Rhinovirus Detection in Symptomatic and Asymptomatic Children: Value of Host Transcriptome Analysis

Use of transcriptomics for diagnosis of infections and sepsis in children: A narrative review

AIM

The aim of this review was to summarise the most recent evidence about the use of omics-based techniques as an instrument for a more rapid and accurate characterisation of respiratory tract infections, neurological infections and sepsis in paediatrics.

METHODS

We performed a narrative review using PubMed and a set of inclusion criteria: English language articles, clinical trials, meta-analysis and reviews including only paediatric population inherited to this topic in the last 15 years.

RESULTS

The examined studies suggest that host gene expression signatures are an effective method to characterise the different types of infections, to distinguish infection from colonisation and, in some cases, to assess the severity of the disease in children.

CONCLUSIONS

'Omics-based techniques' may help to define the aetiology of infections in paediatrics, representing a useful tool to choose the most appropriate therapies and limit antibiotic resistance.

Systems immunology of transcriptional responses to viral infection identifies conserved antiviral pathways across macaques and humans

Viral pandemics and epidemics pose a significant global threat. While macaque models of viral disease are routinely used, it remains unclear how conserved antiviral responses are between macaques and humans. Therefore, we conducted a cross-species analysis of transcriptomic data from over 6,088 blood samples from macaques and humans infected with one of 31 viruses. Our findings demonstrate that irrespective of primate or viral species, there are conserved antiviral responses that are consistent across infection phase (acute, chronic, or latent) and viral genome type (DNA or RNA viruses). Leveraging longitudinal data from experimental challenges, we identify virus-specific response kinetics such as host responses to Coronaviridae and Orthomyxoviridae infections peaking 1-3 days earlier than responses to Filoviridae and Arenaviridae viral infections. Our results underscore macaque studies as a powerful tool for understanding viral pathogenesis and immune responses that translate to humans, with implications for viral therapeutic development and pandemic preparedness.

Virome Data Explorer: A web resource to longitudinally explore respiratory viral infections, their interactions with other pathogens and host transcriptomic changes in over 100 people

Viral respiratory infections are an important public health concern due to their prevalence, transmissibility, and potential to cause serious disease. Disease severity is the product of several factors beyond the presence of the infectious agent, including specific host immune responses, host genetic makeup, and bacterial coinfections. To understand these interactions within natural infections, we designed a longitudinal cohort study actively surveilling respiratory viruses over the course of 19 months (2016 to 2018) in a diverse cohort in New York City. We integrated the molecular characterization of 800+ nasopharyngeal samples with clinical data from 104 participants. Transcriptomic data enabled the identification of respiratory pathogens in nasopharyngeal samples, the characterization of markers of immune response, the identification of signatures associated with symptom severity, individual viruses, and bacterial coinfections. Specific results include a rapid restoration of baseline conditions after infection, significant transcriptomic differences between symptomatic and asymptomatic infections, and qualitatively similar responses across different viruses. We created an interactive computational resource (Virome Data Explorer) to facilitate access to the data and visualization of analytical results.

Human mRNA in saliva can correctly identify individuals harboring acute infection

The COVID-19 pandemic demonstrated the poor ability of body temperature to reliably identify SARS-CoV-2-infected individuals, an observation that has been made before in the context of other infectious diseases. While acute infection does not always cause fever, it does reliably drive host transcriptional responses as the body responds at the site of infection. These transcriptional changes can occur both in cells that are directly harboring replicating pathogens and in cells elsewhere that receive a molecular signal that infection is occurring. Here, we identify a core set of approximately 70 human genes that are together upregulated in cultured human cells infected by a broad array of viral, bacterial, and fungal pathogens. We have named these "core response" genes. In theory, transcripts from these genes could serve as biomarkers of infection in the human body, in a way that is agnostic to the specific pathogen causing infection. As such, we perform human studies to show that these infection-induced human transcripts can be measured in the saliva of people harboring different types of infections. The number of these transcripts in saliva can correctly classify infection status (whether a person harbors an infection) 91% of the time. Furthermore, in the case of SARS-CoV-2 specifically, the number of core response transcripts in saliva correctly identifies infectious individuals even when enrollees, themselves, are asymptomatic and do not know they are infected.IMPORTANCEThere are a variety of clinical and laboratory criteria available to clinicians in controlled healthcare settings to help them identify whether an infectious disease is present. However, in situations such as a new epidemic caused by an unknown infectious agent, in health screening contexts performed within communities and outside of healthcare facilities or in battlefield or potential biowarfare situations, this gets more difficult. Pathogen-agnostic methods for rapid screening and triage of large numbers of people for infection status are needed, in particular methods that might work on an easily accessible biospecimen like saliva. Here, we identify a small, core set of approximately 70 human genes whose transcripts serve as saliva-based biomarkers of infection in the human body, in a way that is agnostic to the specific pathogen causing infection.

Integrated host/microbe metagenomics enables accurate lower respiratory tract infection diagnosis in critically ill children

BACKGROUNDLower respiratory tract infection (LRTI) is a leading cause of death in children worldwide. LRTI diagnosis is challenging because noninfectious respiratory illnesses appear clinically similar and because existing microbiologic tests are often falsely negative or detect incidentally carried microbes, resulting in antimicrobial overuse and adverse outcomes. Lower airway metagenomics has the potential to detect host and microbial signatures of LRTI. Whether it can be applied at scale and in a pediatric population to enable improved diagnosis and treatment remains unclear.METHODSWe used tracheal aspirate RNA-Seq to profile host gene expression and respiratory microbiota in 261 children with acute respiratory failure. We developed a gene expression classifier for LRTI by training on patients with an established diagnosis of LRTI (n = 117) or of noninfectious respiratory failure (n = 50). We then developed a classifier that integrates the host LRTI probability, abundance of respiratory viruses, and dominance in the lung microbiome of bacteria/fungi considered pathogenic by a rules-based algorithm.RESULTSThe host classifier achieved a median AUC of 0.967 by cross-validation, driven by activation markers of T cells, alveolar macrophages, and the interferon response. The integrated classifier achieved a median AUC of 0.986 and increased the confidence of patient classifications. When applied to patients with an uncertain diagnosis (n = 94), the integrated classifier indicated LRTI in 52% of cases and nominated likely causal pathogens in 98% of those.CONCLUSIONLower airway metagenomics enables accurate LRTI diagnosis and pathogen identification in a heterogeneous cohort of critically ill children through integration of host, pathogen, and microbiome features.FUNDINGSupport for this study was provided by the Eunice Kennedy Shriver National Institute of Child Health and Human Development and the National Heart, Lung, and Blood Institute (UG1HD083171, 1R01HL124103, UG1HD049983, UG01HD049934, UG1HD083170, UG1HD050096, UG1HD63108, UG1HD083116, UG1HD083166, UG1HD049981, K23HL138461, and 5R01HL155418) as well as by the Chan Zuckerberg Biohub.

