Rehospitalization for respiratory syncytial virus infection in infants with extremely low gestational age or birthweight in Denmark

Respiratory syncytial virus associated hospitalizations in children with congenital diaphragmatic hernia

BACKGROUND

To evaluate the risk of RSV infection in infants and children with congenital diaphragmatic hernia (CDH) over two consecutive RSV seasons.

METHODS

Retrospective, single-center cohort study from southern Austria including infants with CDH born between 1993 and 2012. Infants were retrieved by searching via ICD-10 codes Q79.0 and Q79.1 and by using a local electronic database. Children were followed over 2 years of life including at least two consecutive RSV seasons (November to April). We also defined a group of hypothetical RSV infections with the following criteria: 70% of the admissions due to a respiratory infection (diagnosis of bronchiolitis and/or LRI score ≥3) during the RSV seasons over the first 2 years of life, when no test for RSV was performed.

RESULTS

Twenty-nine of 45 infants with CDH comprised the study population (6 were lost to follow-up and 10 died) of whom 9 (31%) exhibited 17 hospitalizations due to respiratory illness. Two hospitalized infants (6.9% of the study population) tested RSV positive, one during the first and the other during the second RSV season. Nine of 29 infants (31%) had documentation of palivizumab prophylaxis, none (0%) had proven RSV hospitalization compared to 1 of 20 (5%) without prophylaxis during the first RSV season (p = 0.256). Including the hypothetical cases, we calculated 0 of 9 (0%) in the palivizumab group and 4 of 20 (20%) in the group without prophylaxis (p = 0.079).

CONCLUSIONS

We found a moderate rate of proven RSV hospitalizations in infants with CDH, and palivizumab prophylaxis led to a non-significant reduction of proven and hypothesized RSV hospitalizations.

Apnea, bradycardia and desaturation spells in premature infants: impact of a protocol for the duration of 'spell-free' observation on interprovider variability and readmission rates

OBJECTIVE

To study the impact of implementing a protocol to standardize the duration of observation in preterm infants with apnea/bradycardia/desaturation spells before hospital discharge on length of stay (LOS) and readmission rates.

STUDY DESIGN

A protocol to standardize the duration of in-hospital observation for preterm infants with apnea, bradycardia and desaturation spells who were otherwise ready for discharge was implemented in December 2013. We evaluated the impact of this protocol on the LOS and readmission rates of very low birth weight infants (VLBW). Data on readmission for apnea and an apparent life-threatening event (ALTE) within 30 days of discharge were collected. The pre-implementation epoch (2011 to 2013) was compared to the post-implementation period (2014 to 2016).

RESULTS

There were 426 and 368 VLBW discharges before and after initiation of the protocol during 2011 to 2013 and 2014 to 2016, respectively. The LOS did not change with protocol implementation (66±42 vs 64±42 days before and after implementation of the protocol, respectively). Interprovider variability on the duration of observation for apneic spells (F-8.8, P=0.04) and bradycardia spells (F-17.4, P<0.001) decreased after implementation of the protocol. The readmission rate for apnea/ALTE after the protocol decreased from 12.1 to 3.4% (P=0.01).

CONCLUSION

Implementing an institutional protocol for VLBW infants to determine the duration of apnea/bradycardia/ desaturation spell-free observation period as recommended by the American Academy of Pediatrics clinical report did not prolong the LOS but effectively reduced interprovider variability and readmission rates.

Respiratory syncytial virus hospitalizations in infants of 28 weeks gestational age and less in the palivizumab era

OBJECTIVE

To obtain data on respiratory syncytial virus (RSV) associated hospitalization rates in preterm infants of 28 weeks gestational age and less in the era of palivizumab prophylaxis.

METHODS

Retrospective single-center cohort study including all preterm infants up to 28 weeks+6days gestational age and born between 2004 and 2012 at a tertiary care university hospital. Data on RSV related hospitalizations over the first two years of life covering at least two RSV seasons (November-April) were analyzed.

