Background The primary role of respiratory syncytial virus (RSV) in causing infant hospitalizations is well recognized, but the total burden of RSV infection among young children remains poorly defined. Methods We conducted prospective, population-based surveillance of acute respiratory infections among children under 5 years of age in three U.S. counties. We enrolled hospitalized children from 2000 through 2004 and children presenting as outpatients in emergency departments and pediatric offices from 2002 through 2004. RSV was detected by culture and reverse-transcriptase polymerase chain reaction. Clinical information was obtained from parents and medical records. We calculated population-based rates of hospitalization associated with RSV infection and estimated the rates of RSV-associated outpatient visits. Results Among 5067 children enrolled in the study, 919 (18%) had RSV infections. Overall, RSV was associated with 20% of hospitalizations, 18% of emergency department visits, and 15% of office visits for acute respiratory infections from November through April. Average annual hospitalization rates were 17 per 1000 children under 6 months of age and 3 per 1000 children under 5 years of age. Most of the children had no coexisting illnesses. Only prematurity and a young age were independent risk factors for hospitalization. Estimated rates of RSV-associated office visits among children under 5 years of age were three times those in emergency departments. Outpatients had moderately severe RSV-associated illness, but few of the illnesses (3%) were diagnosed as being caused by RSV. Conclusions RSV infection is associated with substantial morbidity in U.S. children in both inpatient and outpatient settings. Most children with RSV infection were previously healthy, suggesting that control strategies targeting only high-risk children will have a limited effect on the total disease burden of RSV infection.

Among young children, outpatient visits associated with influenza were 10 to 250 times as common as hospitalizations. Few influenza infections were recognized clinically.

WHAT'S KNOWN ON THIS SUBJECT: Respiratory syncytial virus (RSV) infection is a leading cause of hospitalization among infants. Most estimates of RSV hospitalization rates are imprecise, having been calculated by using retrospective discharge diagnosis data and stratified age groups no narrower than 6 to 12 months.WHAT THIS STUDY ADDS: Prospective, population-based surveillance data for infants hospitalized with laboratoryconfirmed RSV infection were combined with birth certificate information to yield more precise age-specific hospitalization rates. These data should help determine priorities for the use of existing and future RSV prophylaxis strategies. abstract BACKGROUND: Respiratory syncytial virus (RSV) infection is a leading cause of hospitalization among infants. However, estimates of the RSV hospitalization burden have varied, and precision has been limited by the use of age strata grouped in blocks of 6 to $12 months. METHODS:We analyzed data from a 5-year, prospective, population-based surveillance for young children who were hospitalized with laboratoryconfirmed (reverse-transcriptase polymerase chain reaction) RSV acute respiratory illness (ARI) during October through March 2000-2005. The total population at risk was stratified by month of age by birth certificate information to yield hospitalization rates.RESULTS: There were 559 (26%) RSV-infected children among the 2149 enrolled children hospitalized with ARI (85% of all eligible children with ARI). The average RSV hospitalization rate was 5.2 per 1000 children ,24 months old. The highest age-specific rate was in infants 1 month old (25.9 per 1000 children). Infants #2 months of age, who comprised 44% of RSV-hospitalized children, had a hospitalization rate of 17.9 per 1000 children. Most children (79%) were previously healthy. Very preterm infants (,30 weeks' gestation) accounted for only 3% of RSV cases but had RSV hospitalization rates 3 times that of term infants.CONCLUSIONS: Young infants, especially those who were 1 month old, were at greatest risk of RSV hospitalization. Four-fifths of RSVhospitalized infants were previously healthy. To substantially reduce the burden of RSV hospitalizations, effective general preventive strategies will be required for all young infants, not just those with risk factors. Pediatrics 2013;132:e341-e348 AUTHORS:

In the elderly, vaccination against influenza is associated with reductions in the risk of hospitalization for heart disease, cerebrovascular disease, and pneumonia or influenza as well as the risk of death from all causes during influenza seasons. These findings highlight the benefits of vaccination and support efforts to increase the rates of vaccination among the elderly.

This study confirms that children younger than 5 years and particularly children younger than 1 year have a high burden of hospitalization from RSV, influenza, and PIV. The enhanced use of influenza vaccine and the development of RSV and PIV vaccines have the potential to reduce markedly the pediatric morbidity from ARIs.

BACKGROUND The inpatient and outpatient burden of human metapneumovirus (HMPV) infection among young children has not been well established. METHODS We conducted prospective, population-based surveillance for acute respiratory illness or fever among inpatient and outpatient children less than 5 years of age in three U.S. counties from 2003 through 2009. Clinical and demographic data were obtained from parents and medical records, HMPV was detected by means of a reverse-transcriptase polymerase-chain-reaction assay, and population-based rates of hospitalization and estimated rates of outpatient visits associated with HMPV infection were determined. RESULTS HMPV was detected in 200 of 3490 hospitalized children (6%), 222 of 3257 children in outpatient clinics (7%), 224 of 3001 children in the emergency department (7%), and 10 of 770 asymptomatic controls (1%). Overall annual rates of hospitalization associated with HMPV infection were 1 per 1000 children less than 5 years of age, 3 per 1000 infants less than 6 months of age, and 2 per 1000 children 6 to 11 months of age. Children hospitalized with HMPV infection, as compared with those hospitalized without HMPV infection, were older and more likely to receive a diagnosis of pneumonia or asthma, to require supplemental oxygen, and to have a longer stay in the intensive care unit. The estimated annual burden of outpatient visits associated with HMPV infection was 55 clinic visits and 13 emergency department visits per 1000 children. The majority of HMPV-positive inpatient and outpatient children had no underlying medical conditions, although premature birth and asthma were more frequent among hospitalized children with HMPV infection than among those without HMPV infection. CONCLUSIONS HMPV infection is associated with a substantial burden of hospitalizations and outpatient visits among children throughout the first 5 years of life, especially during the first year. Most children with HMPV infection were previously healthy. (Funded by the Centers for Disease Control and Prevention and the National Institutes of Health.)

Overall, HRVCs were detected in 7% of children hospitalized for fever or respiratory conditions and constituted almost half of all rhinovirus-associated hospitalizations, suggesting that this novel group causes a substantial burden of pediatric disease.

Rhinoviruses were associated with nearly 5 hospitalizations/1000 children <5 years of age and were highest in children with a history of wheezing/asthma.