Respiratory virome profiles reflect antiviral immune responses

BACKGROUND

From early life, respiratory viruses are implicated in the development, exacerbation and persistence of respiratory conditions such as asthma. Complex dynamics between microbial communities and host immune responses shape immune maturation and homeostasis, influencing health outcomes. We evaluated the hypothesis that the respiratory virome is linked to systemic immune responses, using peripheral blood and nasopharyngeal swab samples from preschool-age children in the PreDicta cohort.

METHODS

Peripheral blood mononuclear cells from 51 children (32 asthmatics and 19 healthy controls) participating in the 2-year multinational PreDicta cohort were cultured with bacterial (Bacterial-DNA, LPS) or viral (R848, Poly:IC, RV) stimuli. Supernatants were analysed by Luminex for the presence of 22 relevant cytokines. Virome composition was obtained using untargeted high throughput sequencing of nasopharyngeal samples. The metagenomic data were used for the characterization of virome profiles and the presence of key viral families (Picornaviridae, Anelloviridae, Siphoviridae). These were correlated to cytokine secretion patterns, identified through hierarchical clustering and principal component analysis.

RESULTS

High spontaneous cytokine release was associated with increased presence of Prokaryotic virome profiles and reduced presence of Eukaryotic and Anellovirus profiles. Antibacterial responses did not correlate with specific viral families or virome profile; however, low antiviral responders had more Prokaryotic and less Eukaryotic virome profiles. Anelloviruses and Anellovirus-dominated profiles were equally distributed among immune response clusters. The presence of Picornaviridae and Siphoviridae was associated with low interferon-λ responses. Asthma or allergy did not modify these correlations.

CONCLUSION

Antiviral cytokine responses at a systemic level reflect the upper airway virome composition. Individuals with low innate interferon responses have higher abundance of Picornaviruses (mostly Rhinoviruses) and bacteriophages. Bacteriophages, particularly Siphoviridae, appear to be sensitive sensors of host antimicrobial capacity, while Anelloviruses are not correlated with TLR-induced immune responses.

Severe bronchiolitis profiling as the first step towards prevention of asthma

Bronchiolitis is the most common respiratory infection leading to hospitalization and constitutes a significant healthcare burden. The two main viral agents causing bronchiolitis, respiratory syncytial virus (RSV) and rhinovirus (RV), have distinct cytopathic, immune response, and clinical characteristics. Different approaches have been suggested for subtyping bronchiolitis based on viral etiology, atopic status, transcriptome profiles in blood, airway metabolome, lipidomic data, and airway microbiota. The highest risk of asthma at school age has been in a subgroup of bronchiolitis characterized by older age, high prevalence of RV infection, previous breathing problems, and/or eczema. Regarding solely viral etiology, RV-bronchiolitis in infancy has been linked to a nearly three times higher risk of developing asthma than RSV-bronchiolitis. Although treatment with betamimetics and systemic corticosteroids has been found ineffective in bronchiolitis overall, it can be beneficial for infants with severe RV bronchiolitis. Thus, there is a need to develop a more individualized therapeutic approach for bronchiolitis and follow-up strategies for infants at higher risk of asthma in the future perspective.

A robust host-response-based signature distinguishes bacterial and viral infections across diverse global populations

Limited sensitivity and specificity of current diagnostics lead to the erroneous prescription of antibiotics. Host-response-based diagnostics could address these challenges. However, using 4,200 samples across 69 blood transcriptome datasets from 20 countries from patients with bacterial or viral infections representing a broad spectrum of biological, clinical, and technical heterogeneity, we show current host-response-based gene signatures have lower accuracy to distinguish intracellular bacterial infections from viral infections than extracellular bacterial infections. Using these 69 datasets, we identify an 8-gene signature to distinguish intracellular or extracellular bacterial infections from viral infections with an area under the receiver operating characteristic curve (AUROC) > 0.91 (85.9% specificity and 90.2% sensitivity). In prospective cohorts from Nepal and Laos, the 8-gene classifier distinguished bacterial infections from viral infections with an AUROC of 0.94 (87.9% specificity and 91% sensitivity). The 8-gene signature meets the target product profile proposed by the World Health Organization and others for distinguishing bacterial and viral infections.

Design, optimization, and application of multiplex rRT-PCR in the detection of respiratory viruses

Viral respiratory infections are common and serious diseases. Because there is no effective treatment method or vaccine for respiratory tract infection, early diagnosis is vital to identify the pathogen so as to determine the infectivity of the patient and to quickly take measures to curb the spread of the virus, if warranted, to avoid serious public health problems. Real-time reverse transcriptase PCR (rRT-PCR), which has high sensitivity and specificity, is the best approach for early diagnosis. Among rRT-PCR methods, multiplex rRT-PCR can resolve issues arising from various types of viruses, high mutation frequency, coinfection, and low concentrations of virus. However, the design, optimization, and validation of multiplex rRT-PCR are more complicated than singleplex rRT-PCR, and comprehensive research on multiplex rRT-PCR methodology is lacking. This review summarizes recent progress in multiplex rRT-PCR methodology, outlines the principles of design, optimization and validation, and describes a scheme to help diagnostic companies to design and optimize their multiplex rRT-PCR detection panel and to assist laboratory staff to solve problems in their daily work. In addition, the analytical validity, clinical validity and clinical utility of multiplex rRT-PCR in viral respiratory tract infection diagnosis are assessed to provide theoretical guidance and useful information for physicians to understand the test results.