RESULTS

Ninety-one of 287 (32%) infants were hospitalized due to respiratory illness, and a total of 17 infants (5.9%) tested RSV positive during the first 2 years of life. Fourteen infants (4.9%) were hospitalized during the first RSV season. RSV hospitalization rate in infants with BPD was 4.5% (2/44) compared to 4.9% (12/243) without BPD. Palivizumab prophylaxis was documented in 74.6% of the infants. Infants with RSV compared to other respiratory tract infection were of younger age (6.8 vs. 9.1 months; p=0.049), had longer hospital stays (median 11 vs. 5 days; p=0.043) and more severe respiratory illness (median LRI score 3 vs. 2; p=0.043).

CONCLUSIONS

Despite palivizumab prophylaxis the burden of RSV disease and all cause respiratory illness was still remarkable in this vulnerable preterm population and mainly limited to the first season.

Defining the Risk and Associated Morbidity and Mortality of Severe Respiratory Syncytial Virus Infection Among Infants with Chronic Lung Disease

INTRODUCTION

The REGAL (RSV evidence-a geographical archive of the literature) series provide a comprehensive review of the published evidence in the field of respiratory syncytial virus (RSV) in Western countries over the last 20 years. This third publication covers the risk and burden of RSV infection in infants with chronic lung disease (CLD), formerly called bronchopulmonary dysplasia (BPD).

METHODS

A systematic review was undertaken of publications between January 1, 1995 and December 31, 2015 across PubMed, Embase, The Cochrane Library, and Clinicaltrials.gov. Studies reporting data for hospital visits/admissions for RSV infection among infants with CLD/BPD who were not prophylaxed, as well as studies reporting RSV-associated morbidity, mortality, and healthcare costs, were included. Burdens of disease data were compared with preterm infants without CLD/BPD, other high-risk groups and term infants. Study quality and strength of evidence (SOE) were graded using recognized criteria.

RESULTS

A total of 1837 studies were identified and 39 were included. CLD/BPD is a significant independent risk factor for RSV hospitalization [RSVH (odds ratio 2.2-7.2); high SOE]. Infants and young children with CLD/BPD had high RSVH rates which were generally similar in Europe, the United States, and Canada, mostly varying between 12 and 21%. Infants with CLD also had a longer length of hospital stay than other high-risk groups and term infants (high SOE). On average, infants spent 4-11 days in hospital (moderate SOE). Once hospitalized for RSV, affected children were at risk for a more severe course of disease than children with no RSVH (moderate SOE).

CONCLUSION

Severe RSV infection in infants and young children with CLD/BPD poses a significant health burden in Western countries. Further studies focussing on the burden of RSV infection in this well-recognized population at high risk for severe disease are needed to help improve outcomes and plan allocation of healthcare resources.

FUNDING

AbbVie.

Defining the Risk and Associated Morbidity and Mortality of Severe Respiratory Syncytial Virus Infection Among Preterm Infants Without Chronic Lung Disease or Congenital Heart Disease

INTRODUCTION

The REGAL (RSV Evidence-a Geographical Archive of the Literature) series provide a comprehensive review of the published evidence in the field of respiratory syncytial virus (RSV) in Western countries over the last 20 years. This second publication covers the risk and burden of RSV infection in preterm infants born at <37 weeks' gestational age (wGA) without chronic lung disease or congenital heart disease.

METHODS

A systematic review was undertaken for articles published between January 1, 1995 and December 31, 2015. Studies reporting data for hospital visits/admissions for RSV infection among preterm infants as well as studies reporting RSV-associated morbidity, mortality, and risk factors were included. Study quality and strength of evidence (SOE) were graded using recognized criteria.

RESULTS

2469 studies were identified of which 85 were included. Preterm infants, particularly those born at lower wGA, tended to have higher RSV hospitalization (RSVH) rates compared with otherwise healthy term infants (high SOE). RSVH rates ranged from ~5 per 1000 children to >100 per 1000 children with the highest rates shown in the lowest gestational age infants (high SOE). Independent risk factors associated with RSVH include: proximity of birth to the RSV season, living with school-age siblings, smoking of mother during pregnancy or infant exposure to environmental smoking, reduced breast feeding, male sex, and familial atopy (asthma) (high SOE). Predictive models can identify 32/33-35 wGA infants at risk of RSVH (high SOE).

