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

A decade of respiratory syncytial virus epidemiology and prophylaxis: translating evidence into everyday clinical practice

Respiratory syncytial virus (RSV) is a common infection in infancy, with nearly all children affected by two years of age. Approximately 0.5% to 2.0% of all children are hospitalized with lower respiratory tract disease, of which 50% to 90% have bronchiolitis and 5% to 40% have pneumonia. Morbidity and mortality are highest in children with nosocomial infection and in those with underlying medical illnesses such as cardiac and chronic lung disease. Aboriginal children residing in remote northern regions are specifically considered to be at high risk for hospitalization due to RSV infection. Thorough hand washing and health education are the principal strategies in primary prevention. In the absence of a vaccine, palivizumab prophylaxis is currently the best intervention to reduce the burden of illness and RSV-related hospitalization in high-risk children. Health care professionals should provide palivizumab prophylaxis cost effectively in accordance with recommendations issued by pediatric societies and national advisory bodies. The present article reviews the epidemiology of RSV infection and the short- and long-term impact of disease in high-risk infants and special populations. Prevention strategies and treatment are discussed based on the existing scientific evidence, and future challenges in the management of RSV infection are addressed.

The multicenter Italian birth cohort study on incidence and determinants of lower respiratory tract infection hospitalization in infants at 33 weeks GA or more: preliminary results

BACKGROUND

Respiratory syncytial virus (RSV) causes respiratory infections during the first year of life. Very premature infants have more severe diseases and also 'late preterm infants' may be more susceptible to the infection.

AIM OF THE STUDY

To evaluate in an Italian cohort the incidence and risk factors of severe hospitalized lower respiratory tract infection (LRTI) induced or not by RSV during the first year of life.

METHODS

A cohort of 33(+0d)-34(+6d) wGA newborns paired with two sex- and age-matched 35(+0d)-37(+6d) wGA and ≥ 38(+0d) wGA newborns were enrolled. Hospitalization for LRTI induced or not by RSV during the first year of life was assessed through phone interview at the end of the RSV season (November-March) and at the completion of the first year of life. The parents were asked to report hospitalization for any reason.

RESULTS

1064 neonates were enrolled (November 2009-October 2010), 697 had at least one phone follow-up by September 2010. Babies of 33(+0d)-34(+6d) wGA were more frequently conceived through assisted fertilization technologies, born from cesarean delivery had more frequently acute perinatal risk factors and were more frequently twins. After a mean 6 month-follow-up, we registered 29 hospitalizations for LRTI induced or not by RSV. Hospitalizations were slightly and non-significantly more frequent in 33(+0d)-37(+6d) wGA infants. The risk of hospitalization was significantly 60% reduced in breastfed babies and four folds significantly increased during the RSV season.

CONCLUSION

The very preliminary data of this ongoing study suggest that in 'late-preterm' infants some individual/environmental characteristics of the infants play a relevant role in determining the risk of severe RSV infection.

Detection of respiratory syncytial virus using nanoparticle amplified immuno-polymerase chain reaction

In traditional immuno-polymerase chain reaction (immuno-PCR), a single antibody recognition event is associated with one to three DNA tags, which are subsequently amplified by PCR. Here we describe a nanoparticle-amplified immuno-PCR (NPA-IPCR) assay that combines antibody recognition of enzyme-linked immunosorbent assay (ELISA) with a 50-fold nanoparticle valence amplification step prior to tag amplification by PCR. The assay detects a respiratory syncytial virus (RSV) surface protein using an antibody bound to a 15-nm gold nanoparticle cofunctionalized with thiolated DNA complementary to a hybridized 76-base tag DNA with a tag DNA/antibody ratio of 50:1. The presence of virus particles triggers the formation of a "sandwich" complex composed of the gold nanoparticle construct, virus, and an antibody-functionalized magnetic particle used for extraction. After extraction, DNA tags are released by heating to 95°C and detected via real-time PCR. The limit of detection of the assay was compared with ELISA and reversion transcription (RT) PCR using RSV-infected HEp-2 cell extracts. NPA-IPCR showed an approximately 4000-fold improvement in the limit of detection compared with ELISA and a 4-fold improvement compared with viral RNA extraction followed by traditional RT-PCR. NPA-IPCR offers a viable platform for the development of early-stage diagnostics requiring an exceptionally low limit of detection.

Prevention of serious respiratory syncytial virus-related illness. I: Disease pathogenesis and early attempts at prevention

Respiratory syncytial virus (RSV) was first described 160 years ago but was not officially recognized as a cause of serious illness in children until the late 1950s. It has been estimated that virtually all children have had at least one RSV infection by their second birthday. RSV is responsible for annual disease outbreaks, usually during a defined winter seasonal period that can vary by community and year. RSV is recognized as the leading cause of hospitalization among young children worldwide. Infants of young chronologic age and children with predisposing factors, such as premature birth, pulmonary disease, or congenital heart disease, are most susceptible to serious illness. Unlike other viruses, immunity to RSV infection is incomplete and short lived, and reinfection is common throughout life. Initial attempts to develop a vaccine in the 1960s met with unexpected and tragic results; many children vaccinated with a formalin-inactivated wild-type virus developed serious pulmonary disease upon subsequent natural infection. Numerous other vaccine technologies have since been studied, including vectored approaches, virus-like particles, DNA vaccines, and live attenuated virus vaccine. As of early 2010, only two companies or institutions had RSV vaccine candidates in early clinical trials, and no vaccine is likely to be licensed for marketing in the immediate future.

Lactobacillus-mediated priming of the respiratory mucosa protects against lethal pneumovirus infection

The inflammatory response to respiratory virus infection can be complex and refractory to standard therapy. Lactobacilli, when targeted to the respiratory epithelium, are highly effective at suppressing virus-induced inflammation and protecting against lethal disease. Specifically, wild-type mice primed via intranasal inoculation with live or heat-inactivated Lactobacillus plantarum or Lactobacillus reuteri were completely protected against lethal infection with the virulent rodent pathogen, pneumonia virus of mice; significant protection (60% survival) persisted for at least 13 wk. Protection was not unique to Lactobacillus species, and it was also observed in response to priming with nonpathogenic Gram-positive Listeria innocua. Priming with live lactobacilli resulted in diminished granulocyte recruitment, diminished expression of multiple proinflammatory cytokines (CXCL10, CXCL1, CCL2, and TNF), and reduced virus recovery, although we have demonstrated clearly that absolute virus titer does not predict clinical outcome. Lactobacillus priming also resulted in prolonged survival and protection against the lethal sequelae of pneumonia virus of mice infection in MyD88 gene-deleted (MyD88(-/-)) mice, suggesting that the protective mechanisms may be TLR-independent. Most intriguing, virus recovery and cytokine expression patterns in Lactobacillus-primed MyD88(-/-) mice were indistinguishable from those observed in control-primed MyD88(-/-) counterparts. In summary, we have identified and characterized an effective Lactobacillus-mediated innate immune shield, which may ultimately serve as critical and long-term protection against infection in the absence of specific antiviral vaccines.

