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With the advent of the rotavirus vaccine, the causes of acute gastroenteritis in children are evolving. In this report from three sentinel U.S. sites, norovirus is identified as a leading causal organism in acute gastroenteritis in children. Norovirus-associated acute gastroenteritis is characterized by the sudden onset of intense vomiting and dehydrating diarrhea, typically lasting 1 to 3 days, with high rates of transmission to persons of all ages. 1 Norovirus is a leading etiologic pathogen implicated in severe gastroenteritis outbreaks in the United States. 2 , 3 However, the endemic burden of norovirus-associated acute gastroenteritis identified through active, laboratory-confirmed surveillance of U.S. pediatric populations has not been fully characterized. Given the substantial decline in pediatric rotavirus-associated acute gastroenteritis in the United States since the introduction of rotavirus vaccines, 4 – 8 and given recent advances in the development of candidate norovirus vaccines, . . .

Background. Routine rotavirus vaccination of US infants began in 2006. We conducted active, population-based surveillance for rotavirus gastroenteritis hospitalizations in 3 US counties to assess vaccine impact. Methods. Children <36 months old hospitalized with diarrhea and/or vomiting were enrolled from January through June each year during the period 2006—2009 and tested for rotavirus. Age-stratified rates of hospitalization for rotavirus infection were compared with corresponding vaccination coverage among a control group of children with acute respiratory illness. To assess direct and indirect benefits, vaccination coverage rates in the control group were multiplied by vaccine effectiveness estimates to calculate expected reductions in the rate of hospitalization for rotavirus infection. Rotavirus serotypes were compared across years. Results. Compared with 2006, a significant reduction in rates of hospitalization for rotavirus infection (P <.001) was observed in 2008 among all age groups. There was an 87% reduction in the 6—11-month-old age group (coverage, 77%), a 96% reduction in the 12—23-months-old age group (coverage, 46%), and a 92% reduction in the 24—35-month-old age group (coverage, 1%), which exceeded reductions expected on the basis of coverage and vaccine effectiveness estimates. Age-specific rate reductions were nearly equivalent to those expected on the basis of age-specific vaccine coverage in 2009. Predominant strains varied annually: G1P[8] (91%) in 2006; G1P[8] (45%) and G12P[8] (36%) in 2007; G1P[8] (89%) in 2008; and G3P[8] (43%), G2P[4] (34%), and G9P[8] (27%) in 2009. Conclusions. Rotavirus vaccination has dramatically decreased rates of hospitalization for rotavirus infection among children in these US counties. In 2008, reductions were prominent among both vaccine-eligible age groups and older, largely unvaccinated children; the latter likely resulted from indirect protection. Although rates among age groups eligible for vaccination remained low in 2009, indirect benefits disappeared.

Background. Rhinoviruses frequently cause the common cold but have not been considered important causes of acute respiratory hospitalizations in children. Methods. A population-based surveillance study was performed among children <5 years of age who were hospitalized with respiratory symptoms or fever and who resided within counties encompassing Nashville, Tennessee, or Rochester, New York, from October 2000 through September 2001. Data collected included questionnaires, nasal and throat swabs for viral culture and polymerase chain reaction testing, and chart review. Rates of rhinovirus-associated hospitalizations were calculated. Results. Of 592 children enrolled, 156 (26%) were rhinovirus positive, representing 4.8 (95% confidence interval [CI], 4.3–5.2) rhinovirus-associated hospitalizations/1000 children. Age-specific rates per 1000 children were 17.6 (95% CI, 14.9–20.6) for 0–5-month-olds, 6.0 (95% CI, 5.0–7.0) for 6–23-month-olds, and 2.0 (95% CI, 1.6, 2.4) for 24–59-month-olds (P<.01) Children with a history of wheezing/asthma had significantly more rhinovirusassociated hospitalizations than those without a history (25.3/1000 children [95% CI, 21.6–29.5/1000 children] vs. 3.1/1000 children [95% CI, 2.7–3.5/1000 children]). Conclusions. Rhinoviruses were associated with nearly 5 hospitalizations/1000 children <5 years of age and were highest in children with a history of wheezing/asthma.

Background. Human metapneumovirus (HMPV) is a leading cause of acute respiratory illness (ARI) in children. Population-based incidence rates and comprehensive clinical characterizations of disease have not been established. Methods. We conducted population-based prospective surveillance for 2 years in 2 US counties of HMPV infection among children <5 years old who were hospitalized with ARI or fever. Nasal and throat specimens obtained with swabs were tested for HMPV by real-time reverse-transcription polymerase chain reaction and genotyped. Results. Forty-two (3.8%) of 1104 children tested positive for HMPV. The overall annual rate of HMPVassociated hospitalizations per 1000 children <5 years old was 1.2 (95% confidence interval [CI], 0.9–1.6). This rate was highest among infants 0–5 months old (4.9 per 1000 [95% CI, 2.9–7.2]), followed by children 6–11 months old (2.9 per 1000 [95% CI, 1.4–4.7]). The annual rate of hospitalization for HMPV infection was less than that for respiratory syncytial virus infection but similar to that for influenza and parainfluenza virus 3 infection in all age groups. The mean age of children hospitalized with HMPV infection was 6 months. Bronchiolitis, pneumonia, and asthma were the most common diagnoses among children with HMPV infection. All 4 HMPV subgroups were detected during both years at both sites. HPMV infection was most prominent from March through May. Conclusion. HMPV was detected in 3.8% of children hospitalized with ARI or fever, with a population incidence similar to that of influenza virus and parainfluenza virus 3.

