Viral respiratory infections are common in infants and can be. Viral Epidemiology and Severity of Respiratory Infections in Infants in 2009

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1 ORIGINAL STUDIES Viral Epidemiology and Severity of Respiratory Infections in Infants in 2009 A Prospective Study Carmen Laurent, MD,* Audrey E. Dugué, MS, Jacques Brouard, MD,* Delphine Nimal, MD,* Julia Dina, MD, PhD, Jean-Jacques Parienti, MD, PhD, and Astrid Vabret, MD, PhD Background: Viral respiratory infections are common in infants and can be severe. The new pandemic influenza virus H1N1v2009 was feared to cause particularly severe outcomes. Objective: This study aimed at evaluating the impact of H1N1v2009 on the viral epidemiology, the clinical presentation and the severity of respiratory infections in infants. Patients and Methods: This prospective epidemiologic study included all infants <2 years of age, both inpatients and outpatients, presenting with respiratory symptoms, from November 2009 through April 2010, at the pediatric emergency department of the University Hospital of Caen, France. A nasal swab was taken for viral detection and analyzed by immunofluorescence and, if negative, polymerase chain reaction. Severe respiratory infection was defined by a score of respiratory severity. Results: One thousand twenty-one infectious episodes with a respiratory sample met inclusion criteria. Eight hundred thirty-four samples (81.7%) were positive. The viruses with the highest incidence were the respiratory syncytial virus (34.2%), the rhinoviruses (23.9%), the coronaviruses (9.3%) and H1N1v2009 (7.7%). Of all infections, 28.6% were severe and more frequent in infants with risk factors. H1N1v2009 infections had a low risk of severe respiratory disease (odds ratios = 0.15) and hospitalization (odds ratios = 0.40) compared with the other viruses. Respiratory syncytial virus infections had a high risk of respiratory severity (odds ratios = 7.85) and were responsible for 71.4% of admissions to the intensive care unit. Conclusion: Despite the modest impact of H1N1v2009 observed in this study, further surveillance is needed to detect virological factors that may increase its severity. Key Words: respiratory syncytial virus, severity, infants, respiratory infections, influenza pandemic influenza A H1N1v2009 (Pediatr Infect Dis J 2012;31: ) Viral respiratory infections are common in infants and can be severe. The clinical presentation is not specific to the causal virus. Severe outcomes are rare and most often seen in infants Accepted for publication March 19, From the *CHU de Caen, Department of Pediatrics, Caen, France; CHU de Caen, Department of Biostatistics and Clinical Research, Caen, France; and CHU de Caen, Department of Virology, Caen, France. Supported by research unit EA 2128, CHU de Caen, Université de Caen Basse- Normandie, Medical School. The authors have no conflicts of interest or funding to disclose. Address for correspondence: Astrid Vabret, MD, PhD, CHU de Caen, Department of Virology, Avenue Georges Clemenceau, Caen, France. vabret-a@chu-caen.fr. Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal s website ( Copyright 2012 by Lippincott Williams & Wilkins ISSN: /12/ DOI: /INF.0b013e with underlying conditions. Nevertheless, in 2009, the emergence of a new influenza A virus by reassortment of porcine and avian influenza strains caused great concern regarding its potential virulence. This newly discovered virus, H1N1v2009, which set off a pandemic, was supposed to cause severe respiratory disease and has a higher rate of complications such as acute respiratory distress syndrome or pneumonia. Infants <1 year of age were considered to be particularly at risk of severe outcomes. Objective This study aimed at evaluating the impact of H1N1v2009 on the epidemiology of respiratory viruses, the clinical presentation and the severity of respiratory infections in infants, both outpatients and inpatients, during the winter of PATIENTS AND METHODS Study Population All infants <24 months of age who sought medical attention for respiratory symptoms at the pediatric emergency department of the University Hospital of Caen, Lower Normandy, France, were included, whether they were outpatients or inpatients. The study period was from November 1, 2009, to April 