Time series model to predict burden of viral respiratory illness on a pediatric intensive care unit

BACKGROUND

In the United States, viral respiratory infections are a leading cause of illness and hospitalization in young children. Caring for children with severe viral respiratory illness can have a substantial impact on resource utilization in the pediatric intensive care unit (PICU). The objective was to build a robust model that captures the periodicity of severe pediatric viral respiratory illness and forecasts the incidence of viral respiratory illness in the PICU.

METHODS

This was a retrospective time series analysis in a PICU at a quaternary care children's hospital. Patients were less than 18 years of age with laboratory-confirmed respiratory syncytial virus, influenza, parainfluenza, or adenovirus infection on or during admission from October 2002 to September 2008. Time series modeling techniques were to used to model viral incidence, using maximum likelihood estimation to identify model parameters.

RESULTS

A total of 289 patients were included in the analysis. An autoregressive model of order 10 that included an exogenous variable of community viral incidence from the previous month was able to explain and predict viral incidence in the PICU. A limitation of the study was that it included a single institution.

CONCLUSIONS

The identified model, derived from historical data from both a PICU and the local community, produced accurate 1-month and 3-month forecasts of severe viral respiratory illness presentation to the PICU. These results suggest that time series models may be useful tools in forecasting the burden of severe viral respiratory illness at the institutional level, helping institutions make decisions to optimize the distribution of resources.

Two novel fusion inhibitors of human respiratory syncytial virus

To search for novel drugs against human respiratory syncytial virus (RSV), we have screened a diversity collection of 16,671 compounds for anti-RSV activity in cultures of HEp-2 cells. Two of the hit compounds, i.e., the N-(2-hydroxyethyl)-4-methoxy-N-methyl-3-(6-methyl[1,2,4]triazolo[3,4-a]phthalazin-3-yl)benzenesulfonamide (designated as P13) and the 1,4-bis(3-methyl-4-pyridinyl)-1,4-diazepane (designated as C15), reduced the virus infectivity with IC₅₀ values of 0.11 and 0.13μM respectively. The concentration of P13 and C15 that reduced the viability of HEp-2 cells by 50% was 310 and 75μM respectively. Both P13 and C15 exhibited no direct virucidal activity or inhibitory effects on the virus attachment to cells. However, to inhibit formation of RSV-induced syncytial plaques P13 and C15 had to be present during the virus entry into the cells and the cell-to-cell transmission of the virus. The RSV multiplication in HEp-2 cells in the presence of P13 or C15 resulted in rapid selection of viral variants that were ∼1000 times less sensitive to these drugs than original virus. Sequencing of resistant viruses revealed presence of amino acid substitutions in the F protein of RSV, i.e., the D489G for C15-selected, and the T400I and N197T (some clones) for the P13-selected virus variants. In conclusion, we have identified two novel fusion inhibitors of RSV, and the detailed understanding of their mode of antiviral activity including selection for the drug resistant viral variants may help to develop selective and efficient anti-RSV drugs.

Nationwide survey of severe respiratory syncytial virus infection in children who do not meet indications for palivizumab in Japan

In Japan, palivizumab, a humanized monoclonal antibody specific for respiratory syncytial virus (RSV), has been available since 2002. However, its use is limited to children at risk of severe RSV infection, with specific criteria that have been validated in large-scale clinical studies. The Pharmaceutical Committee of the Japan Pediatric Society established a committee to conduct a nationwide questionnaire survey to determine which diseases place children at risk of severe RSV infection and require preventive measures. A questionnaire sent to 613 medical institutions, including major pediatric hospitals and general hospitals with pediatric services, received 272 responses (44.4%). In total, 1,115 children not meeting current indications for palivizumab therapy were hospitalized for severe RSV infection, 16 (1.4%) of whom died; this suggests that palivizumab therapy should be considered for children with severe immunodeficiency or those at risk of nosocomial RSV infection in whom prevention of RSV infection by standard control measures appears difficult.

The distinguishing features of human metapneumovirus and respiratory syncytial virus

Acute respiratory tract infections (RTIs) are a leading cause of morbidity and mortality worldwide. Human Metapneumovirus (hMPV) is a member of the Metapneumovirus genus within the Pneumovirinae subfamily of the Paramyxoviridae family. Though hMPV was only discovered in 2001, a large body of work has already shown that it is the aetiologic agent of a substantial proportion of upper and lower RTIs across all age groups in both healthy and immunocompromised hosts throughout the world. RSV, also a pneumovirus, is the human pathogen most closely related to hMPV. RSV is the leading cause of pneumonia and bronchiolitis in infants and young children, but can also cause respiratory tract disease in all age groups. In this paper, we will review the salient features of the virology, epidemiology, pathogenesis, host immune responses, clinical manifestations and diagnostic modalities of hMPV, using RSV as a comparison. In addition, we will show how immunoprophylactic and therapeutic strategies studied and used in clinical practice for RSV-some with great success, and others tragic failure-have led to promising areas of research for the prevention and treatment of the significant burden of disease caused by hMPV.

Prophylactic treatment with a G glycoprotein monoclonal antibody reduces pulmonary inflammation in respiratory syncytial virus (RSV)-challenged naive and formalin-inactivated RSV-immunized BALB/c mice

We examined whether prophylactically administered anti-respiratory syncytial virus (anti-RSV) G monoclonal antibody (MAb) would decrease the pulmonary inflammation associated with primary RSV infection and formalin-inactivated RSV (FI-RSV)-enhanced disease in mice. MAb 131-2G administration 1 day prior to primary infection reduced the pulmonary inflammatory response and the level of RSV replication. Further, intact or F(ab')(2) forms of MAb 131-2G administered 1 day prior to infection in FI-RSV-vaccinated mice reduced enhanced inflammation and disease. This study shows that an anti-RSV G protein MAb might provide prophylaxis against both primary infection and FI-RSV-associated enhanced disease. It is possible that antibodies with similar reactivities might prevent enhanced disease and improve the safety of nonlive virus vaccines.

Inefficient lymph node sensitization during respiratory viral infection promotes IL-17-mediated lung pathology

Development of bronchus-associated lymphoid tissue has been suggested to enhance local antiviral immune responses; however, ectopic lymph node formation often corresponds to chronic inflammatory diseases. These studies investigated the role of ectopic pulmonary lymph nodes upon respiratory syncytial virus (RSV) infection using CCR7-deficient mice, which develop bronchus-associated lymphoid tissue early in life. CCR7(-/-) mice exhibited impaired secondary lymph node formation, enhanced effector T cell responses and pathogenic mucus production in the lung after RSV infection. IL-17 production from CD4 T cells in CCR7(-/-) mice was most remarkably enhanced. Wild-type animals reconstituted with CCR7(-/-) bone marrow recapitulated the pathogenic lung phenotype in CCR7(-/-) mice, whereas CCR7(-/-) animals reconstituted with wild-type bone marrow had normal lymph node development, diminished IL-17 production and reduced lung pathology. Mixed bone marrow chimeras revealed an alteration of immune responses only in CCR7(-/-) T cells, suggesting that impaired trafficking promotes local effector cell generation. Lymphotoxin-α-deficient mice infected with RSV were used to further examine locally induced immune responses and demonstrated increased mucus production and amplified cytokine responses in the lung, especially IL-17. Neutralization of IL-17 in CCR7(-/-) or in lymphotoxin-α-deficient animals specifically inhibited mucus hypersecretion and reduced IL-13. Thus, immune cell trafficking to secondary lymph nodes is necessary for appropriate cytokine responses to RSV as well as modulation of the local environment.

