio: 6.25). Environmental factors associated with a higher risk of hospitalization included household crowding (4 or more children in the household and crowding index > or =2). The level of maternal RSV-neutralizing antibody was not associated with the risk of hospitalization.

CONCLUSIONS

In this region with extremely high risk of RSV hospitalization, several measures, such as encouraging breastfeeding and reducing household crowding, could reduce the risk of hospitalization attributable to RSV.

Antiviral Chinese medicinal herbs against respiratory syncytial virus

Forty-four medicinal herbs were tested for antiviral activities against respiratory syncytial virus (RSV) by means of the cytopathologic effect (CPE) assay. Twenty-seven of the 44 medicinal herbs showed potent or moderate antiviral activities against RSV with 50% inhibition concentration (IC(50)) ranging from 6.3 to 52.1 microg/ml, and with selectivity index (SI) ranging from 2.0 to 32.1. Further purification of the active extracts from Sophora flavescens Ait. and Scutellaria baicalensis Georgi led to the identification of anagyrine (2), oxymatrine (7), sophoranol (10), wogonin (12), and oroxylin A (13) as the potent anti-RSV components.