CONCLUSION

RSV infection remains a major burden on Western healthcare systems and is associated with significant morbidity. Further studies focusing on the prevalence and burden of RSV in different gestational age cohorts, the changing risk of RSVH during the first year of life, and on RSV-related mortality in preterm infants are needed to determine the true burden of disease.

FUNDING

AbbVie.

Neonatal hyperoxia leads to persistent alterations in NK responses to influenza A virus infection

Respiratory distress in preterm or low birth weight infants is often treated with supplemental oxygen. However, this therapy can disrupt normal lung development and architecture and alter responses to respiratory insults. Similarly, exposure of newborn mice to 100% oxygen during saccular lung development leads to permanent alveolar simplification, and upon challenge with influenza A virus, mice exhibit reduced host resistance. Natural killer (NK) cells are key players in antiviral immunity, and emerging evidence suggest they also help to maintain homeostasis in peripheral tissues, including the lung, by promoting epithelial cell regeneration via IL-22. We tested the hypothesis that adult mice exposed to hyperoxia as neonates have modified NK cell responses to infection. We report here that mice exposed to neonatal hyperoxia had fewer IL-22(+) NK cells in their lungs after influenza virus challenge and a parallel increase in IFN-γ(+) NK cells. Using reciprocal bone marrow chimeric mice, we show that exposure of either hematopoietic or nonhematopoietic cells was sufficient to increase the severity of infection and to diminish the frequency of IL-22(+) NK cells in the infected lung. Overall, our findings suggest that neonatal hyperoxia leads to long-term changes in the reparative vs. cytotoxic nature of NK cells and that this is due in part to intrinsic changes in hematopoietic cells. These differences may contribute to how oxygen alters the host response to respiratory viral infections.

Should respiratory care in preterm infants include prophylaxis against respiratory syncytial virus infection? The case in favour

Respiratory syncytial virus (RSV) is the most significant cause of acute respiratory tract infections (RTI) in infants and young children throughout the world. Preterm infants are at increased risk for severe RSV lower respiratory tract infection due to small lung volumes, a reduced lung surface area, small airways and an increased air space wall thickness. Additionally, the airways of preterm infants have been ventilated mechanically and suctioned and potentially damaged by many microtraumas with disruption of endothelial surfaces enabling pathogens to invade more easily. The immune system of preterm infants is immature resulting in low antibody titers (incomplete transplacental transfer of maternal antibodies) and a reduced cellular immunity with reduced viral clearance. Rehospitalization rates of preterm compared to term infants due to RSV infection are increased as are total morbidity and mortality associated with RSV disease. Palivizumab effectively reduces RSV related rehospitalisation in this high-risk population.

The risk of mortality among young children hospitalized for severe respiratory syncytial virus infection

Respiratory syncytial virus (RSV) lower respiratory tract infection (LRTI) is the leading cause of childhood morbidity. Although also an important cause of childhood mortality worldwide, the impact of key risk factors has not been established. A systematic review of 34 articles reporting case fatality rates in young children hospitalized for severe RSV LRTI, according to the presence of underlying RSV risk factors, was conducted. The weighted mean case fatality rate was 1.2% (range, 0-8.3%; median, 0%; n = 10) among preterm infants; 5.2% (range, 2.0-37.0%; median, 5.9%; n = 7) among children with CHD; and 4.1% (range, 0-10.5%; median, 7.0%; n = 6) among children with BPD. Case fatality estimates among children not at high risk (n = 6) ranged from 0% to 1.5% (weighted mean, 0.2%; median, 0.0%). Fatality during hospitalization for severe RSV LRTI is rare among children not at high risk, but occurs more commonly among children at higher risk of RSV LRTI.

