Viral infectivity in paediatric SARS-CoV-2 clinical samples does not vary by age.

At the start of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, there was much uncertainty about the role of children in infection and transmission dynamics. Through the course of the pandemic, it became clear that children were susceptible to SARS-CoV-2 infection, although they were experiencing a notable lack of severe disease outcomes as compared to the adult population. This trend held true with the emergence of new SARS-CoV-2 variants, even in paediatric populations that were ineligible to be vaccinated. The difference in disease outcomes has prompted questions about the virological features of SARS-CoV-2 infection in this population. In order to determine if there was any difference in the infectivity of the virus produced by children with coronavirus disease 2019 (COVID-19), we compared viral RNA levels (clinical RT-qPCR C T) and infectious virus titres from 144 SARS-CoV-2-positive clinical samples collected from children aged 0 to 18 years old. We found that age had no impact on the infectiousness of SARS-CoV-2 within our cohort, with children of all ages able to produce high levels of infectious virus.

Viral infectivity in pediatric SARS-CoV-2 clinical samples does not vary by age.

During the early months of the SARS-CoV-2 pandemic, notable uncertainty emerged regarding the role of children in transmission dynamics. With time, it became more clear that children were susceptible to infection with SARS-CoV-2, but that the vast majority of children experienced mild symptoms with lower incidence of severe disease. This pattern remained consistent despite the later emergence of SARS-CoV-2 variants, including Delta and Omicron, even among children <5 ineligible for vaccination. The relative lack of severe disease in the pediatric population raised questions regarding viral kinetics and infectivity in children versus adults. We hypothesized that unique virologic features in children could explain this apparent decrease in symptoms and transmissibility early in the pandemic.

Blastomycosis in 64 Wisconsin Children: Unanticipated Infection Risk and Severity in Urban Residents.

BACKGROUND: Blastomycosis, an endemic mycosis of immunocompetent individuals, is typically seen after exposure to waterways within rural wooded regions. It is not considered a disease of urban environments. Infection can be solely pneumonic or disseminate to skin, bone or central nervous system. Unknown factors influence disease acquisition and severity in children. METHODS: We analyzed acquisition risks and disease characteristics of blastomycosis in children seen at a tertiary care center from 1998 to 2018 to identify potential exposure sources, measure disease severity and assess the effect of race upon disease severity. RESULTS: Of 64 infected children, mean age was 12.9 years, with median time to diagnosis 38.5 days. About 72% were male, 38% resided in urban counties and 50% had typical environmental exposure. Isolated pulmonary infection occurred in 33 (52%). The remainder had evidence of dissemination to skin (N = 13), bone (N = 16; 7 clinically silent) and cranium (N = 7; 3 clinically silent). Infection was moderate/severe in 19 (30%). Two children (3%) died. About 79% of children with moderate/severe disease (P = 0.008) and 71% of urban children (P = 0.007) lacked typical environmental exposure. Comparing children from urban counties to other residences, 63% versus 5% were black (P < 0.001) and 71% versus 35% developed extrapulmonary dissemination (P = 0.006). Moderate/severe disease was seen in 7/17 (42%) black children but only 12/47 (26%) children of other races (P = 0.23). CONCLUSIONS: Blastomycosis, can be endemic in urban children in the absence of typical exposure history, have frequent, sometimes clinically silent, extrapulmonary dissemination and possibly produces more severe disease in black children.

Inhibition of Human Coronaviruses by Antimalarial Peroxides.

As the toll of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic continues, efforts are ongoing to identify new agents and repurpose safe drugs for its treatment. Antimalarial peroxides have reported antiviral and anticancer activities. Here, we evaluated the in vitro activities of artesunate (AS) and two ozonides (OZ418 and OZ277) against human α-coronavirus NL63 and ß-coronaviruses OC43 and SARS-CoV-2 in several cell lines. OZ418 had the best selectivity index (SI) in NL63-infected Vero cells and MK2 cells. The overall SI of the tested compounds was cell-type dependent. In OC43-infected human foreskin fibroblasts, AS had the best cell-associated SI, ≥17 µM, while the SI of OZ418 and OZ277 was ≥12 µM and ≥7 µM, respectively. AS did not inhibit SARS-CoV-2 in either Vero or Calu-3 cells. A comparison of OZ418 and OZ277 activity in SARS-CoV2-infected Calu-3 cells revealed similar EC50 (5.3 µM and 11.6 µM, respectively), higher than the EC50 of remdesivir (1.0 ± 0.1 µM), but the SI of OZ418 was higher than OZ277. A third ozonide, OZ439, inhibited SARS-CoV-2 efficiently in Vero cells, but compared to OZ418 in Calu-3 cells, it showed higher toxicity. Improved inhibition of SARS-CoV-2 was observed when OZ418 was used together with remdesivir. Although the EC50 of ozonides might be clinically achieved in plasma after intravenous administration, sustained virus suppression in tissues will require further considerations, including drug combination. Our work supports the potential repurposing of ozonides and calls for future in vivo models.