Partner violence during pregnancy: prevalence, effects, screening, and management

The purpose of this review is to provide an overview of the current state of knowledge regarding the experience of intimate partner violence (IPV) during pregnancy. Pregnancy IPV is a significant problem worldwide, with rates varying significantly by country and maternal risk factors. Pregnancy IPV is associated with adverse newborn outcomes, including low birth weight and preterm birth. Many mechanisms for how IPV may impact birth outcomes have been proposed and include direct health, mental health, and behavioral effects, which all may interact. Screening for IPV during pregnancy is essential, yet due to time constraints and few clear recommendations for assessment, many prenatal providers do not routinely inquire about IPV, or even believe they should. More training is needed to assist health care providers in identifying and managing pregnancy IPV, with additional research needed to inform effective interventions to reduce the rates of pregnancy IPV and resultant outcomes.

Respiratory virus-induced TLR7 activation controls IL-17-associated increased mucus via IL-23 regulation

The response to respiratory syncytial virus (RSV), negative strand ssRNA virus, depends upon the ability to recognize specific pathogen-associated targets. In the current study, the role of TLR7 that recognizes ssRNA was examined. Using TLR7(-/-) mice, we found that the response to RSV infection in the lung was more pathogenic as assessed by significant increases in inflammation and mucus production. Although there appeared to be no effect of TLR7 deficiency on type I IFN, the pathology was associated with an alteration in T cell responses with increases in mucogenic cytokines IL-4, IL-13, and IL-17. Examination of dendritic cells from TLR7(-/-) animals indicated a preferential activation of IL-23 (a Th17-promoting cytokine) and a decrease in IL-12 production. Neutralization of IL-17 in the TLR7(-/-) mice resulted in a significant decrease in the mucogenic response in the lungs of the RSV-infected mice. Thus, without TLR7-mediated responses, an altered immune environment ensued with a significant effect on airway epithelial cell remodeling and goblet cell hyper/metaplasia, leading to increased mucus production.

TSLP from RSV-stimulated rat airway epithelial cells activates myeloid dendritic cells

The respiratory syncytial virus (RSV) is a primary cause of lower respiratory tract infections in children, the elderly and in people who are immune suppressed, and is also the cause for the development of asthma primarily in infants. However, the immunological mechanisms by which RSV enhances allergic sensitization and asthma remain unclear. The aim of this study was to examine the influence of RSV-infected airway epithelial cells on the activation and functions of rat myeloid dendritic cells (mDCs).We found that the exposure of primary rat airway epithelial cells (PRAECs) to RSV induced a rapid (6 h), high (12 h) and persistent (18 h) increase in thymic stromal lymphopoietin (TSLP) mRNA compared with untreated PRAECs. TSLP protein expression was also enhanced by RSV infection. Functional maturation of mDCs was induced by RSV-treated PRAECs, as shown by their enhanced levels of OX40L and thymus- and activation-regulated chemokine (TARC) mRNAs, which increased the expressions of major histocompatibility complex II (MHCII) and CD86 costimulatory molecules and promoted enhanced T-cell proliferation in mixed lymphocyte reactions. These activities were inhibited in cocultures with RSV-infected RTECs (rat tracheal epithelial cells, an immortalized cell strain) that had been pretreated with TSLP-targeted small interfering RNA. These results suggest that RSV can induce epithelial cells to produce TSLP, which in turn promotes the maturation of mDCs that might support Th2 cell polarization.

New insights for development of a safe and protective RSV vaccine

Respiratory Syncytial Virus (RSV) is the leading cause of pneumonia and bronchiolitis in infants and children <1 year old, resulting in significant morbidity and mortality worldwide. There is currently no RSV vaccine. In the 1960s, a formalin-inactivated RSV (FI-RSV) vaccine trial led to exacerbated disease upon natural infection of vaccinees, including two deaths. The causes involved in the disastrous results of these vaccine trials are still unclear but they remain the engine for searching new avenues to develop a safe vaccine that can provide long-term protection against this important pathogen. This article reviews some of the early history of RSV vaccine development,as well as more recent information on the interaction between RSV and the host innate and adaptive immune responses. A safe and efficacious vaccine for RSV will require "re-education" of the host immune response against RSV to prevent vaccine-enhanced or severe RSV disease.

Control of RSV-induced lung injury by alternatively activated macrophages is IL-4R alpha-, TLR4-, and IFN-beta-dependent

Severe respiratory syncytial virus (RSV)-induced bronchiolitis has been associated with a mixed "Th1" and "Th2" cytokine storm. We hypothesized that differentiation of "alternatively activated" macrophages (AA-M phi) would mediate the resolution of RSV-induced lung injury. RSV induced interleukin (IL)-4 and IL-13 by murine lung and peritoneal macrophages, IL-4R alpha/STAT6-dependent AA-M phi differentiation, and significantly enhanced inflammation in the lungs of IL-4R alpha(-/-) mice. Adoptive transfer of wildtype macrophages to IL-4R alpha(-/-) mice restored RSV-inducible AA-M phi phenotype and diminished lung pathology. RSV-infected Toll-like receptor (TLR)4(-/-) and interferon (IFN)-beta(-/-) macrophages and mice also failed to express AA-M phi markers, but exhibited sustained proinflammatory cytokine production (e.g., IL-12) in vitro and in vivo and epithelial damage in vivo. TLR4 signaling is required for peroxisome proliferator-activated receptor gamma expression, a DNA-binding protein that induces AA-M phi genes, whereas IFN-beta regulates IL-4, IL-13, IL-4R alpha, and IL-10 expression in response to RSV. RSV-infected cotton rats treated with a cyclooxygenase-2 inhibitor increased expression of lung AA-M phi. These data suggest new treatment strategies for RSV that promote AA-M phi differentiation.

Heliox inhalation therapy for bronchiolitis in infants

BACKGROUND

Acute viral bronchiolitis is associated with airway obstruction and turbulent gas flow. Heliox, a mixture of oxygen and the inert gas helium, may improve gas flow through high-resistance airways and decrease the work of breathing.

OBJECTIVES

To assess heliox in addition to standard medical care for acute bronchiolitis in infants.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2009, issue 2), which includes the Cochrane Acute Respiratory Infections (ARI) Group's Specialised Register, MEDLINE (1966 to June 2009), EMBASE (June 2009), LILACS (May 2009) and the NIH web site (May 2009).

SELECTION CRITERIA

Randomised controlled trials (RCTs) and quasi-RCTs of heliox in infants with acute bronchiolitis.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data and assessed trial quality. We pooled data from individual trials.

MAIN RESULTS

We included four trials involving 84 infants under two years of age with respiratory distress secondary to bronchiolitis caused by respiratory syncytial virus (RSV) and requiring paediatric intensive care unit (PICU) hospitalisation. We found that infants treated with heliox inhalation had a significantly lower mean clinical respiratory score in the first hour after starting treatment when compared to those treated with air or oxygen inhalation (mean difference (MD) -1.15, 95% confidence interval (CI) -1.98 to -0.33, P = 0.006, n = 69). There was no clinically significant reduction in the rate of intubation (risk ratio (RR) 1.38, 95% CI 0.41 to 4.56, P = 0.60, n = 58), in the need for mechanical ventilation (RR 1.11, 95% CI 0.36 to 3.38, P = 0.86, n = 58), or in the length of stay in a PICU (MD = -0.15 days, 95% CI -0.92 to 0.61, P = 0.69, n = 58). No adverse events related to heliox inhalation were reported.