Chronic diseases, chromosomal abnormalities, and congenital malformations as risk factors for respiratory syncytial virus hospitalization: a population-based cohort study

BACKGROUND

Little is known about how chronic conditions other than prematurity, heart disease, and Down syndrome affect the risk and severity of hospitalization for respiratory syncytial virus (RSV). We assess the risk and severity of RSV hospitalization in children with chronic conditions in this register-based, population-based cohort study.

METHODS

Data on RSV tests, maternal smoking, siblings, single parenthood, mode of delivery, gestational age at birth, major surgery, asthma diagnosis, chronic conditions, and hospitalization and discharge dates were obtained from the Danish RSV database, the National Patient and Birth Registries, and the Civil Registration System.

STATISTICS

Cox regression models were used to estimate incidence rate ratios (IRRs) for RSV hospitalization between groups stratified by sex and date of birth. Duration of RSV hospitalization was analyzed in a linear regression and reported as geometric mean ratios.

RESULTS

A total of 391 983 children aged 0-23 months were included in the analysis. A total of 10,616 (2.7%) had a diagnosis for chronic disease. IRRs (95% confidence intervals) for RSV hospitalization in children with any congenital or acquired chronic condition were 2.18 (2.01-2.36) and 2.25 (1.94-2.61), respectively. Several new risk factors for RSV hospitalization, including malformations, interstitial lung disease, neuromuscular disease, liver disease, chromosomal abnormalities, congenital immunodeficiencies, and inborn errors of metabolism, were identified. Duration of RSV hospitalization was increased in many chronic conditions.

CONCLUSIONS

Chronic disease per se is an important risk factor for RSV hospitalization.

Human rhinoviruses in severe respiratory disease in very low birth weight infants

OBJECTIVES

To assess incidence, burden of illness, and risk factors for human rhinoviruses (HRVs) in a cohort of very low birth weight (VLBW) infants.

METHODS

A 2-year prospective cohort study was conducted among VLBW premature infants in Buenos Aires, Argentina. Infants were enrolled in the NICU from June 1, 2003, to May 31, 2005, and managed monthly and with every acute respiratory illness (ARI) during the first year of life. Nasal wash samples were obtained during every respiratory episode and tested for HRV, respiratory syncytial virus (RSV), human parainfluenza viruses, influenza viruses, and human metapneumovirus using reverse transcriptase-polymerase chain reaction.

RESULTS

Of 119 patients, 66 (55%) had HRV-associated ARIs. The incidence of HRV-associated ARI was 123 events per 100 child-years of follow-up. Of those infants experiencing an episode of bronchiolitis, 40% had HRV versus 7% with RSV. The incidence of HRV-associated bronchiolitis was 75 per 100 infant-years of follow-up. HRV was associated with 12 of 36 hospitalizations (33%), and RSV was associated with 9 of 36 hospitalizations (25%). The incidence of HRV-associated hospitalization was 12 per 100 infant-years of follow-up. The risk of HRV-associated hospitalization was higher for infants with bronchopulmonary dysplasia and those who were not breastfed.

CONCLUSIONS

HRV is an important and frequent pathogen associated with severe respiratory infections in VLBW infants. Bronchopulmonary dysplasia and the absence of breastfeeding are risk factors for hospitalization. The results of our study reveal that HRV is the predominant pathogen of respiratory infections in premature infants.

Rehospitalization in the first 2 years of life in children born preterm

AIM

Aim of the study is to investigate the frequency of and predictors for rehospitalization within the first 2 years of life among preterm infants.

METHODS

All children born before 32 weeks of gestation in Northern Tyrol between January 2003 and July 2008 were prospectively enrolled. Data on rehospitalizations were obtained from hospital admission records. The association between candidate risk factors and readmission was analysed by means of logistic regression analysis.

RESULTS

In the first and second years of life, 151 and 93 of 377 children (40.1% and 24.7%), respectively, were readmitted to one of the hospitals in Northern Tyrol. The most common causes of rehospitalization were respiratory disorders, accounting for 42.1% and 47.4% of total readmissions in the first and second years of life. Chronic lung disease (CLD), male sex and smoking in pregnancy were risk conditions relevant to readmission in the first year of life, but only CLD in the second year.