COVID-19 pre-procedural testing strategy and early outcomes at a large tertiary care children's hospital.

PURPOSE: With the emergence of the coronavirus disease-2019 (COVID-19) pandemic, institutions were tasked with developing individualized pre-procedural testing strategies that allowed for re-initiation of elective procedures within national and state guidelines. This report describes the experience of a single US children's hospital (Children's Wisconsin, CW) in developing a universal pre-procedural COVID-19 testing protocol and reports early outcomes. METHODS: The CW pre-procedural COVID-19 response began with the creation of a multi-disciplinary taskforce that sought to develop a strategy for universal pre-procedural COVID-19 testing which (1) maximized patient safety, (2) prevented in-hospital viral transmission, (3) conserved resources, and (4) allowed for resumption of procedural care within institutional capacity. RESULTS: Of 11,209 general anesthetics performed at CW from March 16, 2020 to October 31, 2020, 11,150 patients (99.5%) underwent pre-procedural COVID-19 testing. Overall, 1.4% of pre-procedural patients tested positive for COVID-19. By June 2020, CW was operating at near-normal procedural volume and there were no documented cases of in-hospital viral transmission. Only 0.5% of procedures were performed under augmented COVID-19 precautions (negative pressure environment and highest-level personal protective equipment). CONCLUSION: CW successfully developed a multi-disciplinary pre-procedural COVID-19 testing protocol that enabled resumption of near-normal procedural volume within three months while limiting in-hospital viral transmission and resource use.

Sequencing and analysis of globally obtained human parainfluenza viruses 1 and 3 genomes.

Human Parainfluenza viruses (HPIV) type 1 and 3 are important causes of respiratory tract infections in young children globally. HPIV infections do not confer complete protective immunity so reinfections occur throughout life. Since no effective vaccine is available for the two virus subtypes, comprehensive understanding of HPIV-1 and HPIV-3 genetic and epidemic features is important for diagnosis, prevention, and treatment of HPIV-1 and HPIV-3 infections. Relatively few whole genome sequences are available for both HPIV-1 and HPIV-3 viruses, so our study sought to provide whole genome sequences from multiple countries to further the understanding of the global diversity of HPIV at a whole-genome level. We collected HPIV-1 and HPIV-3 samples and isolates from Argentina, Australia, France, Mexico, South Africa, Switzerland, and USA from the years 2003-2011 and sequenced the genomes of 40 HPIV-1 and 75 HPIV-3 viruses with Sanger and next-generation sequencing with the Ion Torrent, Illumina, and 454 platforms. Phylogenetic analysis showed that the HPIV-1 genome is evolving at an estimated rate of 4.97 × 10-4 mutations/site/year (95% highest posterior density 4.55 × 10-4 to 5.38 × 10-4) and the HPIV-3 genome is evolving at a similar rate (3.59 × 10-4 mutations/site/year, 95% highest posterior density 3.26 × 10-4 to 3.94 × 10-4). There were multiple genetically distinct lineages of both HPIV-1 and 3 circulating on a global scale. Further surveillance and whole-genome sequencing are greatly needed to better understand the spatial dynamics of these important respiratory viruses in humans.

Establishment of a lethal aged mouse model of human respiratory syncytial virus infection.