15, This pediatric department features 39 HDU beds and 12 intensive care unit (ICU) beds and serves a region with a general population of 671,351. Inclusion Criteria Any infant presenting to the emergency department with symptoms of respiratory infection such as rhinitis, coughing, wheezing or dyspnoea, or influenza-like illness (ILI, defined as fever and cough) was eligible for inclusion. One patient could be included several times during the study period for distinct episodes of viral infection. These had to be separated from each other by a minimum of 3 days free of symptoms. The minimum interval between 2 distinct respiratory samples was 7 days. All infants who were discharged after their consultation were included in the outpatient group and those who were hospitalized in the inpatient group. When hospitalization was necessary for any other reason than respiratory infection, the infant was excluded from the inpatient group. The initial consultation at the emergency department was included in the outpatient group if inclusion criteria were fulfilled. Definitions Rhinitis was defined as nasal congestion and/or rhinorrhea. For rhinitis to be considered as final diagnosis, signs of lower airway infection had to be absent. Laryngitis was defined as barking cough, a hoarse voice and an inspiratory stridor. Bronchitis was defined as coughing with bronchial sounds upon auscultation but without lung consolidation on the chest radiograph. Bronchiolitis was defined as a first or second episode of obstructive dyspnoea with tachypnea, wheezing and variable abnormalities of chest The Pediatric Infectious Disease Journal Volume 31, Number 8, August

2 Laurent et al The Pediatric Infectious Disease Journal Volume 31, Number 8, August 2012 auscultation. From the third episode onward, these episodes were considered as recurrent wheezing. Pneumonia was defined as a viral or bacterial infection of the lung parenchyma with a localized consolidation of parenchyma on the chest radiograph, along with fever and various respiratory symptoms. Fever was defined as a temperature of 38 C. An ILI was defined as the association of fever and cough. Acute otitis media was defined as a convex, opaque aspect of the ear drum upon otoscopy. Scores of Severity To evaluate the severity of the infection, a scoring system of respiratory severity was implemented. An infectious episode was perceived as severe if the score was >6, or if one of the following items was present: saturation of oxygen in room air 92% upon arrival, hospital stay of 5 days, necessity of oxygen therapy, admission to the ICU or probable bacterial superinfection (defined as a C-reactive protein value >100 mg/l or procalcitonine >0.5 ng/l). 1 Specific samples for the detection of bacteria such as blood cultures, expectoration, urine or cerebrospinal fluid were only collected in severe cases. Infants were considered at risk if they had a history of premature birth and/or recurrent wheezing, and/or another chronical medical condition. Data Collection Clinical symptoms and diagnoses were recorded by means of a standardized questionnaire completed by the pediatrician of the emergency department after physical examination. Age, sex, fever, respiratory symptoms, saturation in room air, symptoms of respiratory distress, general condition, gastrointestinal symptoms, C-reactive protein and radiograph results (if done), and the following diagnoses: ILI, rhinitis, laryngitis, bronchitis, bronchiolitis, recurrent wheezing or pneumonia, and complications such as acute otitis media were recorded. In addition, premature birth, asthma and chronical diseases were marked. Nasal swabs were collected from all infants by the nurses of the emergency department with their parents oral consent. If the infant was hospitalized, a second standardized questionnaire was completed by a pediatrician at the end of the hospital stay. Ethical Concerns The respiratory samples were obtained when nasal decongestion was done, which is a part of the standard care and diagnostic procedure for infants in case of a respiratory infection at the pediatric emergency department. Samples were included in the study after informed consent (by means of a letter) of the patient s parent or legal guardian. Virus Detection All respiratory specimens were tested by routine