CONCLUSION

Infants born before 32 weeks of gestation have a high risk of rehospitalization with respiratory illness significantly contributing to postdischarge morbidity. Neonatal intensive care should aim to further improve respiratory health in preterm infants, and adequate follow-up services must be offered.

Epidemiology of respiratory syncytial virus infection in preterm infants

This review focuses on the burden of respiratory syncytial virus (RSV) infection in preterm infants with and without chronic lung disease (bronchopulmonary dysplasia, BPD). The year-to-year and seasonal variations in RSV activity are key aspects of RSV epidemiology, and knowledge/monitoring of local RSV activity is mandatory for guidance of prophylaxis with the monoclonal antibodies palivizumab and in the near future motavizumab. Morbidity expressed in rates of hospitalizations attributable to RSV illness revealed a mean of 10 percent in preterm infants without and 19 percent (p=0.016) with BPD. Mortality rates diverged widely, and case fatality rates have been reported to range from 0 to 12 percent. The typical clinical picture of lower respiratory tract infection is not different in term and preterm infants, but rates of apnoeas are significantly increased in preterms, ranging from 4.9 to 37.5 percent with decreasing rates observed in more recent studies. Until a RSV vaccine is developed and will be available, prophylaxis with palivizumab is the only preventative strategy other than hand hygiene and contact measures that significantly reduces RSV hospitalization rates in preterm infants both with and without BPD.

CARESS: the Canadian registry of palivizumab

BACKGROUND

Palivizumab is indicated for respiratory syncytial virus (RSV) prophylaxis in high-risk children. However, relatively little is known about the current use, compliance, and outcomes associated with this medication.

METHODS

A prospective, observational, registry based on 27 sites, with monthly follow-up of infants at high risk for RSV who received at least 1 dose of palivizumab during the 2005-2009 RSV seasons.

RESULTS

A total of 5286 children were enrolled (56.6% male; 71.7% white; average gestational age, 32.1 ± 5.5 weeks). Of them, 3741 patients (70.8%) were prophylaxed for prematurity only, 449 (8.5%) for bronchopulmonary dysplasia/chronic lung disease, 508 (9.6%) for congenital heart disease, and 588 (11.1%) for other reasons. Overall, 19,485 doses were given. On average, infants received 86.0% ± 28.4% of their expected number of injections; 71.2% of infants received their injections in the recommended time periods. Of the 5286 participants enrolled, 308 patients were hospitalized for respiratory tract illness (hospitalization rate, 5.8%). The RSV-hospitalization rate was calculated as 1.38%. Having siblings increased likelihood of hospitalization (66.9% vs. 55.7%, P < 0.005), and was significantly correlated with time to hospitalization in this cohort (P = 0.050).

CONCLUSIONS

The overall RSV-hospitalization rate in our study was within the range found in previous reports (1.3%-5.3%), although it did not mimic the declining rates of the US Palivizumab Outcomes Registry. This could be due to increased testing for RSV when hospitalized and increasing rates of prophylaxis of infants with underlying medical disorders.

[Consensus conference on acute bronchiolitis (II): epidemiology of acute bronchiolitis. Review of the scientific evidence]