Human respiratory syncytial virus (HRSV) infection is a significant cause of morbidity and mortality, particularly among the children and the elderly. Despite extensive efforts, there is currently no formally approved vaccine and effective antiviral options against HRSV infection are limited. The development of vaccines and antiviral strategies for HRSV was partly hampered by the lack of an efficient lethal mouse model to evaluate the efficacy of the candidate vaccines or antivirals. In this study, we established a lethal HRSV mouse model by consecutively passaging a clinical HRSV isolate, GZ08-0. GZ08-18 was isolated from mouse bronchioalveolar lavage fluids at the 50th passage of GZ08-0. Importantly, all GZ08-18-inoculated mice succumbed to the infection by day 7 post infection, whereas all GZ08-0-inoculated mice recovered from the infection. Subsequent investigations demonstrated that GZ08-18 replicated to a higher titer in mouse lungs, induced more prominent lung pathology, and resulted in higher expression levels of a number of key pro-inflammatory cytokines including IFN-γ, MIP-1α, and TNF-α in comparison to that of GZ08-0. The cyclophosphamide pretreatment rendered the mice more susceptible to a lethal outcome with less rounds of virus inoculation. Full genome sequencing revealed 17 mutations in GZ08-18, some of which might account for the dramatically increased pathogenicity over GZ08-0. In addition, by using ribavirin as a positive control, we demonstrated the potential application of this lethal mouse model as a tool in HRSV investigations. Overall, we have successfully established a practical lethal mouse model for HRSV with a mouse-adapted virus, which may facilitate future in vivo studies on the evaluation of candidate vaccines and drugs against HRSV.

Simulated Respiratory Secretion for Use in the Development of Influenza Diagnostic Assays.

Many assays have been developed for the detection of influenza virus which is an important respiratory pathogen. Development of these assays commonly involves the use of human clinical samples for validation of their performance. However, clinical samples can be difficult to obtain, deteriorate over time, and be inconsistent in composition. The goal of this study was to develop a simulated respiratory secretion (SRS) that could act as a surrogate for clinical samples. To this end, we determined the effects major respiratory secretion components (Na+, K+, Ca2+, cells, albumin IgG, IgM, and mucin) have on the performance of influenza assays including both nucleic acid amplification and rapid antigen assays. Minimal effects on the molecular assays were observed for all of the components tested, except for serum derived human IgG, which suppressed the signal of the rapid antigen assays. Using dot blots we were able to show anti-influenza nucleoprotein IgG antibodies are common in human respiratory samples. We composed a SRS that contained mid-point levels of human respiratory sample components and studied its effect compared to phosphate buffered saline and virus negative clinical sample matrix on the Veritor, Sofia, CDC RT-PCR, Simplexa, cobas Liat, and Alere i influenza assays. Our results demonstrated that a SRS can interact with a variety of test methods in a similar manner to clinical samples with a similar impact on test performance.

Sequencing and analysis of globally obtained human respiratory syncytial virus A and B genomes.

BACKGROUND: Human respiratory syncytial virus (RSV) is the leading cause of respiratory tract infections in children globally, with nearly all children experiencing at least one infection by the age of two. Partial sequencing of the attachment glycoprotein gene is conducted routinely for genotyping, but relatively few whole genome sequences are available for RSV. The goal of our study was to sequence the genomes of RSV strains collected from multiple countries to further understand the global diversity of RSV at a whole-genome level. METHODS: We collected RSV samples and isolates from Mexico, Argentina, Belgium, Italy, Germany, Australia, South Africa, and the USA from the years 1998-2010. Both Sanger and next-generation sequencing with the Illumina and 454 platforms were used to sequence the whole genomes of RSV A and B. Phylogenetic analyses were performed using the Bayesian and maximum likelihood methods of phylogenetic inference. RESULTS: We sequenced the genomes of 34 RSVA and 23 RSVB viruses. Phylogenetic analysis showed that the RSVA genome evolves at an estimated rate of 6.72 × 10(-4) substitutions/site/year (95% HPD 5.61 × 10(-4) to 7.6 × 10(-4)) and for RSVB the evolutionary rate was 7.69 × 10(-4) substitutions/site/year (95% HPD 6.81 × 10(-4) to 8.62 × 10(-4)). We found multiple clades co-circulating globally for both RSV A and B. The predominant clades were GA2 and GA5 for RSVA and BA for RSVB. CONCLUSIONS: Our analyses showed that RSV circulates on a global scale with the same predominant clades of viruses being found in countries around the world. However, the distribution of clades can change rapidly as new strains emerge. We did not observe a strong spatial structure in our trees, with the same three main clades of RSV co-circulating globally, suggesting that the evolution of RSV is not strongly regionalized.

Complete genome sequences of one human respiratory syncytial antigenic group a virus from china and its four mouse-adapted isolates.

In this study, one human respiratory syncytial antigenic group A virus (HRSV-A-GZ08-0) and its four BALB/c mouse-adapted isolates were sequenced and elucidated. Nineteen nucleotides were mutated between HRSV-A-GZ08-0 and the four mouse-adapted isolates.

Analytical reactivity of 13 commercially available rapid influenza diagnostic tests with H3N2v and recently circulating influenza viruses.