Recurrent Wheeze Exacerbations Following Acute Bronchiolitis-A Machine Learning Approach

Introduction: Acute bronchiolitis is one of the most common respiratory infections in infancy. Although most infants with bronchiolitis do not get hospitalized, infants with hospitalized bronchiolitis are more likely to develop wheeze exacerbations during the first years of life. The objective of this prospective cohort study was to develop machine learning models to predict incidence and persistence of wheeze exacerbations following the first hospitalized episode of acute bronchiolitis. Methods: One hundred thirty-one otherwise healthy term infants hospitalized with the first episode of bronchiolitis at a tertiary pediatric hospital in Athens, Greece, and 73 age-matched controls were recruited. All patients/controls were followed up for 3 years with 6-monthly telephone reviews. Through principal component analysis (PCA), a cluster model was used to describe main outcomes. Associations between virus type and the clusters and between virus type and other clinical characteristics and demographic data were identified. Through random forest classification, a prediction model with smallest classification error was identified. Primary outcomes included the incidence and the number of caregiver-reported wheeze exacerbations. Results: PCA identified 2 clusters of the outcome measures (Cluster 1 and Cluster 2) that were significantly associated with the number of recurrent wheeze episodes over 3-years of follow-up (Chi-Squared, p < 0.001). Cluster 1 included infants who presented higher number of wheeze exacerbations over follow-up time. Rhinovirus (RV) detection was more common in Cluster 1 and was more strongly associated with clinical severity on admission (p < 0.01). A prediction model based on virus type and clinical severity could predict Cluster 1 with an overall error 0.1145 (sensitivity 75.56% and specificity 91.86%). Conclusion: A prediction model based on virus type and clinical severity of first hospitalized episode of bronchiolitis could predict sensitively the incidence and persistence of wheeze exacerbations during a 3-year follow-up. Virus type (RV) was the strongest predictor.

Integrating central nervous system metagenomics and host response for diagnosis of tuberculosis meningitis and its mimics

The epidemiology of infectious causes of meningitis in sub-Saharan Africa is not well understood, and a common cause of meningitis in this region, Mycobacterium tuberculosis (TB), is notoriously hard to diagnose. Here we show that integrating cerebrospinal fluid (CSF) metagenomic next-generation sequencing (mNGS) with a host gene expression-based machine learning classifier (MLC) enhances diagnostic accuracy for TB meningitis (TBM) and its mimics. 368 HIV-infected Ugandan adults with subacute meningitis were prospectively enrolled. Total RNA and DNA CSF mNGS libraries were sequenced to identify meningitis pathogens. In parallel, a CSF host transcriptomic MLC to distinguish between TBM and other infections was trained and then evaluated in a blinded fashion on an independent dataset. mNGS identifies an array of infectious TBM mimics (and co-infections), including emerging, treatable, and vaccine-preventable pathogens including Wesselsbron virus, Toxoplasma gondii, Streptococcus pneumoniae, Nocardia brasiliensis, measles virus and cytomegalovirus. By leveraging the specificity of mNGS and the sensitivity of an MLC created from CSF host transcriptomes, the combined assay has high sensitivity (88.9%) and specificity (86.7%) for the detection of TBM and its many mimics. Furthermore, we achieve comparable combined assay performance at sequencing depths more amenable to performing diagnostic mNGS in low resource settings.

Tuberculous meningitis is difficult to differentiate from meningitis caused by other pathogens. Here, the authors combine metagenomics-based pathogen detection in cerebrospinal fluid with a host gene expression-based machine learning classifier for diagnosis.

Myxovirus Resistance Protein A as a Marker of Viral Cause of Illness in Children Hospitalized with an Acute Infection

A biomarker for viral infection could improve the differentiation between viral and bacterial infections and reduce antibiotic overuse. We examined blood myxovirus resistance protein A (MxA) as a biomarker for viral infections in children with an acute infection. We recruited 251 children presenting with a clinical suspicion of serious bacterial infection, determined by need for a blood bacterial culture collection, and 14 children with suspected viral infection at two pediatric emergency departments. All children were aged between 4 weeks and 16 years. We classified cases according to the viral, bacterial, or other etiology of the final diagnosis. The ability of MxA to differentiate between viral and bacterial infections was assessed. The median blood MxA levels were 467 (interquartile range, 235 to 812) μg/L in 39 children with a viral infection, 469 (178 to 827) μg/L in 103 children with viral-bacterial coinfection, 119 (68 to 227) μg/L in 75 children with bacterial infection, and 150 (101 to 212) μg/L in 26 children with bacterial infection and coincidental virus finding (P < 0.001). In a receiver operating characteristics analysis, MxA cutoff level of 256 μg/L differentiated between children with viral and bacterial infections with an area under the curve of 0.81 (95% confidence interval [CI] = 0.73 to 0.90), a sensitivity of 74.4%, and a specificity of 80.0%. In conclusion, MxA protein showed moderate accuracy as a biomarker for symptomatic viral infections in children hospitalized with an acute infection. High prevalence of viral-bacterial coinfections supports the use of MxA in combination with biomarkers of bacterial infection.

IMPORTANCE Due to the diagnostic uncertainty concerning the differentiation between viral and bacterial infections, children with viral infections are often treated with antibiotics, predisposing them to adverse effects and contributing to the emerging antibiotic resistance. Since currently available biomarkers only estimate the risk of bacterial infection, a biomarker for viral infection is needed in attempts of reducing antibiotic overuse. Blood MxA protein, which has broad antiviral activity and is rapidly induced in acute, symptomatic viral infections, is a potential biomarker for viral infection. In this diagnostic study of 265 children hospitalized because of an acute infection, blood MxA cutoff level of 256 μg/L discriminated between viral and bacterial infections with a sensitivity of 74% and specificity of 80%. MxA could improve the differential diagnostics of febrile children at the emergency department but, because of frequently detected viral-bacterial coinfections, a combination with biomarkers of bacterial infection may be needed.