A review of the evidence on epidemiology, risk factors, etiology and clinical-etiological profile of acute bronchiolitis is presented. The frequency estimates are very heterogeneous; in the population under two years the frequency of admission for bronchiolitis is between 1 and 3.5%, primary care consultations between 4 and 20% and emergency visits between 1 and 2%. The frequency of admissions for respiratory infection by respiratory syncytial virus in the risk population is: in premature infants < or =32 weeks of gestation between 4.4 and 18%, in patients with bronchopulmonary dysplasia between 7.3 and 42%, and in infants with congenital heart disease between 1.6 and 9.8%. The main risk factors are: prematurity, chronic lung disease or bronchopulmonary dysplasia, congenital heart disease and age less than 3-6 months at onset of the epidemic. Other factors are: older siblings or day care attendance, male gender, exposure to smoking, breastfeeding for less than 1-2 months and variables associated with lower socioeconomic status. Respiratory syncytial virus is the dominant etiological agent, constituting just over half the cases (median 56%; interval 27% to 73%). Other viruses implicated, in descending order of frequency, are rhinovirus, adenovirus, metapneumovirus, influenza viruses, parainfluenza, enterovirus and bocavirus. In studies with genomic detection techniques, between 20 and 25% of cases the virus involved is not identified and between 9% and 27% of cases have viral co-infection. Although respiratory syncytial virus bronchiolitis shows more wheezing and retractions, longer duration of respiratory symptoms and oxygen therapy and are associated with lower use of antibiotics. This pattern is associated with the younger age of the patients and does not help us to predict the etiology. In general, the etiological identification is not useful for the management of patients. However, in young infants (<3 months) with febrile bronchiolitis in the hospital environment, conservative management may help these patients and avoid diagnostic and therapeutic procedures.

Premorbid factors and outcome associated with respiratory virus infections in a pediatric intensive care unit

OBJECTIVES

The purpose of this study was to report the clinical features and outcome of all children with a laboratory proven diagnosis of respiratory virus infection admitted to a university Pediatric Intensive Care Unit (PICU).

METHODS

Retrospective study between January 2003 and April 2007 was carried out in the PICU. Every child with a laboratory-confirmed viral infection was included.

RESULTS

54 viruses were identified in 49 children (27 M, 22 F) over a 52-month period. The three respiratory virus species, respiratory syncytial virus (RSV) (n = 17), influenza (n = 13) and parainfluenza (n = 12), accounted for 86% of these 49 cases. PICU admissions due to influenza A (n = 10) were more common than influenza B (n = 3), whereas parainfluenza type 3 (n = 7) was the commonest subtype of parainfluenza infection. Comparing these three common viruses, the mean age of children admitted with RSV was lower than with influenza or parainfluenza (1.2 years vs. 5.6 years vs. 2.4 years, P = 0.003). Pre-existing conditions such as prematurity and chronic lung disease were only present in children with RSV infection. These respiratory viruses caused both upper (croup) and lower respiratory tract diseases (bronchiolitis, pneumonia). Extrapulmonary presentations were less prevalent and included encephalitis, seizures, cardiac arrest, coexisting diabetes ketoacidosis and acute lymphoblastic leukemia. One patient with RSV and another with influenza A died during their PICU stay. Nearly half of these patients required ventilatory support or received systemic corticosteroids, and 88% received initial broad spectrum antibiotic coverage. Approximately one in five of them had nebulised adrenaline, airway endoscopies or bacterial co-infections. Adenovirus was isolated in four patients and two (both with adenovirus type 3) died during the PICU stay.

CONCLUSIONS

In PICU, respiratory viral infections were associated with significant morbidity and life-threatening conditions.

[Recommendations for the prevention of respiratory syncytial virus infection]

Premature babies < or = 35 weeks gestation, with or without chronic lung disease (CLD), and infants affected by severe congenital heart disease should be considered high risk population for RSV infection and hospitalization. Hygienic measures and RSV monoclonal antibodies (palivizumab) have been found useful in decreasing rates of RSV hospitalization in these patients. Guidelines for their administration include: a) strongly recommended use in premature babies < or = 28 weeks gestation, or born between 29-32 weeks gestation and less than 6 months at start of RSV station or discharged along it, or affected by CLD in treatment during last 6 months or by severe congenital heart disease. Last two groups could be prophylaxed for two RSV seasons. b) Recommended use among premature babies between 32-35 weeks gestation and less than 6 months of age and presenting two or more risk factors: chronologic age < 10 weeks at start of RSV station, breastfeeding < or = 2 months (physician prescription), sibling < 14 years old, day-care assistance, family history of wheezing, > or = 4 adults at home, airways malformation or neuromuscular disease.