OBJECTIVES: Rapid influenza diagnostic tests (RIDTs) used widely in clinical practice are simple to use and provide results within 15 minutes; however, reported performance is variable, which causes concern when novel or variant viruses emerge. This study's goal was to assess the analytical reactivity of 13 RIDTs with recently circulating seasonal and H3N2v influenza viruses, using three different viral measures. DESIGN: Virus stocks were characterized by infectious dose (ID50 ) and nucleoprotein (NP) concentration, diluted at half-log dilutions, and tested with each RIDT and real-time RT-PCR. RESULTS: Strong correlation was observed between NP concentration and RIDT reactivity; however, only weak correlation was seen with ID50 or Ct values. Only four RIDTs detected viral NP at the lowest dilution for all influenza A viruses (IAV). Influenza A viruses not detected by more than one RIDT had lower NP levels. Of the 13 RIDTs, 9 had no significant differences in reactivity across IAV when compared to NP levels. CONCLUSIONS: Previous reports of RIDT performance typically compare reactivity based on ID50 titers, which in this study correlated only weakly with proportional amounts of viral NP in prepared virus samples. In the context of the strong correlation of RIDT reactivity with NP concentration, H3N2v was found to be as reactive as seasonal circulating IAV. While these findings may not reflect clinical performance of these RIDTs, measuring NP concentration can be useful in the future to assess comparable reactivity of available RIDTs, or to assess reactivity with newly evolving or emerging viruses.

Distribution of respiratory syncytial virus subtypes A and B among infants presenting to the emergency department with lower respiratory tract infection or apnea.

BACKGROUND: Respiratory syncytial virus (RSV), a leading viral respiratory pathogen worldwide, has 2 major subtypes, A and B. OBJECTIVE: To describe the temporal and geographic distribution and parameters of disease severity associated with RSV A and B in the United States. METHODS: A US multicenter active surveillance study was conducted in emergency departments (EDs) during 2 RSV seasons. Infants <1 year of age presenting to the ED with symptoms of lower respiratory tract infection or apnea were enrolled. RSV subtypes were detected in nasal swabs by reverse transcriptase polymerase chain reaction. RESULTS: Of 4248 patients enrolled, 4172 patients were evaluable; 32.4% of patients were positive for any RSV subtype in season 1 and 29.9% in season 2. RSV A and B were detected in each region studied. More patients presented to the ED with RSV A than with RSV B (853 [20.4%] versus 453 [10.9%], respectively); RSV A-positive patients were more likely to be admitted to the hospital or intensive care unit (47.7%, versus RSV B, 35.8%; P < 0.0001); hospitalized RSV A-positive patients were less likely to be prescribed antibiotics (32.4%, versus RSV B, 47.8%; P < 0.001). CONCLUSIONS: This is the largest epidemiologic study in EDs reporting trends in RSV subtypes. RSV subtypes A and B were documented in both seasons across all US regions studied and detected in September to May. The results of this study support suggestions from smaller studies that RSV A may be more virulent than RSV B; however, more quantitative assessments of disease severity are needed.

Genome sequencing and phylogenetic analysis of 39 human parainfluenza virus type 1 strains isolated from 1997-2010.

Thirty-nine human parainfluenza type 1 (HPIV-1) genomes were sequenced from samples collected in Milwaukee, Wisconsin from 1997-2010. Following sequencing, phylogenetic analyses of these sequences plus any publicly available HPIV-1 sequences (from GenBank) were performed. Phylogenetic analysis of the whole genomes, as well as individual genes, revealed that the current HPIV-1 viruses group into three different clades. Previous evolutionary studies of HPIV-1 in Milwaukee revealed that there were two genotypes of HPIV-1 co-circulating in 1991 (previously described as HPIV-1 genotypes C and D). The current study reveals that there are still two different HPIV-1 viruses co-circulating in Milwaukee; however, both groups of HPIV-1 viruses are derived from genotype C indicating that genotype D may no longer be in circulation in Milwaukee. Analyses of genetic diversity indicate that while most of the genome is under purifying selection some regions of the genome are more tolerant of mutation. In the 40 HPIV-1 genomes sequenced in this study, the nucleotide sequence of the L gene is the most conserved while the sequence of the P gene is the most variable. Over the entire protein coding region of the genome, 81 variable amino acid residues were observed and as with nucleotide diversity, the P protein seemed to be the most tolerant of mutation (and contains the greatest proportion of non-synonymous to synonymous substitutions) while the M protein appears to be the least tolerant of amino acid substitution.