tests using direct immunofluorescence assays with monoclonal antibodies (Argene, Verniolle, France and Imagen Oxoïd, Dardilly, France). They allowed for the detection of the following 8 respiratory viruses: respiratory syncytial virus (RSV), human metapneumovirus, influenza viruses A and B (InfA and InfB), adenoviruses (AdV) and parainfluenza viruses types 1, 2 and 3 (PIV 1 3). For all samples in which no virus was detected when using the immunofluorescence test, RNA/DNA was extracted by using the automated Qiasymphony system (Qiasymphony Virus/Bacteria Mini kit, Qiagen, Courtaboeuf, France), according to the manufacturer s instructions. Specimenextracted RNA/DNA were tested in a single reaction using the multiplex polymerase chain reaction (PCR)/reverse transcription-pcr Respifinder19 assay (Pathofinder, Maastricht, the Netherlands) following the manufacturer s instructions. The Respifinder assay allows for the simultaneous detection of 15 respiratory viruses [RSVA, RSVB, InfA, InfA subtype H5N1, InfB, PIV 1 4, AdV, human rhinoviruses (hrv) and human coronaviruses (HCoV)229E, NL63 and OC43], 4 bacteria (Mycoplasma pneumoniae, Chlamydophila pneumoniae, Bordetella pertussis and Legionella pneumophila) and 1 internal amplification control. This virological diagnostic strategy was completed by a real-time reverse transcription-pcr targeting the pandemic influenza virus A H1N1v2009, which was performed in emergencies following the French national recommendations and using the assays developed by the French National Centre de Reference for pandemic flu. 2 Statistical Analysis Data were processed using EpiData version 3.1 and analyzed using the R software version The statistical tests performed were the χ 2 test (with Yates correction or Fisher s exact test), the Student s test, the analysis of variance test, the Mann-Whitney test and the Kruskal-Wallis test, depending on the variables (quantitative or qualitative), their conditions of validity and the relations studied. The Hochberg s procedure was also used to take into account the problem of multiple comparison. For all tests, the alpha error was set at 5%. Statistical significance was defined as a P-value <0.05. The intraindividual correlation was ignored in all tests. Odds ratios (ORs) were calculated comparing the risk of developing a certain complication when infected by the virus studied to that of those infected by other viruses or with no virus detected. RESULTS One thousand twenty-one nasal swabs from distinct episodes of respiratory infection in 921 infants met inclusion criteria; 345 of these episodes required hospitalization and 676 did not. Clinical data were available for 745 infectious episodes [338 hospitalizations (97.97%) and 407 outpatient consultations (60.21%)]. Of the 921 infants included, 515 (55.92%) were boys and 406 (44.08%) were girls. Of the 1021 consultations, 179 (17.53%) infants were <3 months old, 179 (17.53%) between 3 and 6 months, 258 (25.27%) between 6 and 12 months and 405 (39.67%) between 12 and 24 months old. The median age was 9.5 months. In 75 infectious episodes (10.07% of all infections with clinical data), the infants had a history of premature birth, in 83 episodes (11.14%) they had a diagnosis of recurrent wheezing and in 21 (2.82%) they had another underlying chronical medical condition. During the study period, medical attention for 840 (91.21%) infants was sought at the emergency department for a single episode of respiratory infection, for 66 (6.46%) for 2 episodes, for 11 (1.19%) for 3 and for 4 (0.43%) for 4 episodes. The comparison of the characteristics of the inpatient and the outpatient population showed that the median age of inpatients (6.63 months) was significantly younger (P < ) than that of outpatients (10.4 months). The risk of hospitalization was significantly higher in infants with a chronical medical condition (P = 0.029) than in those without risk factors. There was no significant difference found for infants with a history of premature birth (P = 0.051) nor for those with recurrent wheezing (P = 0.066, Table 1). In the 1021 nasal swabs taken, 913 viruses were detected. With our strategy of analysis, 81.68% of the samples were positive. In the 527 samples analyzed by multiplex PCR, 403 (76.47%) were positive. In 74 of these samples, a coinfection with 2 respiratory viruses was detected (14.04%). The virus with the highest overall incidence was RSV (350 cases; 34.28% of all samples), followed by hrv (244 cases; 23.90%), HCoV (95 cases; 9.30%) and H1N1v2009 (79 cases, 7.74%). PIV were responsible for 5.88% of infections, AdV for 4.31% and human metapneumovirus for 3.33%. One infection with seasonal influenza B was detected, 3 with influenza C virus, 2 with cytomegalovirus and 1 with herpes simplex viruses. No seasonal influenza A virus was detected. The comparison of the incidence of the different Lippincott Williams & Wilkins