Annual influenza epidemics in the United States result in an average of >36,000 deaths and 114,000 hospitalizations. Influenza can spread rapidly to patients and health care personnel in health care settings after influenza is introduced by visitors, staff, or patients. Influenza outbreaks in health care facilities can have potentially devastating consequences, particularly for immunocompromised persons. Although vaccination of health care personnel and patients is the primary means to prevent and control outbreaks of influenza in health care settings, antiviral influenza medications and isolation precautions are important adjuncts. Although droplet transmission is thought to be the primary mode of influenza transmission, limited evidence is available to support the relative clinical importance of contact, droplet, and droplet nuclei (airborne) transmission of influenza. In this article, the results of studies on the modes of influenza transmission and their relevant isolation precautions are reviewed.

We compared the rates of detection of respiratory viruses by reverse-transcription polymerase chain reaction (RT-PCR) and by conventional viral culture in 668 combined nasal and throat samples from a prospective, multicenter, populationbased study of acute respiratory tract infections among hospitalized children aged <5 years. RT-PCR increased the yield of viral identification by 2-fold, compared with that of culture alone. The increased sensitivity of viral detection by RT-PCR will yield better estimates of the population burden of viral respiratory infections.

Human metapneumovirus (HMPV) was identified in 2001 as a cause of respiratory infection. In this study at three U.S. surveillance centers, HPMV was found in 6 to 7% of children (<5 years old) admitted to the hospital or seen in outpatient clinics and emergency departments. Human metapneumovirus (HMPV), a paramyxovirus discovered in 2001, is associated with acute respiratory illness among infants and children worldwide. 1 – 11 In addition, HMPV causes acute respiratory illness and results in hospitalization among older adults and persons with underlying chronic conditions, including asthma, cancer, and chronic obstructive pulmonary disease. 12 – 19 However, the seasonality of HMPV disease and its overall burden in hospitalizations and outpatient visits among young children remain poorly defined. Previously published studies have been limited by their retrospective nature, 1 – 9 the use of data collected from convenience samples over relatively short periods, and the absence of asymptomatic controls. The . . .

Human respiratory syncytial virus (HRSV) is a major cause of serious lower respiratory tract illness in infants, young children, and the elderly. To characterize the circulation patterns of HRSV strains, nucleotide sequencing of the C-terminal region of the G protein gene was performed on 34–53 isolates obtained from 5 communities during 1 epidemic year, representing distinct geographical locations in North America. Phylogenetic analysis revealed that 5–7 HRSV genotypes, including 1 or 2 predominant strains, circulated in each community. The patterns of genotypes were distinct between communities, and less diversity was seen between strains of the same genotype within than between communities. These findings are consistent with HRSV outbreaks' being community based in nature, although transmission of viruses between communities may occur. Several strains are probably introduced or circulate endemically in communities each year, and local factors—possibly immunity induced by previous years' strains—determine which strains predominate during an HRSV season.

In this report, investigators from the New Vaccine Surveillance Network, sponsored by the Centers for Disease Control and Prevention, prospectively assessed the pediatric burden of undiagnosed influenza infection in inpatient and outpatient settings. In children presenting with fever or an acute respiratory tract infection, influenza was clinically diagnosed only 28 percent of the time in the inpatient setting and 13 percent of the time in the outpatient setting. In children presenting with fever or an acute respiratory tract infection, influenza was clinically diagnosed only 28 percent of the time in the inpatient setting and 13 percent of the time in the outpatient setting. Influenza virus is an important cause of respiratory illness among children. Modeling studies suggest that children younger than two years of age have high rates of hospitalization attributable to influenza; these rates are similar to rates of hospitalization attributable to influenza among older adults. 1 , 2 However, rates of hospitalization and outpatient visits attributable to laboratory-confirmed influenza infections are not well described. In 1999, the New Vaccine Surveillance Network (NVSN), sponsored by the Centers for Disease Control and Prevention (CDC), began prospective surveillance to determine population-based rates of laboratory-confirmed influenza and to assess the effects of recommendations regarding vaccination. 3 Before 2002, . . .

Background. Respiratory syncytial virus (RSV) infection is the most common respiratory viral infection resulting in hospitalizations in infants worldwide. Illness severity is likely multifactorial; however, unlike other viral infections, both type 1 and type 2 cytokine responses have been implicated in severe disease. Methods. We measured RSV-specific cytokine responses ex vivo during primary RSV infection in the blood of 18 infants with polymerase chain reaction—confirmed RSV infection. To focus on primary RSV infection, subjects were all <9 months old. RSV-specific cytokine responses were measured at 3 time points during acute primary RSV infection and at 1 memory time point 3–6 months later. Results. RSV-specific interferon (IFN)—γ responses were detected in 10 of 18 of infants. Infants with mild disease had higher RSV-specific IFN-γ memory responses than did those with moderate or severe disease. No consistent correlations between RSV-specific IFN-γ responses and corticosteroid administration were observed. RSV-specific interleukin (IL)—4 or IL-5 responses to primary RSV infection were detectable in 5 of 18 and 8 of 15 infants, respectively. Conclusions. During primary RSV infection, many infants demonstrated RSV-specific IFN-γ responses. The strongest IL-4 and IL-5 responses were detected in 3 infants with severe disease, suggesting that type 2 responses may contribute to the pathogenesis of severe disease.