AUTHORS' CONCLUSIONS

Current evidence suggests that the addition of heliox therapy may significantly reduce a clinical score evaluating respiratory distress in the first hour after starting treatment in infants with acute RSV bronchiolitis. Nevertheless, there was no reduction in the rate of intubation, in the need for mechanical ventilation, or in the length of PICU stay. Further studies with homogeneous logistics in their heliox application are needed. Such studies would provide necessary information as to the appropriate place for heliox in the therapeutic schedule for severe bronchiolitis.

Paramyxovirus assembly and budding: building particles that transmit infections

The paramyxoviruses define a diverse group of enveloped RNA viruses that includes a number of important human and animal pathogens. Examples include human respiratory syncytial virus and the human parainfluenza viruses, which cause respiratory illnesses in young children and the elderly; measles and mumps viruses, which have caused recent resurgences of disease in developed countries; the zoonotic Hendra and Nipah viruses, which have caused several outbreaks of fatal disease in Australia and Asia; and Newcastle disease virus, which infects chickens and other avian species. Like other enveloped viruses, paramyxoviruses form particles that assemble and bud from cellular membranes, allowing the transmission of infections to new cells and hosts. Here, we review recent advances that have improved our understanding of events involved in paramyxovirus particle formation. Contributions of viral matrix proteins, glycoproteins, nucleocapsid proteins, and accessory proteins to particle formation are discussed, as well as the importance of host factor recruitment for efficient virus budding. Trafficking of viral structural components within infected cells is described, together with mechanisms that allow for the selection of specific sites on cellular membranes for the coalescence of viral proteins in preparation of bud formation and virion release.

Predictors of respiratory failure among previously healthy children with respiratory syncytial virus infection

BACKGROUND

Respiratory syncytial virus (RSV)-related disease is the leading cause of hospitalization among infants, with approximately 7% to 21% of these patients developing acute respiratory failure.

OBJECTIVE

The aim of this study was to identify clinical variables at initial presentation in the emergency department (ED) that may predict the subsequent need for mechanical ventilation among previously healthy, RSV-infected children who require pediatric intensive care unit (PICU) hospitalization.

STUDY DESIGN

This is a retrospective study of 67 previously healthy, RSV-infected patients admitted from January 1997 to March 2000 to the PICU. The primary outcome for this study was the need for mechanical ventilation. The relationship between clinical variables at initial ED presentation and the need for mechanical ventilation were explored using univariate and multiple logistic regression analysis.

RESULTS

On multivariate analysis, the presence of lethargy (odds ratio [OR], 12.2; P = .005), grunting (OR, 9.3; P = .01), and a Paco(2) 65 mm Hg or greater (OR, 11.8; P = .013) were clinical factors at initial presentation in the ED associated with the subsequent need for mechanical ventilation among the study cohort. A developmental model that included lethargy, grunting, and a Paco(2) of 65 mm Hg or greater performed well as a prediction model. The developmental model had a sensitivity of 71%, specificity of 96%, a positive predictive value of 86%, and a negative predictive value of 91%.

CONCLUSIONS

The presence of lethargy, grunting, and a Paco(2) of 65 mm Hg or greater at initial presentation in the ED were predictive for the subsequent need for mechanical ventilation in previously healthy, RSV-infected children admitted to the PICU.

Impact of congenital anomalies and treatment location on the outcomes of infants hospitalized with herpes simplex virus (HSV)

BACKGROUND

Herpes simplex virus (HSV) is a rare but costly reason for hospitalization in infants under 60 days of age. The impact of coexisting comorbid conditions and treatment location on hospital outcome is poorly understood.

OBJECTIVE

Determine patient and hospital factors associated with poor outcomes or death in infants hospitalized with HSV.

DESIGN

: Retrospective cohort study using the 2003 Kids' Inpatient Database (KID).

SETTING

U.S. hospitals.

PATIENTS

Infants under 60 days of age with a diagnosis of HSV.

INTERVENTION

Treatment at different types of hospitals, younger age at admission, and presence of congenital anomalies.

MEASUREMENTS

Serious complications, in-hospital death.

RESULTS

A total of 10% of the 1587 identified HSV hospitalizations had a concurrent congenital anomaly. A total of 267 infants had a serious complication and 50 died. After controlling for clinical and hospital characteristics, concurrent congenital anomalies were associated with higher odds of a serious complication (adjusted odds ratio [OR], 3.34; 95% confidence interval [CI], 2.00-5.56) and higher odds of death (adjusted OR, 4.17; 95% CI, 1.74-10.0). Similar results were found for infants admitted under 7 days of age. Although different hospital types had statistically similar clinical outcomes after controlling for case-mix differences, treatment at a children's hospital was associated with an 18% reduction in length of stay (LOS).

CONCLUSIONS

Infants with concurrent congenital anomalies infected with HSV were at increased risk for serious complications or death. Health resource use may be improved through identification and adoption of care practiced at children's hospitals.

Anti-inflammatory effect of MUC1 during respiratory syncytial virus infection of lung epithelial cells in vitro

MUC1 is a transmembrane glycoprotein expressed on the apical surface of airway epithelial cells and plays an anti-inflammatory role during airway bacterial infection. In this study, we determined whether the anti-inflammatory effect of MUC1 is also operative during the respiratory syncytial virus (RSV) infection. The lung epithelial cell line A549 was treated with RSV, and the production of TNFalpha and the levels of MUC1 protein were monitored temporally during the course of infection by ELISA and Western blot analysis. Small inhibitory RNA (siRNA) transfection was utilized to assess the role of MUC1 in regulating RSV-mediated inflammatory responses by lung epithelial cells. Our results revealed that: 1) following RSV infection, an increase in MUC1 level was preceded by an increase in TNFalpha production and completely inhibited by soluble TNF receptor (TNFR); and 2) knockdown of MUC1 using MUC1 siRNA resulted in a greater increase in TNFalpha level following RSV infection compared with control siRNA treatment. We conclude that the RSV-induced increase in the TNFalpha levels upregulates MUC1 through its interaction with TNFR, which in turn suppresses further increase in TNFalpha by RSV, thus forming a negative feedback loop in the control of RSV-induced inflammation. This is the first demonstration showing that MUC1 can suppress the virus-induced inflammatory responses.