Advanced Point-of-Care Testing Technologies for Human Acute Respiratory Virus Detection

The ever-growing global threats to human life caused by the human acute respiratory virus (RV) infections have cost billions of lives, created a significant economic burden, and shaped society for centuries. The timely response to emerging RVs could save human lives and reduce the medical care burden. The development of RV detection technologies is essential for potentially preventing RV pandemic and epidemics. However, commonly used detection technologies lack sensitivity, specificity, and speed, thus often failing to provide the rapid turnaround times. To address this problem, new technologies are devised to address the performance inadequacies of the traditional methods. These emerging technologies offer improvements in convenience, speed, flexibility, and portability of point-of-care test (POCT). Herein, recent developments in POCT are comprehensively reviewed for eight typical acute respiratory viruses. This review discusses the challenges and opportunities of various recognition and detection strategies and discusses these according to their detection principles, including nucleic acid amplification, optical POCT, electrochemistry, lateral flow assays, microfluidics, enzyme-linked immunosorbent assays, and microarrays. The importance of limits of detection, throughput, portability, and specificity when testing clinical samples in resource-limited settings is emphasized. Finally, the evaluation of commercial POCT kits for both essential RV diagnosis and clinical-oriented practices is included.

Detection of group A streptococcus in children with confirmed viral pharyngitis and antiviral host response

Our aim was to study the detection of group A streptococcus (GAS) with different diagnostic methods in paediatric pharyngitis patients with and without a confirmed viral infection. In this prospective observational study, throat swabs and blood samples were collected from children (age 1-16 years) presenting to the emergency department with febrile pharyngitis. A confirmed viral infection was defined as a positive virus diagnostic test (nucleic acid amplification test [NAAT] and/or serology) together with an antiviral immune response of the host demonstrated by elevated (≥ 175 µg/L) myxovirus resistance protein A (MxA) blood concentration. Testing for GAS was performed by a throat culture, by 2 rapid antigen detection tests (StrepTop and mariPOC) and by 2 NAATs (Simplexa and Illumigene). Altogether, 83 children were recruited of whom 48 had samples available for GAS testing. Confirmed viral infection was diagnosed in 30/48 (63%) children with febrile pharyngitis. Enteroviruses 11/30 (37%), adenoviruses 9/30 (30%) and rhinoviruses 9/30 (30%) were the most common viruses detected. GAS was detected by throat culture in 5/30 (17%) with and in 6/18 (33%) patients without a confirmed viral infection. Respectively, GAS was detected in 4/30 (13%) and 6/18 (33%) by StrepTop, 13/30 (43%) and 10/18 (56%) by mariPOC, 6/30 (20%) and 9/18 (50%) by Simplexa, and 5/30 (17%) and 6/18 (30%) patients by Illumigene.

CONCLUSION

GAS was frequently detected also in paediatric pharyngitis patients with a confirmed viral infection. The presence of antiviral host response and increased GAS detection by sensitive methods suggest incidental throat carriage of GAS in viral pharyngitis.

WHAT IS KNOWN

•The frequency and significance of GAS-virus co-detection are poorly characterised in children with pharyngitis. •Detection of a virus and the antiviral host response likely indicates symptomatic infection.

WHAT IS NEW

•Group A streptococcus (GAS) was detected in 17-43% of the children with confirmed viral pharyngitis depending on the GAS diagnostic method. •Our results emphasize the risk of detecting and treating incidental pharyngeal carriage of GAS in children with viral pharyngitis.

Prior upregulation of interferon pathways in the nasopharynx impacts viral shedding following live attenuated influenza vaccine challenge in children

In children lacking influenza-specific adaptive immunity, upper respiratory tract innate immune responses may influence viral replication and disease outcome. We use trivalent live attenuated influenza vaccine (LAIV) as a surrogate challenge model in children aged 24-59 months to identify pre-infection mucosal transcriptomic signatures associated with subsequent viral shedding. Upregulation of interferon signaling pathways prior to LAIV is significantly associated with lower strain-specific viral loads (VLs) at days 2 and 7. Several interferon-stimulated genes are differentially expressed in children with pre-LAIV asymptomatic respiratory viral infections and negatively correlated with LAIV VLs. Upregulation of genes enriched in macrophages, neutrophils, and eosinophils is associated with lower VLs and found more commonly in children with asymptomatic viral infections. Variability in pre-infection mucosal interferon gene expression in children may impact the course of subsequent influenza infections. This variability may be due to frequent respiratory viral infections, demonstrating the potential importance of mucosal virus-virus interactions in children.

A comparison of host response strategies to distinguish bacterial and viral infection

OBJECTIVES

Compare three host response strategies to distinguish bacterial and viral etiologies of acute respiratory illness (ARI).

METHODS

In this observational cohort study, procalcitonin, a 3-protein panel (CRP, IP-10, TRAIL), and a host gene expression mRNA panel were measured in 286 subjects with ARI from four emergency departments. Multinomial logistic regression and leave-one-out cross validation were used to evaluate the protein and mRNA tests.

RESULTS

The mRNA panel performed better than alternative strategies to identify bacterial infection: AUC 0.93 vs. 0.83 for the protein panel and 0.84 for procalcitonin (P<0.02 for each comparison). This corresponded to a sensitivity and specificity of 92% and 83% for the mRNA panel, 81% and 73% for the protein panel, and 68% and 87% for procalcitonin, respectively. A model utilizing all three strategies was the same as mRNA alone. For the diagnosis of viral infection, the AUC was 0.93 for mRNA and 0.84 for the protein panel (p<0.05). This corresponded to a sensitivity and specificity of 89% and 82% for the mRNA panel, and 85% and 62% for the protein panel, respectively.

CONCLUSIONS

A gene expression signature was the most accurate host response strategy for classifying subjects with bacterial, viral, or non-infectious ARI.