3 The Pediatric Infectious Disease Journal Volume 31, Number 8, August 2012 Viral Respiratory Infections viruses in the inpatient and outpatient population showed that hrv were the most frequently detected viruses in outpatients (26.78% of samples). The difference between its incidence in inpatients (18.26%) and outpatients was significant (P = 0.013). RSV infections were significantly more frequent in inpatients (53.62%) than in outpatients (24.41%, P < 0.001). H1N1v2009 was detected in 9.61% of outpatients and 4.06% of inpatients (P = 0.007). In HCoV infections, the difference was not significant (10.36% of infectious episodes in outpatients and 7.25% in inpatients, P = 0.34). Virus incidence significantly varied with age: RSV infections were most frequent in infants <3 months old (P = compared with all other age groups); AdV infections were significantly more frequent in those aged 12 to 24 months (P = 0.001, Table 2). Epidemiological analysis of the respiratory viruses found that H1N1v2009 peaked in week 47/2009 (16 cases, 30.19% of positive samples of that week) and the epidemic lasted until week 52/2009. The peak incidence of RSV was observed in week 3/2010 (43 cases, 81.34%). The incidence of hrv infections was constant throughout the study period except for a peak of incidence in late March when the incidence of other respiratory viruses declined (see Fig., Supplemental Digital Content 1, The most frequent diagnosis was bronchiolitis (355 cases), followed by rhinitis (295 cases) and bronchitis (47 cases). Pneumonia was diagnosed 36 times. Otitis media was an additional finding in 10.87% of respiratory infections. Bronchiolitis was most often caused by RSV (60.85%). The association of RSV infection and bronchiolitis (or recurrent wheezing episodes) was moderate (kappa coefficient = 0.457). Rhinitis was most often caused by hrv (30.85%). There was a slight concordance between rhinitis and hrv infection (kappa = 0.124). In 70.97% of infections with H1N1v2009, an ILI was diagnosed. There was a slight association between H1N1v2009 infection and ILI (kappa coefficient = 0.132). The overall hospitalization rate was 33.79%. Fourteen infants (4.06% of those hospitalized, N = 345) required admission to the ICU. Ten of them (71.43%) were infected by RSV, and none by H1N1v2009. The respiratory severity score was high (>6) in 212 episodes of respiratory infection (28.61% of all episodes with clinical data). RSV was associated with a higher risk of hospitalization (OR = 3.58, compared with the all infectious episodes with another virus or with no virus detected) and a higher risk (OR = 7.85) of a high respiratory severity score. H1N1v2009 was associated with the lowest risk of hospitalization (OR = 0.4) and a low risk for a high respiratory severity score (OR = 0.15). Infants at risk had a significantly higher risk of hospitalization than those not at risk (OR = 1.73 versus OR = 0.63; P < ). Infants at risk had a high respiratory severity score [median score: 3, Q1 Q3 (0 5)] TABLE 1. Comparison of the Characteristics of Infectious Episodes in Outpatients and Inpatients Total Outpatients Inpatients Number of infants Number of episodes of respiratory infection N Med [Q1 Q3] N Med [Q1 Q3] P Age (in months) [ ] [ ] < Sex ratio (boys:girls) Episodes of infection N n % N n %* P Premature birth History of recurrent wheezing Other chronic medical condition *Percentages were calculated by comparing infectious episodes in children with risk factors to the total number of infections with clinical data in the respective population (outpatients N = 407 or inpatients N = 338). N is the number of infectious episodes with clinical data available (N = 407 in outpatients, N = 338 in inpatients, N = 