Genomewide association analysis of respiratory syncytial virus infection in mice

Respiratory syncytial virus (RSV) is the major cause of lower respiratory tract infection in infants, with about half being infected in their first year of life. Yet only 2 to 3% of infants are hospitalized for RSV infection, suggesting that individual susceptibility contributes to disease severity. Previously, we determined that AKR/J (susceptible) mice developed high lung RSV titers and showed delayed weight recovery, whereas C57BL/6J (resistant) mice demonstrated low lung RSV titers and rapid weight recovery. In addition, we have reported that gene-targeted mice lacking the cystic fibrosis transmembrane conductance regulator (Cftr; ATP-binding cassette subfamily C, member 7) are susceptible to RSV infection. For this report, recombinant backcross and F2 progeny derived from C57BL/6J and AKR/J mice were infected with RSV, their lung titers were measured, and quantitative trait locus (QTL) analysis was performed. A major QTL, designated Rsvs1, was identified on proximal mouse chromosome 6 in both recombinant populations. Microarray analysis comparing lung transcripts of the parental strains during infection identified several candidate genes that mapped to the Rsvs1 interval, including Cftr. These findings add to our understanding of individual RSV susceptibility and strongly support a modifier role for CFTR in RSV infection, a significant cause of respiratory morbidity in infants with cystic fibrosis.

Risk factors for respiratory failure associated with respiratory syncytial virus infection in adults

Risk factors associated with respiratory failure during respiratory syncytial virus (RSV) infection have not been assessed in adults. We identified RSV by quantitative reverse transcription polymerase chain reaction in 58 adults during the 2007-2008 winter. Clinical variables and respiratory secretion viral loads were compared in 26 outpatients and 32 inpatients. Cardiopulmonary diseases were more common among inpatients than outpatients (91% vs 31%, P = .0001), whereas mean RSV load was similar. Nasal viral load was higher in ventilated vs nonventilated hospitalized patients (log(10) 3.7 +/- 1.7 plaque-forming units (PFUs)/mL vs 2.4 +/- 1.1 PFUs/mL, P = .02), and high viral load was independently associated with respiratory failure.

Vitamin D deficiency in young children with severe acute lower respiratory infection

RATIONALE

Acute lower respiratory infection (ALRI) is one of the most common reasons for hospitalization and intensive care unit admission among children. Season related decreases in the immunomodulatory molecule, vitamin D, remain an unexplored factor that might contribute to the increased occurrence of ALRI in children.

OBJECTIVE

To investigate a possible association between vitamin D deficiency and respiratory infection by comparing serum 25 hydroxyvitamin D [25(OH)D] levels in a group of young children with ALRI to an age-matched group without respiratory infection.

PATIENTS AND METHODS

Participants with a diagnosis of bronchiolitis or pneumonia (n = 55 or 50, respectively), as well as control subjects without respiratory symptoms (n = 92), were recruited at the Royal University Hospital, Saskatoon, Saskatchewan, Canada from November 2007 to May 2008. 25(OH)D levels were measured in patient serum using a competitive enzyme linked immunoassay.

RESULTS

The mean vitamin D level for the entire ALRI group was not significantly different from the control group (81 +/- 40 vs. 83 +/- 30 nmol/L, respectively). The mean vitamin D level for the ALRI subjects admitted to the pediatric intensive care unit (49 +/- 24 nmol/L) was significantly lower than that observed for both control (83 +/- 30 nmol/L) and ALRI subjects admitted to the general pediatrics ward (87 +/- 39 nmol/L). Vitamin D deficiency remained statistically related to pediatric intensive care unit admission in the multivariate analysis.

CONCLUSION

No difference was observed in vitamin D levels between the entire ALRI group and control groups; however, significantly more children admitted to the pediatric intensive care unit with ALRI were vitamin D deficient. These findings suggest that the immunomodulatory properties of vitamin D might influence ALRI disease severity.

Human respiratory syncytial virus A2 strain replicates and induces innate immune responses by respiratory epithelia of neonatal lambs

Human respiratory syncytial virus (hRSV) is a pneumovirus that causes significant respiratory disease in premature and full-term infants. It was our hypothesis that a common strain of RSV, strain A2, would infect, cause pulmonary pathology, and alter respiratory epithelial innate immune responses in neonatal lambs similarly to RSV infection in human neonates. Newborn lambs between 2 and 3 days of age were inoculated intrabronchially with RSV strain A2. The lambs were sacrificed at days 3, 6, and 14 days postinoculation. Pulmonary lesions in the 6-day postinoculation group were typical of RSV infection including bronchiolitis with neutrophils and mild peribronchiolar interstitial pneumonia. RSV mRNA and antigen were detected by qPCR and immunohistochemistry, respectively with peak mRNA levels and antigen at day 6. Expression of surfactant proteins A and D, sheep beta-defensin-1 and thyroid transcription factor-1 mRNA were also assessed by real-time qPCR. There was a significant increase in surfactant A and D mRNA expression in RSV-infected animals at day 6 postinoculation. There were no significant changes in sheep beta-defensin-1 and thyroid transcription factor-1 mRNA expression. This study shows that neonatal lambs can be infected with RSV strain A2 and the pulmonary pathology mimics that of RSV infection in human infants thereby making the neonatal lamb a useful animal model to study disease pathogenesis and therapeutics. RSV infection induces increased expression of surfactant proteins A and D in lambs, which may also be an important feature of infection in newborn infants.

Incidence and risk factors of hospitalization for bronchiolitis in preterm children: a retrospective longitudinal study in Italy

BACKGROUND

Bronchiolitis is a distressing, potentially life-threatening respiratory condition that affects infants. We evaluated the incidence and risk factors of hospitalization for broncholitis in preterm infants (i.e., a gestational age of <36 weeks) born between 2000 and 2006, and the use and impact of Palivizumab, a monoclonal antibody that in randomized clinical trials has been shown to lessen the severity of RSV-related bronchiolitis.

METHODS

Retrospective cohort study that linked data from four health administrative databases in the Lazio region (a region of central Italy): the birth register, the hospital discharge register, and two ad-hoc databases that record the doses of Palivizumab administered at two local health units.

RESULTS

Among 2407 preterm infants, 137 had at least one hospitalization for bronchiolitis in the first 18 months of life, an overall incidence rate of 4.70 per 100 person-years (95%CI: 3.98-5.56); similar incidence rates were observed by calendar year. A multiple Poisson model showed that the following characteristics were associated with higher incidence: younger age of the infant, the period between October-April, male gender, low Apgar score at birth, low birth weight, and low maternal educational level. At least one dose of Palivizumab was administered to 324 (13.5%) children; a dramatic increase from 2000 (2.8%) to 2006 (19.1%) (p < 0.01) was observed. Other factors independently associated with more frequent Palivizumab use were older maternal age, Italian-born mothers, female gender, low Apgar score, low birth weight, shorter gestational age, a diagnosis of broncho-dysplasia, and the month of birth. It is of note that none of the 34 children with congenital heart disease were prescribed Palivizumab. Performing several multiple Poisson models that also considered Palivizumab use as covariate, although the point estimates were in agreement with previous clinical trial results, we did not find in most of them a significant reduction for immunized children to be hospitalized for bronchiolitis.

CONCLUSION

In Italy the incidence of hospitalization for bronchiolitis, and its associated risk factors, are similar to that found in other countries. Although Palivizumab use is associated with the most important characteristics of severe prematurity, other aspects of its non-use in children with congenital heart disease, the age and the birth country of the mother suggest the need for public health measures that can reduce these health disparities. Finally, the estimated effectiveness of Palivizumab in routine practice, although not significant, confirms the results of previous clinical trials, but its impact on modifying the temporal trend in this population is still negligible.