Novel Biomarkers Differentiating Viral from Bacterial Infection in Febrile Children: Future Perspectives for Management in Clinical Praxis

Differentiating viral from bacterial infections in febrile children is challenging and often leads to an unnecessary use of antibiotics. There is a great need for more accurate diagnostic tools. New molecular methods have improved the particular diagnostics of viral respiratory tract infections, but defining etiology can still be challenging, as certain viruses are frequently detected in asymptomatic children. For the detection of bacterial infections, time consuming cultures with limited sensitivity are still the gold standard. As a response to infection, the immune system elicits a cascade of events, which aims to eliminate the invading pathogen. Recent studies have focused on these host–pathogen interactions to identify pathogen-specific biomarkers (gene expression profiles), or “pathogen signatures”, as potential future diagnostic tools. Other studies have assessed combinations of traditional bacterial and viral biomarkers (C-reactive protein, interleukins, myxovirus resistance protein A, procalcitonin, tumor necrosis factor-related apoptosis-inducing ligand) to establish etiology. In this review we discuss the performance of such novel diagnostics and their potential role in clinical praxis. In conclusion, there are several promising novel biomarkers in the pipeline, but well-designed randomized controlled trials are needed to evaluate the safety of using these novel biomarkers to guide clinical decisions.

Discriminating Bacterial and Viral Infection Using a Rapid Host Gene Expression Test

OBJECTIVES

Host gene expression signatures discriminate bacterial and viral infection but have not been translated to a clinical test platform. This study enrolled an independent cohort of patients to describe and validate a first-in-class host response bacterial/viral test.

DESIGN

Subjects were recruited from 2006 to 2016. Enrollment blood samples were collected in an RNA preservative and banked for later testing. The reference standard was an expert panel clinical adjudication, which was blinded to gene expression and procalcitonin results.

SETTING

Four U.S. emergency departments.

PATIENTS

Six-hundred twenty-three subjects with acute respiratory illness or suspected sepsis.

INTERVENTIONS

Forty-five-transcript signature measured on the BioFire FilmArray System (BioFire Diagnostics, Salt Lake City, UT) in ~45 minutes.

MEASUREMENTS AND MAIN RESULTS

Host response bacterial/viral test performance characteristics were evaluated in 623 participants (mean age 46 yr; 45% male) with bacterial infection, viral infection, coinfection, or noninfectious illness. Performance of the host response bacterial/viral test was compared with procalcitonin. The test provided independent probabilities of bacterial and viral infection in ~45 minutes. In the 213-subject training cohort, the host response bacterial/viral test had an area under the curve for bacterial infection of 0.90 (95% CI, 0.84-0.94) and 0.92 (95% CI, 0.87-0.95) for viral infection. Independent validation in 209 subjects revealed similar performance with an area under the curve of 0.85 (95% CI, 0.78-0.90) for bacterial infection and 0.91 (95% CI, 0.85-0.94) for viral infection. The test had 80.1% (95% CI, 73.7-85.4%) average weighted accuracy for bacterial infection and 86.8% (95% CI, 81.8-90.8%) for viral infection in this validation cohort. This was significantly better than 68.7% (95% CI, 62.4-75.4%) observed for procalcitonin (p < 0.001). An additional cohort of 201 subjects with indeterminate phenotypes (coinfection or microbiology-negative infections) revealed similar performance.

CONCLUSIONS

The host response bacterial/viral measured using the BioFire System rapidly and accurately discriminated bacterial and viral infection better than procalcitonin, which can help support more appropriate antibiotic use.

Respiratory Viral and Bacterial Factors That Influence Early Childhood Asthma

Asthma is a chronic respiratory condition characterised by episodes of shortness of breath due to reduced airway flow. The disease is triggered by a hyperreactive immune response to innocuous allergens, leading to hyper inflammation, mucus production, changes in structural cells lining the airways, and airway hyperresponsiveness. Asthma, although present in adults, is considered as a childhood condition, with a total of about 6.2 million children aged 18 and below affected globally. There has been progress in understanding asthma heterogeneity in adults, which has led to better patient stratification and characterisation of multiple asthma endotypes with distinct, but overlapping inflammatory features. The asthma inflammatory profile in children is not well-defined and heterogeneity of the disease is less described. Although many factors such as genetics, food allergies, antibiotic usage, type of birth, and cigarette smoke exposure can influence asthma development particularly in children, respiratory infections are thought to be the major contributing factor in poor lung function and onset of the disease. In this review, we focus on viral and bacterial respiratory infections in the first 10 years of life that could influence development of asthma in children. We also review literature on inflammatory immune heterogeneity in asthmatic children and how this overlaps with early lung development, poor lung function and respiratory infections. Finally, we review animal studies that model early development of asthma and how these studies could inform future therapies and better understanding of this complex disease.

Immune profiles provide insights into respiratory syncytial virus disease severity in young children

Respiratory syncytial virus (RSV) is associated with major morbidity in infants, although most cases result in mild disease. The pathogenesis of the disease is incompletely understood, especially the determining factors of disease severity. A better characterization of these factors may help with development of RSV vaccines and antivirals. Hence, identification of a "safe and protective" immunoprofile induced by natural RSV infection could be used as a as a surrogate of ideal vaccine-elicited responses in future clinical trials. In this study, we integrated blood transcriptional and cell immune profiling, RSV loads, and clinical data to identify factors associated with a mild disease phenotype in a cohort of 190 children <2 years of age. Children with mild disease (outpatients) showed higher RSV loads, greater induction of interferon (IFN) and plasma cell genes, and decreased expression of inflammation and neutrophil genes versus children with severe disease (inpatients). Additionally, only infants with severe disease had increased numbers of HLA-DR^low monocytes, not present in outpatients. Multivariable analyses confirmed that IFN overexpression was associated with decreased odds of hospitalization, whereas increased numbers of HLA-DR^low monocytes were associated with increased risk of hospitalization. These findings suggest that robust innate immune responses are associated with mild RSV infection in infants.