745 overall). n is the number of infectious episodes in infants with the risk factor studied. TABLE 2. Infectious Episodes in Outpatients and Inpatients: Frequency of Detection of the Different Respiratory Viruses Outpatients Inpatients Total N Virus n % n % OR IC RSV Rhinoviruses Coronaviruses H1N1v Parainfluenza viruses Adenoviruses Metapneumovirus Positive samples Negative samples Total 676 (66.2%) 345 (33.8%) 913 The OR is the change in the risk of hospitalization if infected with the virus tested. IC is the 95% confidence interval. Percentages were calculated comparing the number of episodes of infection with the virus tested to the total number of infectious episodes included. N = 1021 was the total number of respiratory samples taken. The most frequently detected virus (overall and in inpatients) was the RSV. The rhinoviruses were the most frequently detected viruses in outpatients. H1N1v2009 was in fourth place in terms of incidence Lippincott Williams & Wilkins 829

4 Laurent et al The Pediatric Infectious Disease Journal Volume 31, Number 8, August 2012 TABLE 3. Frequency of Markers of Respiratory Severity and Their Association With the Respiratory Virus Detected Initial Saturation* 92% Respiratory Severity Score >6 n Virus n % OR IC n % OR IC RSV Rhinoviruses Coronaviruses H1N1v Parainfluenza viruses Adenoviruses Metapneumovirus Positive samples Negative samples Total 55 (7.4%) 68 (9.1%) Range of values (65 92%) (7 14) Markers of respiratory severity which were evaluated for all patients with clinical data available (338 inpatients and 407 outpatients, n = 745), out of N = 1021 infectious episodes with samples taken. *Saturation in room air upon arrival at the emergency department. Percentage out of all samples with clinical data. Range of values: maximum and minimum pathological value found. IC indicates 95% confidence interval. compared with those not at risk (median score: 0, Q1 Q3 (0 3)]. There was no increase in the hospitalization rate or the respiratory severity score of younger infants. In the samples analyzed by multiplex PCR (N = 527), those with coinfections (N = 74, 14.04%) had a higher risk of a high respiratory severity score than those with single virus infections (5 severe infections of the 51 coinfections for which it was possible to calculate the severity score; OR = 2.6). RSV was detected in 81.82% of infectious episodes with low saturation of oxygen upon arrival (OR = 8.88, compared with all infectious episodes with clinical data and another or no virus detected), in 80.36% of infectious episodes with dependency on oxygen (OR = 10.23) and in 45.41% of hospital stays longer than 5 days (OR = 3.18). However, infections with hrv and H1N1v2009 had a low risk of requirement of oxygen (OR = 0.26 and OR = 0.37, respectively) (Table 3 and Table, Supplemental Digital Content 2, Overall, 20 cases of probable bacterial superinfection were observed (2.67% of all infectious episodes with clinical data). There was no significant difference in the rates of superinfection between the different viruses. No important bacterial superinfection was diagnosed in infants infected by H1N1v2009 for whom clinical data were available. Of 50 outpatients with a confirmed H1N1v2009 infection, 14 were treated with oseltamivir (28%). In inpatients, 9 of the 14 infected with H1N1v2009 received treatment (64.3%). The overall treatment rate with oseltamivir in infants with a confirmed H1N1v2009 infection was 35.9%. DISCUSSION This prospective epidemiological study included a large number of infant consultations and respiratory specimens, for both outpatients and inpatients. There have otherwise been few studies that have analyzed the incidence of other respiratory viruses during the circulation of the pandemic influenza virus A H1N1v2009, especially in this very young population. The virological diagnostic strategy allowed for the detection of a very large spectrum of respiratory viruses by using a multiplex viral detection assay. Today, prospective cohort studies using such molecular methods are rare. However, one of the limitations of this study is found in the fact that only samples with no virus detected in the immunofluorescence test were tested by the multiplex PCR system. Therefore, the exact viral codetection rate cannot be estimated. Despite the very large spectrum of viruses detected, some were not included in the panel, such as bocavirus, coronavirus type HKU1 and some enterovirus species. The study population had no special characteristics, but there may have been a bias of selection of more severe cases than in the general population, because only infants presenting to the pediatric emergency department were included. The rate of virus detection was high (81.68%). Detection rates vary between studies due to the different sensitivity of the various techniques used. 1,3,4 The rate of coinfections in this study (14.04%) was similar to that in other studies. 