Lower levels of plasmacytoid dendritic cells in peripheral blood are associated with a diagnosis of asthma 6 yr after severe respiratory syncytial virus bronchiolitis

Plasmacytoid dendritic cells (pDC) play a crucial role in antiviral immunity and promoting Th1 polarization, possibly protecting against development of allergic disease. Examination of the relationship between peripheral blood plasmacytoid DC levels and manifestations of asthma and atopy early in life. We have isolated peripheral blood mononuclear cells (PBMC) from 73 children (mean age +/- SD: 6.6 +/- 0.5 yr old) participating in the RSV Bronchiolitis in Early Life (RBEL) study. Flow cytometry was performed on PBMC detecting DC surface-markers: Blood Dendritic Cell Antigens (BDCA) 1, 3, and 2 which identify myeloid type 1, type 2, and plasmacytoid cells, respectively. Total serum IgE, peripheral eosinophil count, and allergy skin tests were documented. About 45% (n = 33) of study participants had physician-diagnosed asthma by 6 yr of age. These children had significantly lower quantities (mean +/- SD) of plasmacytoid DC than their non-asthmatic counterparts (1020 +/- 921 vs. 1952 +/- 1170 cells per 10(6) PBMC, p = 0.003). We found significantly lower numbers of myeloid dendritic cells in children with asthma (3836 +/- 2472 cells per 10(6) PBMC) compared with those without asthma (4768 +/- 2224 cells per 10(6) PBMC, p = 0.02); however, this divergence was not significant after adjusting for covariates of age, gender, race, skin test reactivity, smoke exposure, and daycare attendance. We did not identify any direct association between DC levels and markers of atopy: skin test reactivity, peripheral eosinophilia, and IgE level. Children who are diagnosed with asthma after severe RSV bronchiolitis appear to have a relative deficiency of plasmacytoid DC in peripheral blood.

Emerging genotypes of human respiratory syncytial virus subgroup A among patients in Japan

Human respiratory syncytial virus (HRSV) is a common etiological agent of acute lower respiratory tract disease in infants. We report the molecular epidemiology of HRSV in Niigata, Japan, over six successive seasons (from 2001 to 2007) and the emerging genotypes of HRSV subgroup A (HRSV-A) strains. A total of 488 HRSV samples were obtained from 1,103 screened cases in a pediatric clinic in Niigata. According to the phylogenetic analysis, among the PCR-positive samples, 338 HRSV-A strains clustered into the previously reported genotypes GA5 and GA7 and two novel genotypes, NA1 and NA2, which were genetically close to GA2 strains. One hundred fifty HRSV-B strains clustered into three genotypes, namely, GB3, SAB3, and BA, which has a 60-nucleotide insertion in the second hypervariable region of the G protein. The NA1 strains emerged first, in the 2004-2005 season, and subsequently, the NA2 strain emerged in the 2005-2006 season. Both strains caused large epidemics in the 2005-2006 and 2006-2007 seasons. The average age of children who were infected with NA2 strains was significantly higher than that of those infected with GA5 and the frequency of reinfection by NA2 was the highest among all genotypes, suggesting that this genotype possessed new antigenicity for evading past host immunity. This is the first paper to show a possible correlation between an emerging genotype, NA2, and large outbreaks of HRSV in Japan. Continuing studies to follow up the genetic changes and to clarify the mechanism of reinfection in HRSV are important steps to understand HRSV infections.

[Usefulness of different risk factor associations in predicting admissions due to respiratory syncytial virus in premature newborns of 32 to 35 weeks gestation in Spain]

AIM

The aim of the study was to evaluate the risk factor associations for respiratory syncytial virus (RSV) hospitalization in preterm infants from 32 to 35 weeks gestation, treated during two consecutive RSV seasons in Spain.

PATIENTS AND METHODS

A database (FLIP-2) was used after excluding the infants who received prophylactic palivizumab. A total of 193 RSV+ admissions and 4568 non-hospitalized children were studied. The risk factors analyzed were: chronological age <=10 weeks at start of RSV season or to be born during the first 10 weeks of the season; school-age siblings or daycare attendance; mother smoking during pregnancy; male gender; breastfeeding <=2 months; >=4 adults at home; history of wheezing; small for gestational age; >=2 smokers at home.

RESULTS

Logistic regression model included the first four previously mentioned risk factors as independently significant variables, with R(2) of 0.062 and area under curve of 0.687 (P<0.001). Predictive values for a child with the four risk factors were: sensitivity 6.2%, specificity 98.6%, predictive positive value 16.2%, negative predictive value 96.1%, accuracy 94.9%, positive likelihood ratio 4.581, and negative likelihood ratio 0.951. Positive likelihood ratio for a child with the two major risk factors is 2.657.

CONCLUSIONS

Usefulness of different risk factor associations to predict hospitalization for respiratory syncytial virus infection in preterm infants 32 to 35 weeks gestation in Spain is low, although similar to other models.

Extracellular Hsp72, an endogenous DAMP, is released by virally infected airway epithelial cells and activates neutrophils via Toll-like receptor (TLR)-4

Background

Neutrophils play an important role in the pathophysiology of RSV, though RSV does not appear to directly activate neutrophils in the lower airways. Therefore locally produced cytokines or other molecules released by virally-infected airway epithelial cells are likely responsible for recruiting and activating neutrophils. Heat shock proteins (HSPs) are generally regarded as intracellular proteins acting as molecular chaperones; however, HSP72 can also be released from cells, and the implications of this release are not fully understood.

Methods

Human bronchial epithelial cells (16HBE14o-) were infected with RSV and Hsp72 levels were measured by Western blot and ELISA. Tracheal aspirates were obtained from critically ill children infected with RSV and analyzed for Hsp72 levels by ELISA. Primary human neutrophils and differentiated HL-60 cells were cultured with Hsp72 and supernatants analyzed for cytokine production. In some cases, cells were pretreated with polymyxin B prior to treatment with Hsp72. IκBα was assessed by Western blot and EMSA's were performed to determine NF-κB activation. HL-60 cells were pretreated with neutralizing antibody against TLR4 prior to Hsp72 treatment. Neutrophils were harvested from the bone marrow of wild type or TLR4-deficient mice prior to treatment with Hsp72.

Results

Infection of 16HBE14o- with RSV showed an induction of intracellular Hsp72 levels as well as extracellular release of Hsp72. Primary human neutrophils from normal donors and differentiated HL-60 cells treated with increasing concentrations of Hsp72 resulted in increased cytokine (IL-8 and TNFα) production. This effect was independent of the low levels of endotoxin in the Hsp72 preparation. Hsp72 mediated cytokine production via activation of NF-κB translocation and DNA binding. Using bone marrow-derived neutrophils from wild type and TLR4-mutant mice, we showed that Hsp72 directly activates neutrophil-derived cytokine production via the activation of TLR4.

Conclusion

Collectively these data suggest that extracellular Hsp72 is released from virally infected airway epithelial cells resulting in the recruitment and activation of neutrophils.

Cold oxygen plasma technology efficiency against different airborne respiratory viruses

BACKGROUND

Respiratory infections caused by viruses are major causes of upper and lower respiratory tract infections. They account for an important mortality and morbidity worldwide. Amongst these viruses, influenza viruses and paramyxoviruses are major pathogens. Their transmission is mainly airborne, by direct transmission through droplets from infected cases.