Future Biomarkers for Infection and Inflammation in Febrile Children

Febrile patients, suffering from an infection, inflammatory disease or autoimmunity may present with similar or overlapping clinical symptoms, which makes early diagnosis difficult. Therefore, biomarkers are needed to help physicians form a correct diagnosis and initiate the right treatment to improve patient outcomes following first presentation or admittance to hospital. Here, we review the landscape of novel biomarkers and approaches of biomarker discovery. We first discuss the use of current plasma parameters and whole blood biomarkers, including results obtained by RNA profiling and mass spectrometry, to discriminate between bacterial and viral infections. Next we expand upon the use of biomarkers to distinguish between infectious and non-infectious disease. Finally, we discuss the strengths as well as the potential pitfalls of current developments. We conclude that the use of combination tests, using either protein markers or transcriptomic analysis, have advanced considerably and should be further explored to improve current diagnostics regarding febrile infections and inflammation. If proven effective when combined, these biomarker signatures will greatly accelerate early and tailored treatment decisions.

Association of nasopharyngeal viruses and pathogenic bacteria in children and their parents with and without HIV

BACKGROUND

Bacteria and respiratory viruses co-occur in the nasopharynx, and their interactions may impact pathogenesis of invasive disease. Associations of viruses and bacteria in the nasopharynx may be affected by HIV.

METHODS

We conducted a nested case-control study from a larger cohort study of banked nasopharyngeal swabs from families with and without HIV in West Bengal India, to look at the association of viruses and bacteria in the nasopharynx of parents and children when they are asymptomatic. Quantitative polymerase chain reaction for 4 bacteria and 21 respiratory viruses was run on 92 random nasopharyngeal swabs from children--49 from children living with HIV (CLH) and 43 from HIV uninfected children (HUC)-- and 77 swabs from their parents (44 parents of CLH and 33 parents of HUC).

RESULTS

Bacteria was found in 67% of children, viruses in 45%, and both in 27% of child samples. Staphylococcus aureus (53%) was the most common bacteria, followed by Streptococcus pneumoniae (pneumococcus) (37%) in children and parents (53, 20%). Regardless of HIV status, viruses were detected in higher numbers (44%) in children than their parents (30%) (p = 0.049), particularly rhinovirus (p = 0.02). Human rhinovirus was the most frequently found virus in both CLH and HUC. Children with adenovirus were at six times increased risk of also having pneumococcus (Odds ratio OR 6, 95% CI 1.12-31.9) regardless of HIV status. In addition, the presence of rhinovirus in children was associated with increased pneumococcal density (Regression coeff 4.5, 1.14-7.9). In CLH the presence of rhinovirus increased the risk of pneumococcal colonization by nearly sixteen times (OR 15.6, 1.66-146.4), and, pneumococcus and S. aureus dual colonization by nearly nine times (OR 8.7).

CONCLUSIONS

Children more frequently carried viruses regardless of HIV status. In CLH the presence of rhinovirus, the most frequently detected virus, significantly increased co-colonization with pneumococcus and S. aureus.

Multi-cohort analysis of host immune response identifies conserved protective and detrimental modules associated with severity across viruses

Viral infections induce a conserved host response distinct from bacterial infections. We hypothesized that the conserved response is associated with disease severity and is distinct between patients with different outcomes. To test this, we integrated 4,780 blood transcriptome profiles from patients aged 0 to 90 years infected with one of 16 viruses, including SARS-CoV-2, Ebola, chikungunya, and influenza, across 34 cohorts from 18 countries, and single-cell RNA sequencing profiles of 702,970 immune cells from 289 samples across three cohorts. Severe viral infection was associated with increased hematopoiesis, myelopoiesis, and myeloid-derived suppressor cells. We identified protective and detrimental gene modules that defined distinct trajectories associated with mild versus severe outcomes. The interferon response was decoupled from the protective host response in patients with severe outcomes. These findings were consistent, irrespective of age and virus, and provide insights to accelerate the development of diagnostics and host-directed therapies to improve global pandemic preparedness.

Presence of microorganisms in children with pharyngotonsillitis and healthy controls: a prospective study in primary healthcare

Purpose

Most studies on paediatric pharyngotonsillitis focus on group A streptococci. This study, however, analyses a broad spectrum of bacteria and viruses related to paediatric pharyngotonsillitis and evaluates their associated clinical symptoms and courses.

Methods

This observational prospective study in primary healthcare includes 77 children aged < 15 with a sore throat and 34 asymptomatic children, all of whom were sampled from the tonsils with an E-swab^® for analysis with culture and PCR for 14 bacteria and 15 viruses. Patients were evaluated clinically, and their symptoms recorded in diaries for 10 days. Participants were followed up for 3 months by reviewing medical records.

Results

A pathogen was detected in 86% of patients and in 71% of controls (P = 0.06). Bacteria were found in 69% of patients and 59% of controls (P = 0.3), and viruses in 36% and 26%, respectively (P = 0.3). Group A streptococci was the most common finding, with a prevalence of 49% and 32%, respectively (P = 0.1). Clinical signs were not useful for distinguishing pathogens. None of the controls and 16% of the patients reconsulted for a sore throat within 3 months.

Conclusion

Bacteria were more common than viruses in both study groups. The high rate of pathogens in asymptomatic children interferes with diagnoses based on aetiology.

Supplementary Information

The online version contains supplementary material available at 10.1007/s15010-021-01595-9.

A host-based two-gene model for the identification of bacterial infection in general clinical settings

OBJECTIVES

In this study, we aimed to develop a simple gene model to identify bacterial infection, which can be implemented in general clinical settings.

METHODS

We used a clinically availablereal-time quantitative polymerase chain reaction platform to conduct focused gene expression assays on clinical blood samples. Samples were collected from 2 tertiary hospitals.

RESULTS

We found that the 8 candidate genes for bacterial infection were significantly dysregulated in bacterial infection and displayed good performance in group classification, whereas the 2 genes for viral infection displayed poor performance. A two-gene model (S100A12 and CD177) displayed 93.0% sensitivity and 93.7% specificity in the modeling stage. In the independent validation stage, 87.8% sensitivity and 96.6% specificity were achieved in one set of case-control groups, and 93.6% sensitivity and 97.1% specificity in another set.

CONCLUSIONS

We have validated the signature genes for bacterial infection and developed a two-gene model to identify bacterial infection in general clinical settings.