Réhospitalisation dans l'année suivant leur naissance des prématurés d'âge gestationnel inférieur ou égal à 32 semaines d'aménorrhée. Comparaison de 2 cohortes : 1997 et 2002

OBJECTIVE

The aim of the study was to compare the rehospitalization rate in the first year of life between 2 groups of very preterm infants born on 1997 and 2002; then we compared the very preterm infants' rehospitalization rate between our retrospective 1997 group and literature (including French cohort Epipage).

PATIENTS AND METHODS

Our retrospective study included all neonates born<or=33 GA, living in Gironde, discharged from neonatal unit at children's hospital of Bordeaux on 1997 and 2002 and rehospitalized during their first year of life.

RESULTS

Respectively 29.1% and 30.1% premature infants were rehospitalized (at least once) in 1997 and 2002 (38.2% in Epipage cohort, no statistical difference). Mean number of rehospitalizations was 1.66 in 1997 and 1.77 in 2002. Mean duration of rehospitalization was 11.8 days in 1997 and 16.8 days in 2002. These data showed no statistical difference between 1997 and 2002. Respiratory disease was the first reason of rehospitalization. Several factors were correlated with an increase risk of rehospitalization: birth weight less than 1000 g, chronic lung disease and gestational age less than 28 weeks at birth (only in 2002 cohort).

CONCLUSION

Rehospitalization rate remained stable between 1997 and 2002 whereas during this period of time, the gravity of these preterm infants had increased. The use of specific hospital discharge procedure represents a real benefit for premature infants. It must be continued after the discharge with the establishment of a strong network with the implication of parents, infants, hospital and city health workers. It may contribute to limit the very premature babies' rehospitalization rate.

Palivizumab: a review of its use as prophylaxis for serious respiratory syncytial virus infection

Palivizumab (Synagi) is a humanized monoclonal antibody that provides immunoprophylaxis against serious lower respiratory tract infections (LRTIs) caused by respiratory syncytial virus (RSV). RSV is the leading cause of hospitalization for LRTIs in infants, causing winter- or wet-season epidemics. In two double-blind, placebo-controlled trials, intramuscular palivizumab 15 mg/kg every 30 days for 5 months significantly reduced RSV-related hospitalizations by 55% in 1502 infants with prematurity and/or bronchopulmonary dysplasia/chronic lung disease (BPD/CLD) and by 45% in 1287 infants with hemodynamically significant congenital heart disease (HSCHD). Reductions were statistically significant versus placebo in infants with BPD/CLD, with all degrees of prematurity, and with acyanotic/other heart disease. Palivizumab was generally well tolerated, with < or =1.9% of recipients discontinuing treatment for tolerability reasons. In placebo-controlled trials, the most common potentially drug-related adverse events were fever, nervousness, injection-site reactions, and diarrhea. Drug-related events occurred in 7.2-11% of palivizumab recipients in controlled trials (vs 6.9-10% with placebo) and 0-7.9% in open-label trials. Very few serious potentially drug-related adverse events occurred in clinical trials; four occurred in 2 of 285 patients in one open-label trial. No significant anti-palivizumab antibodies developed during palivizumab use. Palivizumab trough serum concentrations were below the recommended 40 microg/mL in about 33% and up to 14% of children prior to their second and third palivizumab injections. In pharmacoeconomic studies, the cost of palivizumab per hospitalization averted was generally lowest in the highest-risk infants. Drug cost was generally the most influential factor in sensitivity analyses. In conclusion, prophylaxis with palivizumab significantly reduces the incidence of RSV-related hospitalization relative to placebo and is generally well tolerated in high-risk infants aged <2 years, including those with prematurity and BPD/CLD or HSCHD, which are risk factors for early or serious RSV infection. Palivizumab is approved for use in these patients. Other high-risk infants in whom palivizumab has not been formally assessed, such as those with immunodeficiency, cystic fibrosis, or location-specific risk factors (including extended hospital stays) might potentially benefit from palivizumab. The use of palivizumab in these other high-risk populations is likely to be determined as much by pharmacoeconomic considerations as by efficacy outcomes.