OBJECTIVES

In the context of an influenza pandemic, as well as for the reduction of nosocomial infections, systems that can reduce or control virus transmission will reduce the burden of this disease. It may also be part of the strategy for pandemic mitigation.

STUDY DESIGN

A new system based on physical decontamination of surface and air has been developed. This process generates cold oxygen plasma (COP) by subjecting air to high-energy deep-UV light. To test its efficiency, we have developed an experimental device to assess for the decontamination of nebulized respiratory viruses. High titer suspensions of influenza virus type A, human parainfluenza virus type 3 and RSV have been tested.

RESULTS

Different experimental conditions have been evaluated against these viruses. The use of COP with an internal device allowed the best results against all viruses tested. We recorded a reduction of 6.5, 3.8 and 4 log(10) TCID50/mL of the titre of the hPIV-3, RSV and influenza virus A (H5N2) suspensions.

CONCLUSIONS

The COP technology is an efficient and innovative strategy to control airborne virus dissemination. It could successfully control nosocomial diffusion of respiratory viruses in hospital setting, and could be useful for the reduction of influenza transmission in the various consultation settings implemented for the management of cases during a pandemic.

Respiratory syncytial virus: from primary care to critical care

Respiratory syncytial virus (RSV) is a common disease in pediatrics. Certain subpopulations of children are at greatest risk for serious disease. However, previously healthy children also may become critically ill. In the clinic or the intensive care unit, children with RSV pose the challenge of how to treat a disease when evidence to support therapeutic options is severely limited. Prophylaxis is an option for certain children, although many do not qualify. RSV has been implicated in continued wheezing and the subsequent development of asthma. While evidence for this implication is still being sought, researchers are working on finding new ways to treat and prevent RSV.

Descriptive epidemiological features of bronchiolitis in a population-based cohort

OBJECTIVE

The goal was to investigate the epidemiological features of incident bronchiolitis by using a population-based infant cohort.

METHODS

Outpatient and inpatient health records were used to identify incident bronchiolitis cases among 93,058 singleton infants born in the Georgia Air Basin between 1999 and 2002. Additional health-related databases were linked to provide data on sociodemographic variables, maternal characteristics, and birth outcome measures.

RESULTS

From 1999 to 2002, bronchiolitis accounted for 12,474 incident health care encounters (inpatient or outpatient contacts) during the first year of life (134.2 cases per 1000 person-years). A total of 1588 hospitalized bronchiolitis cases were identified (17.1 cases per 1000 person-years). Adjusted Cox proportional-hazard analyses for both case definitions indicated an increased risk of incident bronchiolitis in the first year of life (follow-up period: 2-12 months) for boys, infants of First Nations status, infants with older siblings, and infants living in neighborhoods with smaller proportions of maternal postsecondary education. The risk also was elevated for infants born to young mothers (<20 years of age) or mothers who did not initiate breastfeeding in the hospital. Infants with low (1500-2400 g) or very low (<1500 g) birth weight and those with congenital anomalies also had increased risk. Maternal smoking during pregnancy increased the risk of hospitalized bronchiolitis.

CONCLUSIONS

This population-based study of the epidemiological features of bronchiolitis provides evidence for intervening with high-risk infants and their families. Clinical and public health interventions are recommended for the modifiable risk factors of maternal breastfeeding and smoking and for modification of vulnerable environments where possible (eg, limiting exposure to other young children), during high-risk periods such as the first few months of life or the winter season.

Low-pH triggering of human metapneumovirus fusion: essential residues and importance in entry

Human metapneumovirus (HMPV) is a significant respiratory pathogen classified in the Pneumovirinae subfamily of the paramyxovirus family. Recently, we demonstrated that HMPV F protein-promoted cell-cell fusion is stimulated by exposure to low pH, in contrast to what is observed for other paramyxovirus F proteins. In the present study, we examined the potential role of histidine protonation in HMPV F fusion and investigated the role of low pH in HMPV viral entry. Mutagenesis of the three ectodomain histidine residues of the HMPV F protein demonstrated that the mutation of a histidine in the heptad repeat B linker domain (H435) ablated fusion activity without altering cell surface expression or proteolytic processing significantly. Modeling of the HMPV F protein revealed several basic residues surrounding this histidine residue, and the mutation of these residues also reduced fusion activity. These results suggest that electrostatic repulsion in the heptad repeat B linker region may contribute to the triggering of HMPV F. In addition, we examined the effect of inhibitors of endosomal acidification or endocytosis on the entry of a recombinant green fluorescent protein-expressing HMPV. Interestingly, chemicals that raise the pH of endocytic vesicles resulted in a 30 to 50% decrease in HMPV infection, while the inhibitors of endocytosis reduced infection by as much as 90%. These data suggest that HMPV utilizes an endocytic entry mechanism, in contrast to what has been hypothesized for most paramyxoviruses. In addition, our results indicate that HMPV uses the low pH of the endocytic pathway to enhance infectivity, though the role of low pH likely differs from classically described mechanisms.

Prevalence and clinical aspects of respiratory syncytial virus A and B groups in children seen at Hospital de Clínicas of Uberlândia, MG, Brazil

Respiratory syncytial virus (RSV) is well recognized as the most important pathogen causing acute respiratory disease in infants and young children, mainly in the form of bronchiolitis and pneumonia. Two major antigenic groups, A and B, have been identified; however, there is disagreement about the severity of the diseases caused by these two types. This study investigated a possible association between RSV groups and severity of disease. Reverse transcription-polymerase chain reaction was used to characterize 128 RSV nasopharyngeal specimens from children less than five years old experiencing acute respiratory disease. A total of 82 of 128 samples (64.1%) could be typed, and, of these, 78% were group A, and 22% were group B. Severity was measured by clinical evaluation associated with demographic factors: for RSV A-infected patients, 53.1% were hospitalized, whereas for RSV B patients, 27.8% were hospitalized (p = 0.07). Around 35.0% of the patients presented risk factors for severity (e.g., prematurity). For those without risk factors, the hospitalization occurred in 47.6% of patients infected with RSV A and in 18.2% infected with RSV B. There was a trend for RSV B infections to be milder than those of RSV A. Even though RSV A-infected patients, including cases without underlying condition and prematurity, were more likely to require hospitalization than those infected by RSV B, the disease severity could not to be attributed to the RSV groups.

Performance of indirect immunofluorescence assay, immunochromatography assay and reverse transcription-polymerase chain reaction for detecting human respiratory syncytial virus in nasopharyngeal aspirate samples

Comparison of the use of indirect immunofluorescence assay (IFA), immunochromatography assay (ICA-BD) and reverse transcription-polymerase chain reaction (RT-PCR) for detecting human respiratory syncytial virus (HRSV) in 306 nasopharyngeal aspirates samples (NPA) was performed in order to assess their analytical performance. By comparing the results obtained using ICA-BD with those using IFA, we found relative indices of 85.0% for sensitivity and 91.2% for specificity, and the positive (PPV) and negative (NPV) predictive values were 85.0% and 91.2%, respectively. The relative indices for sensitivity and specificity as well as the PPV and NPV for RT-PCR were 98.0%, 89.0%, 84.0% and 99.0%, respectively, when compared to the results of IFA. In addition, comparison of the results of ICA-BD and those of RT-PCR yielded relative indices of 79.5% for sensitivity and 95.4% for specificity, as well as PPV and NPV of 92.9% and 86.0%, respectively. Although RT-PCR has shown the best performance, the substantial agreement between the ICA-BD and IFA results suggests that ICA-BD, also in addition to being a rapid and facile assay, could be suitable as an alternative diagnostic screening for HRSV infection in children.