Viral Loads and Disease Severity in Children with Rhinovirus-Associated Illnesses

The role of rhinoviruses (RVs) in children with clinical syndromes not classically associated with RV infections is not well understood. We analyzed a cohort of children ≤21 years old who were PCR+ for RV at a large Pediatric Hospital from 2011 to 2013. Using univariate and multivariable logistic regression, we analyzed the associations between demographic, clinical characteristics, microbiology data, and clinical outcomes in children with compatible symptoms and incidental RV detection. Of the 2473 children (inpatients and outpatients) with an RV+ PCR, 2382 (96%) had compatible symptoms, and 91 (4%) did not. The overall median age was 14 months and 78% had underlying comorbidities. No differences in RV viral loads were found according to the presence of compatible symptoms, while in children with classic RV symptoms, RV viral loads were higher in single RV infections versus RV viral co-infections. Bacterial co-infections were more common in RV incidental detection (7.6%) than in children with compatible symptoms (1.9%, p < 0.001). The presence of compatible symptoms independently increased the odds ratio (OR, 95% CI) of hospitalization 4.8 (3.1-7.4), prolonged hospital stays 1.9 (1.1-3.1), need for oxygen 12 (5.8-25.0) and pediatric intensive care unit (PICU) admission 4.13 (2.0-8.2). Thus, despite comparable RV loads, disease severity was significantly worse in children with compatible symptoms.

Validation of a host gene expression test for bacterial/viral discrimination in immunocompromised hosts

BACKGROUND

Host gene expression has emerged as a complementary strategy to pathogen detection tests for the discrimination of bacterial and viral infection. The impact of immunocompromise on host response tests remains unknown. We evaluated a host response test discriminating bacterial, viral, and non-infectious conditions in immunocompromised subjects.

METHODS

An 81-gene signature was measured using RT-PCR in subjects with immunocompromise (chemotherapy, solid organ transplant, immunomodulatory agents, AIDS) with bacterial infection, viral infection, or noninfectious illness. A regularized logistic regression model trained in immunocompetent subjects was used to estimate the likelihood of each class in immunocompromised subjects.

RESULTS

Accuracy in the 136-subject immunocompetent training cohort was 84.6% for bacterial vs. non-bacterial discrimination and 80.8% for viral vs. non-viral discrimination. Model validation in 134 immunocompromised subjects showed overall accuracy of 73.9% for bacterial infection (p=0.04 relative to immunocompetent subjects) and 75.4% for viral infection (p=0.30). A scheme reporting results by quartile improved test utility. The highest probability quartile ruled-in bacterial and viral infection with 91.4% and 84.0% specificity, respectively. The lowest probability quartile ruled-out infection with 90.1% and 96.4% sensitivity for bacterial and viral infection, respectively. Performance was independent of the type or number of immunocompromising conditions.

CONCLUSION

A host gene expression test discriminated bacterial, viral, and non-infectious etiologies at a lower overall accuracy in immunocompromised patients compared to immunocompetent patients, though this difference was only significant for bacterial infection classification. With modified interpretive criteria, a host response strategy may offer clinically useful diagnostic information for patients with immunocompromise.

Single-cell RNA-Seq revealed profound immune alteration in the peripheral blood of patients with bacterial infection

OBJECTIVES

Bacterial infection remains one of the greatest threats to human health. However, how human hosts respond to bacterial infection has not been thoroughly understood. Better understanding of this response will improve human health.

METHODS

Here, we conducted an investigation on host response to bacterial infection using unperturbed clinical samples and single-cell RNA-Seq (scRNA-Seq) technology. To evaluate immune alteration upon bacterial infection in scRNA-Seq data of peripheral blood mononuclear cells (PBMCs), we developed a barcode analytical framework named PBMCode.

RESULTS

Using this PBMCode framework, we revealed profound immune alteration in peripheral blood under bacterial infection, including the emergence of natural killer T (NKT) cell cluster, reduction of B cell population, and considerable changes in T cells and monocytes. In addition, we also observed a large quantity of low-density neutrophils.

CONCLUSIONS

Our investigation on single cells provided unprecedented details in the alteration of both cell population and cell state under bacterial infection. These findings may be relevant to clinical decisions. The complexity of host response to bacterial infection revealed by scRNA-Seq deserves further attention in future studies.

Rhinovirus and asthma: Challenges and opportunities

Human rhinoviruses (RVs) are the primary aetiological agent of the common cold. Generally, the associated infection is mild and self‐limiting, but may also be associated with bronchiolitis in infants, pneumonia in the immunocompromised and exacerbation in patients with pulmonary conditions such as asthma or chronic obstructive pulmonary disease. Viral infection accounts for as many as two thirds of asthma exacerbations in children and more than half in adults. Allergy and asthma are major risk factors for more frequent and severe RV‐related illnesses. The prevalence of RV‐induced wheezing will likely continue to increase given that asthma affects a significant proportion of the population, with allergic asthma accounting for the majority. Several new respiratory viruses and their subgroups have been discovered, with various degrees of relevance. This review will focus on RV infection in the context of the epidemiologic evidence, genetic variability, pathobiology, clinical studies in the context of asthma, differences with other viruses including COVID‐19 and current treatment interventions.

Role of probiotics to combat viral infections with emphasis on COVID-19

Interspecies transmissions of viruses between animals and humans may result in unpredictable pathogenic potential and new transmissible diseases. This mechanism has recently been exemplified by the discovery of new pathogenic viruses, such as the novel severe acute respiratory syndrome corona virus-2 (SARS-CoV-2) pandemic, Middle-East respiratory syndrome-coronavirus epidemic in Saudi Arabia, and the deadly outbreak of Ebola in West Africa. The. SARS-CoV-2 causes coronavirus disease-19 (COVID-19), which is having a massive global impact in terms of economic disruption, and, above all, human health. The disease is characterized by dry cough, fever, fatigue, myalgia, and dyspnea. Other symptoms include headache, sore throat, rhinorrhea, and gastrointestinal disorders. Pneumonia appears to be the most common and severe manifestation of the infection. Currently, there is no vaccine or specific drug for COVID-19. Further, the development of new antiviral requires a considerable length of time and effort for drug design and validation. Therefore, repurposing the use of natural compounds can provide alternatives and can support therapy against COVID-19. In this review, we comprehensively discuss the prophylactic and supportive therapeutic role of probiotics for the management of COVID-19. In addition, the unique role of probiotics to modulate the gut microbe and assert gut homeostasis and production of interferon as an antiviral mechanism is described. Further, the regulatory role of probiotics on gut-lung axis and mucosal immune system for the potential antiviral mechanisms is reviewed and discussed.Key points• Gut microbiota role in antiviral diseases• Factors influencing the antiviral mechanism• Probiotics and Covid-19.