4,5 The incidence of influenza A H1N1v2009 (7.74% overall and 9.61% in outpatients) in the study population was low compared with estimations of its incidence in the general population. 6 This may have been due to the young age of the patients and the bias of selection of more severe cases. 3 The frequency of infections with pandemic influenza was equivalent in the different age groups of infants which had previously been observed for seasonal influenza. 7 The peak incidence of H1N1v2009 in this study was in week 47/2009, whereas it was observed in week 49/2009 in the general population of Normandy (data not shown). Seasonal influenza A viruses were completely replaced by H1N1v2009. This tendency had been observed in other studies worldwide. 8,9 In terms of severity, H1N1v2009 was associated with a low risk of a high respiratory severity score. In this study, the rate of hospitalization of infants infected by H1N1v2009 was smaller than of that infected by other respiratory viruses. What s more, none of the infants infected by H1N1v2009 required admission to the ICU. Other studies found increased hospitalization rates and ICU admissions in infections with pandemic influenza. 6,10 However, these investigations were conducted in the general population and did not focus on infants. The viruses with the highest incidence in the study population were RSV, followed by hrv and HCoV. When taken seperately, outpatients were most frequently infected by hrv, followed by RSV, a phenomenon which has been observed by other authors. 3,11,12 Infants infected by RSV had the highest risk of a high score of respiratory severity and required hospitalization more frequently than those infected by other viruses. The high disease burden of RSV in infants, especially the very young ones (<3 months old) and those hospitalized, is well established. 1,13 18 Its peak incidence in Lippincott Williams & Wilkins

5 The Pediatric Infectious Disease Journal Volume 31, Number 8, August 2012 Viral Respiratory Infections infants in this study (week 3/2010) was observed later than in recent years. This may have been due to the arrival of H1N1v ,19 In Normandy, the peak incidence of RSV is most often observed in December (data not shown). Infections with hrv are the most frequent cause of a common cold and they have a low risk of severe outcome. 9,15 In this study, the incidence of hrv infections was rather constant from November to March. The peak incidence of hrv was observed in late March and early April, when the incidence of seasonal respiratory viruses declined. The rather high incidence of HCoV infections may have been due to the fact that the study period included the yearly epidemic peak of coronavirus infections during which their incidence reached approximately 10% of the samples tested. 20 Overall, 28.61% of respiratory infections in this study were severe, but a comparison with other studies is difficult due to the lack of a universal scoring system of severity. The interpretation of data on ICU hospitalizations is difficult as numbers were very limited: only 14 infants (4.06% of all hospitalizations) required hospitalization in the ICU; most of them were infected by RSV. There was no significant increase of respiratory severity in infants younger than 3 months. The rate of bacterial superinfection was low (2.67%), similar to that found in other studies. 7 Nevertheless, the hospitalization rate (33.79% of all infectious episodes) was very high, probably due to the young age of the study population. 3 Infants with risk factors had more severe outcomes of respiratory infection and they had a higher risk of hospitalization. 