MAVS and MyD88 are essential for innate immunity but not cytotoxic T lymphocyte response against respiratory syncytial virus

Infection by RNA viruses is detected by the host through Toll-like receptors or RIG-I-like receptors. Toll-like receptors and RIG-I-like receptors signal through the adaptors MyD88 and MAVS, respectively, to induce type I IFNs (IFN-I) and other antiviral molecules, which are thought to be essential for activating the adaptive immune system. We investigated the role of these adaptors in innate and adaptive immune responses against respiratory syncytial virus (RSV), a common human pathogen. Deletion of Mavs abolished the induction of IFN-I and other proinflammatory cytokines by RSV. Genome-wide expression profiling in the lung showed that the vast majority of RSV-induced genes depended on MAVS. Although Myd88 deficiency did not affect most RSV-induced genes, mice lacking both adaptors harbored a higher and more prolonged viral load and exhibited more severe pulmonary disease than those lacking either adaptor alone. Surprisingly, Myd88(-/-)Mavs(-/-) mice were able to activate a subset of pulmonary dendritic cells that traffic to the draining lymph node in response to RSV. These mice subsequently mounted a normal cytotoxic T-lymphocyte response and demonstrated delayed but effective viral clearance. These results provide an example of a normal and effective adaptive immune response in the absence of innate immunity mediated by MAVS and MyD88.

CXCL10/CXCR3-mediated responses promote immunity to respiratory syncytial virus infection by augmenting dendritic cell and CD8(+) T cell efficacy

The induction of inflammatory cytokines during respiratory viral infections contributes to both disease pathogenesis and resolution. The present studies investigated the role of the chemokine CXCL10 and its specific receptor, CXCR3, in the host response to pulmonary respiratory syncytial virus (RSV) infection. Antibody-mediated neutralization of CXCL10 resulted in a significant increase in disease pathogenesis, including airway hyperresponsiveness (AHR), mucus gene expression, and impaired viral clearance. When the pulmonary cytokine levels were examined, only type I IFN and IL-12p70 were significantly reduced. These latter observations were reflected in reduced dendritic cell (DC) numbers and DC maturation in the lungs of RSV-infected mice treated with anti-CXCL10. Neutralization of the only known receptor for CXCL10, CXCR3, resulted in similar increases in pathogenic responses. When bone marrow-derived DC were incubated with CXCL10 and RSV, an up-regulation of type I IFN was observed. In addition, T lymphocytes were also examined and a significant decrease in the number of RSV M2 peptide-specific CD8(+) T cells was identified. These findings highlight a previously unappreciated role for the CXCL10:CXCR3 signaling axis in RSV-infected animals by recruiting virus-specific T cells into the lung and promoting viral clearance.

Epidemiologic, experimental, and clinical links between respiratory syncytial virus infection and asthma

Virtually all children experience respiratory syncytial virus (RSV) infection at least once during the first 2 years of life, but only a few develop bronchiolitis and more severe disease requiring hospitalization, usually in the first 6 months of life. Children who recover from RSV-induced bronchiolitis are at increased risk for the development of recurrent wheeze and asthma in later childhood. Recent studies suggest that there is an association between RSV-induced bronchiolitis and asthma within the first decade of life but that this association is not significant after age 13. Despite the considerable progress made in our understanding of several aspects of respiratory viral infections, further work needs to be done to clarify the molecular mechanisms of early interactions between virus and host cell and the role of host gene products in the infection process. This review provides a critical appraisal of the literature in epidemiology and experimental research which links RSV infection to asthma. Studies to date demonstrate that there is a significant association between RSV infection and childhood asthma and that preventing severe primary RSV infections can decrease the risk of childhood asthma.

Development and Validation of a Risk Scoring Tool to Predict Respiratory Syncytial Virus Hospitalization in Premature Infants Born at 33 through 35 Completed Weeks of Gestation

Objective. The purpose of the study was to develop and validate a clinical instrument predicting the risk of respiratory syncytial virus (RSV)-associated hospitalization (RSV-H) in premature infants born at 33 through 35 completed weeks of gestation (33— 35GA). Design. An RSV risk scoring tool (RSV-RS) was developed by entering risk factors for RSV-H, determined in a Canadian prospective study, into a multiple logistic regression model. The scoring tool was then validated externally with data from a Spanish case-control study (FLIP). The Canadian cohort comprised 1758 RSV-positive infants born 33— 35GA, of whom 66 (3.7%) had confirmed RSV-H. The FLIP data set comprised 186 (33.4%) RSV-H cases and 371 (66.7%) controls. Method. The primary outcome measure was RSV-H. The RSV-RS score was the sum of the weighted probabilities for each included risk factor multiplied by 100 and ranged from 0 to 100. Receiver operator characteristic curve analyses determined cutoff points to predict subjects at low, moderate, or high RSV-H risk. Results. The RSV-RS included 7 risk factors and cutoff scores of 0— 48, 49— 64, and 65— 100 for low-, moderate-, and high-risk subjects, respectively. For the Canadian cohort, RSV-RS sensitivity in predicting RSV-H cases was 68.2%, with 71.9% specificity. With the FLIP data set, the RSV-RS had lower accuracy (61.3% sensitivity; 65.8% specificity) but showed significant positive association with increased risk for RSV-H. Conclusion. The RSV-RS accurately identified 33— 35GA infants at increased risk for RSV-H in a Canadian cohort. External validation with Spanish case-control study data further confirmed that the scoring tool is appropriate for the estimation of RSV-H risk.

Induction of type I interferons and interferon-inducible Mx genes during respiratory syncytial virus infection and reinfection in cotton rats

Respiratory syncytial virus (RSV) is the primary cause of bronchiolitis in young children. In general, RSV is considered to be a poor inducer of type I (alpha/beta) interferons (IFNs). Measurement of active type I IFN production during infection in vivo is demanding, as multiple IFN subtypes with overlapping activities are produced. In contrast, Mx gene expression, which is tightly regulated by type I IFN expression, is easily determined. This study therefore measured Mx expression as a reliable surrogate marker of type I IFN activity during RSV infection in vivo in a cotton rat model. It was shown that expression of Mx genes was dramatically augmented in the lungs of infected animals in a dose- and virus strain-dependent manner. The expression of Mx genes in the lungs was paralleled by their induction in the nose and spleen, although in spleen no simultaneous virus gene expression was detected. Reinfection of RSV-immune animals leads to abortive virus replication in the lungs. Thus, type I IFN and Mx gene expression was triggered in reinfected animals, even though virus could not be isolated from their lungs. Furthermore, it was demonstrated that immunity to RSV wanes with time. Virus replication and Mx gene expression became more prominent with increasing intervals between primary infection and reinfection. These results highlight the role of type I IFN in modulation of the immune response to RSV.