Update on influenza diagnostics: lessons from the novel H1N1 influenza A pandemic.

The menu of diagnostic tools that can be utilized to establish a diagnosis of influenza is extensive and includes classic virology techniques as well as new and emerging methods. This review of how the various existing diagnostic methods have been utilized, first in the context of a rapidly evolving outbreak of novel influenza virus and then during the different subsequent phases and waves of the pandemic, demonstrates the unique roles, advantages, and limitations of each of these methods. Rapid antigen tests were used extensively throughout the pandemic. Recognition of the low negative predictive values of these tests is important. Private laboratories with preexisting expertise, infrastructure, and resources for rapid development, validation, and implementation of laboratory-developed assays played an unprecedented role in helping to meet the diagnostic demands during the pandemic. FDA-cleared assays remain an important element of the diagnostic armamentarium during a pandemic, and a process must be developed with the FDA to allow manufacturers to modify these assays for detection of novel strains in a timely fashion. The need and role for subtyping of influenza viruses and antiviral susceptibility testing will likely depend on qualitative (circulating subtypes and their resistance patterns) and quantitative (relative prevalence) characterization of influenza viruses circulating during future epidemics and pandemics.

Whole genome sequencing and evolutionary analysis of human respiratory syncytial virus A and B from Milwaukee, WI 1998-2010.

BACKGROUND: Respiratory Syncytial Virus (RSV) is the leading cause of lower respiratory-tract infections in infants and young children worldwide. Despite this, only six complete genome sequences of original strains have been previously published, the most recent of which dates back 35 and 26 years for RSV group A and group B respectively. METHODOLOGY/PRINCIPAL FINDINGS: We present a semi-automated sequencing method allowing for the sequencing of four RSV whole genomes simultaneously. We were able to sequence the complete coding sequences of 13 RSV A and 4 RSV B strains from Milwaukee collected from 1998-2010. Another 12 RSV A and 5 RSV B strains sequenced in this study cover the majority of the genome. All RSV A and RSV B sequences were analyzed by neighbor-joining, maximum parsimony and Bayesian phylogeny methods. Genetic diversity was high among RSV A viruses in Milwaukee including the circulation of multiple genotypes (GA1, GA2, GA5, GA7) with GA2 persisting throughout the 13 years of the study. However, RSV B genomes showed little variation with all belonging to the BA genotype. For RSV A, the same evolutionary patterns and clades were seen consistently across the whole genome including all intergenic, coding, and non-coding regions sequences. CONCLUSIONS/SIGNIFICANCE: The sequencing strategy presented in this work allows for RSV A and B genomes to be sequenced simultaneously in two working days and with a low cost. We have significantly increased the amount of genomic data that is available for both RSV A and B, providing the basic molecular characteristics of RSV strains circulating in Milwaukee over the last 13 years. This information can be used for comparative analysis with strains circulating in other communities around the world which should also help with the development of new strategies for control of RSV, specifically vaccine development and improvement of RSV diagnostics.

H1N1 hemagglutinin-inhibition seroprevalence in Emergency Department Health Care workers after the first wave of the 2009 influenza pandemic.

STUDY OBJECTIVE: The 2009 H1N1 pandemic (H1N1pdm) virus has been associated with high rates of asymptomatic infections. Existing influenza infection control policies do not address potential transmission through exposure to asymptomatic infected individuals in health care settings. We conducted a seroprevalence study of H1N1pdm infection to determine whether health care workers (HCWs) in the emergency department showed increased evidence of infection during the first wave of the pandemic than that previously reported in adults in the community. METHODS: Blood samples and demographic and clinical data were collected from eligible emergency department HCWs. Subjects' sera were tested for presence of antibodies specific for seasonal H1N1 and H1N1pdm viruses by hemagglutination-inhibition assay. RESULTS: One hundred eight subjects were enrolled, of which 20 (18.5%) were seropositive for H1N1pdm and 52 (48%) for seasonal H1N1. The median age of H1N1pdm-seropositive subjects was 32 years (range, 24-59 years). Of H1N1pdm-seropositive subjects, 35% were asymptomatic. Rates of H1N1pdm detection in HCWs (18.5%) were significantly higher than those observed previously in an identical age cohort in the community (2.6%, n = 262). CONCLUSIONS: The higher serodetection rates in adults observed in the current study suggest potentially significantly more frequent infections in HCWs than in the general population. Further investigations are needed to ascertain the relative incidence of influenza infections in HCWs and non-HCWs, to study influenza transmission by asymptomatic infected subjects and ascertain the burden of such transmission in health care settings.