19,21 The comparison of the inpatient and outpatient population showed that the median age of inpatients was significantly younger. 19 In this study, there was no association found between a specific clinical presentation and any of the different respiratory viruses tested. The treatment rate with oseltamivir in infants with a confirmed H1N1v2009 infection was low (35,9%). In outpatients, this was due to the French government recommendations to treat only severe cases and infants with risk factors and those <1 year old. In hospitalized infants, this was probably due to the recommendation to only treat patients if oseltamivir could be started within 48 hours of symptom onset (except for severe cases), which was not always possible because patients often seek medical attention after a delay. ACKNOWLEDGMENTS The authors thank the nurses and the medical staff of the pediatrics department for their help and all parents and children for their participation. REFERENCES 1. Marguet C, Lubrano M, Gueudin M, et al. In very young infants severity of acute bronchiolitis depends on carried viruses. PLoS ONE. 2009;4:e Reijans M, Dingemans G, Klaassen CH, et al. RespiFinder: a new multiparameter test to differentially identify fifteen respiratory viruses. J Clin Microbiol. 2008;46: Casalegno JS, Ottmann M, Duchamp MB, et al. Rhinoviruses delayed the circulation of the pandemic influenza A (H1N1) 2009 virus in France. Clin Microbiol Infect. 2010;16: Regamey N, Kaiser L, Roiha HL, et al.; Swiss Paediatric Respiratory Research Group. Viral etiology of acute respiratory infections with cough in infancy: a community-based birth cohort study. Pediatr Infect Dis J. 2008;27: van der Zalm MM, van Ewijk BE, Wilbrink B, et al. Respiratory pathogens in children with and without respiratory symptoms. J Pediatr. 2009;154: , 400.e1. 6. Institut de Veille Sanitaire. Epidémie de grippe A(H1N1)2009: premiers éléments de bilan en France. Bulletin épidémiologique hebdomadaire. 2010; n : Dawood FS, Fiore A, Kamimoto L, et al. Burden of seasonal influenza hospitalization in children, United States, 2003 to J Pediatr. 2010;157: Blyth CC, Kelso A, McPhie KA, et al. The impact of the pandemic influenza A(H1N1) 2009 virus on seasonal influenza A viruses in the southern hemisphere, Euro Surveill. 2010;15:pii= Casalegno JS, Ottmann M, Bouscambert-Duchamp M, et al. Impact of the 2009 influenza A(H1N1) pandemic wave on the pattern of hibernal respiratory virus epidemics, France, Euro Surveill. 2009;15:pii Girard MP, Tam JS, Assossou OM, et al. The 2009 A (H1N1) influenza virus pandemic: a review. Vaccine. 2010;28: Kusel MM, de Klerk NH, Holt PG, et al. Role of respiratory viruses in acute upper and lower respiratory tract illness in the first year of life: a birth cohort study. Pediatr Infect Dis J. 2006;25: van der Zalm MM, Uiterwaal CS, Wilbrink B, et al. Respiratory pathogens in respiratory tract illnesses during the first year of life: a birth cohort study. Pediatr Infect Dis J. 2009;28: Antunes H, Rodrigues H, Silva N, et al. Etiology of bronchiolitis in a hospitalized pediatric population: prospective multicenter study. J Clin Virol. 2010;48: Hall CB. Respiratory syncytial virus in young children. Lancet. 2010;375: Naira H, Nokes DJ, Gessnere BD, et al. Global burden of acute lower respiratory infections due to respiratory syncytial virus in young children: a systematic review and meta-analysis. Lancet. 2010;375: Hemalatha R, Swetha GK, Seshacharyulu M, et al. Respiratory syncitial virus in children with acute respiratory infections. Indian J Pediatr. 2010;77: Kaur C, Chohan S, Khare S, et al. Respiratory viruses in acute bronchiolitis in Delhi. Indian Pediatr. 2010;47: Singleton RJ, Bulkow LR, Miernyk K, et al. Viral respiratory infections in hospitalized and community control children in Alaska. J Med Virol. 2010;82: Tatochenko V, Uchaikin V, Gorelov A, et al. Epidemiology of respiratory syncytial virus in children =2 years of age hospitalized with lower respiratory tract infections in the Russian Federation: a prospective, multicenter study. Clin Epidemiol. 2010;2: Vabret A, Dina J, Gouarin S, et al. Human (non-severe acute respiratory syndrome) coronavirus infections in hospitalised children in France. J Paediatr Child Health. 2008;44: Bramley AM, Bresee J, Finelli L. Pediatric influenza. Pediatr Nurs. 2009;35: Lippincott Williams & Wilkins 831