Phylogeography of the spring and fall waves of the H1N1/09 pandemic influenza virus in the United States.

Spatial variation in the epidemiological patterns of successive waves of pandemic influenza virus in humans has been documented throughout the 20th century but never understood at a molecular level. However, the unprecedented intensity of sampling and whole-genome sequencing of the H1N1/09 pandemic virus now makes such an approach possible. To determine whether the spring and fall waves of the H1N1/09 influenza pandemic were associated with different epidemiological patterns, we undertook a large-scale phylogeographic analysis of viruses sampled from three localities in the United States. Analysis of genomic and epidemiological data reveals distinct spatial heterogeneities associated with the first pandemic wave, March to July 2009, in Houston, TX, Milwaukee, WI, and New York State. In Houston, no specific H1N1/09 viral lineage dominated during the spring of 2009, a period when little epidemiological activity was observed in Texas. In contrast, major pandemic outbreaks occurred at this time in Milwaukee and New York State, each dominated by a different viral lineage and resulting from strong founder effects. During the second pandemic wave, beginning in August 2009, all three U.S. localities were dominated by a single viral lineage, that which had been dominant in New York during wave 1. Hence, during this second phase of the pandemic, extensive viral migration and mixing diffused the spatially defined population structure that had characterized wave 1, amplifying the one viral lineage that had dominated early on in one of the world's largest international travel centers.

Epidemiologic Observations from Passive and Targeted Surveillance during the First Wave of the 2009 H1N1 Influenza Pandemic in Milwaukee, WI.

The first wave of the 2009 influenza H1N1 pandemic (H1N1pdm) in Milwaukee, WI has been recognized as the largest reported regional outbreak in the United States. The epidemiologic and clinical characteristics of this large first wave outbreak from April 28(th) 2009-July 25(th) 2009, studied using both passive and targeted surveillance methodologies are presented. A total of 2791 individuals with H1N1pdm infection were identified; 60 % were 5-18 years old. The 5-18 year and 0-4 year age groups had high infection (1131 and 1101 per 100,000) and hospitalization (49 and 12 per 100,000) rates respectively. Non-Hispanic blacks and Hispanics had the highest hospitalization and infection rates. In targeted surveillance, infected patients had fever (78%), cough (80%), sore throat (38%), and vomiting or diarrhea (8%). The "influenza like illness" definition captured only 68 % of infected patients. Modeling estimates that 10.3 % of Milwaukee population was infected in the first wave and 59% were asymptomatic. The distinct epidemiologic profile of H1N1pdm infections observed in the study has direct implications for predicting the burden of infection and hospitalization in the next waves of H1N1pdm. Careful consideration of demographic predictors of infection and hospitalization with H1N1pdm will be important for effective preparedness for subsequent influenza seasons.

Clinical and epidemiologic characteristics of children hospitalized with 2009 pandemic H1N1 influenza A infection.

BACKGROUND: In 2009, pandemic H1N1 influenza caused significant morbidity and mortality worldwide. We describe the clinical and epidemiologic characteristics of children and adolescents hospitalized for 2009 H1N1 infections in Milwaukee, Wisconsin from April 2009 to August 2009. METHODS: We conducted retrospective chart reviews of hospitalized patients with laboratory-confirmed 2009 H1N1 infections. Data on financial burden associated with these infections were obtained and analyzed. RESULTS: A total of 75 children hospitalized for 2009 pandemic H1N1 infections were identified; the median age was 5 years (range, 2 months-19.2 years); 56% were males; 56% were Non-Hispanic Blacks; and 75%had at least one underlying medical condition. Twenty-four percent had only upper respiratory symptoms. Bacterial coinfections occurred in 1.3%.All but one patient received antivirals, 80% of patients received antibacterials,18.6% were admitted to the intensive care unit, 6% required mechanical ventilation, 2.6% required extracorporeal membrane oxygenation,and 2.6% died. The total charges incurred for H1N1 influenza hospitalizations were $4,454,191, with individual charges being highest for children > 12 years of age. CONCLUSIONS: The majority of children with pandemic H1N1 influenza associated hospitalizations had uncomplicated illness despite the frequent presence of high-risk conditions in our patient population. Laboratory confirmed 2009 pandemic H1N1 influenza hospitalizations resulted in substantial health care and economic burden during the first wave of the pandemic in spring 2009.