The Feasibility of Host Transcriptome Profiling as a Diagnostic Tool for Microbial Etiology in Childhood Cancer Patients with Febrile Neutropenia

Infection is a common and serious complication of cancer treatment in children that often presents as febrile neutropenia (FN). Gene-expression profiling techniques can reveal transcriptional signatures that discriminate between viral, bacterial and asymptomatic infections in otherwise healthy children. Here, we examined whether gene-expression profiling was feasible in children with FN who were undergoing cancer treatment. The blood transcriptome of the children (n = 63) was investigated at time of FN diagnosed as viral, bacterial, co-infection or unknown etiology, respectively, and compared to control samples derived from 12 of the patients following the FN episode. RNA sequencing was successful in 43 (68%) of the FN episodes. Only two genes were significantly differentially expressed in the bacterial versus the control group. Significantly up-regulated genes in patients with the other three etiologies versus the control group were enriched with cellular processes related to proliferation and cellular stress response, with no clear enrichment with innate responses to pathogens. Among the significantly down-regulated genes, a few clustered into pathways connected to responses to infection. In the present study of children during cancer treatment, the blood transcriptome was not suitable for determining the etiology of FN because of too few circulating immune cells for reliable gene expression analysis.

Blood genome expression profiles in infants with congenital cytomegalovirus infection

Congenital CMV infection (cCMVi) affects 0.5–1% of all live births worldwide, making it the leading cause of sensorineural hearing loss (SNHL) in childhood. The majority of infants with cCMVi have normal hearing at birth, but are at risk of developing late-onset SNHL. Currently, we lack reliable biomarkers to predict the development of SNHL in these infants. Here, we evaluate blood transcriptional profiles in 80 infants with cCMVi (49 symptomatic, 31 asymptomatic), enrolled in the first 3 weeks of life, and followed for 3 years to assess emergence of late-onset SNHL. The biosignatures of symptomatic and asymptomatic cCMVi are indistinguishable, suggesting that immune responses of infants with asymptomatic and symptomatic cCMVi are not different. Random forest analyses of initial samples in infants with cCMVi, irrespective of their clinical classification, identify a 16-gene classifier signature associated with the development of SNHL with 92% accuracy, suggesting its potential value as a biomarker.

Congenital CMV infection can result in sensorineural hearing loss, but predicting this outcome is not yet possible. Here, the authors show that while blood gene expression profiles are not substantially different between symptomatic and asymptomatic infants with congenital CMV infection, a 16-gene signature is identified and able to predict late-onset hearing loss in these children.

Detection of Respiratory Syncytial Virus or Rhinovirus Weeks After Hospitalization for Bronchiolitis and the Risk of Recurrent Wheezing

BACKGROUND

In severe bronchiolitis, it is unclear if delayed clearance or sequential infection of respiratory syncytial virus (RSV) or rhinovirus (RV) is associated with recurrent wheezing.

METHODS

In a 17-center severe bronchiolitis cohort, we tested nasopharyngeal aspirates (NPA) upon hospitalization and 3 weeks later (clearance swab) for respiratory viruses using PCR. The same RSV subtype or RV genotype in NPA and clearance swab defined delayed clearance (DC); a new RSV subtype or RV genotype at clearance defined sequential infection (SI). Recurrent wheezing by age 3 years was defined per national asthma guidelines.

RESULTS

Among 673 infants, RSV DC and RV DC were not associated with recurrent wheezing, and RSV SI was rare. The 128 infants with RV SI (19%) had nonsignificantly higher risk of recurrent wheezing (hazard ratio [HR], 1.31; 95% confidence interval [CI], .95-1.80; P = .10) versus infants without RV SI. Among infants with RV at hospitalization, those with RV SI had a higher risk of recurrent wheezing compared to children without RV SI (HR, 2.49; 95% CI, 1.22-5.06; P = .01).

CONCLUSIONS

Among infants with severe bronchiolitis, those with RV at hospitalization followed by a new RV infection had the highest risk of recurrent wheezing.

Host response-based screening to identify undiagnosed cases of COVID-19 and expand testing capacity

The COVID-19 pandemic has created unprecedented challenges in diagnostic testing. At the beginning of the epidemic, a confluence of factors resulted in delayed deployment of PCR-based diagnostic tests, resulting in lack of testing of individuals with symptoms of the disease. Although these tests are now more widely available, it is estimated that a three- to ten-fold increase in testing capacity will be required to ensure adequate surveillance as communities reopen(1). In response to these challenges, we evaluated potential roles of host-response based screening in the diagnosis of COVID-19. Previous work from our group showed that the nasopharyngeal (NP) level of CXCL10, a protein produced as part of the host response to viral infection, is a sensitive predictor of respiratory virus infection across a wide spectrum of viruses(2). Here, we show that NP CXCL10 is elevated during SARS-CoV-2 infection and use a CXCL10-based screening strategy to identify four undiagnosed cases of COVID-19 in Connecticut in early March. In a second set of samples tested at the Yale New Haven Hospital, we show that NP CXCL10 had excellent performance as a rule-out test (NPV 0.99, 95% C.I. 0.985-0.997). Our results demonstrate how biomarker-based screening could be used to leverage existing PCR testing capacity to rapidly enable widespread testing for COVID-19.

Baseline and Disease-Induced Transcriptional Profiles in Children with Sickle Cell Disease

Acute chest syndrome (ACS) is a significant cause of morbidity and mortality in sickle cell disease (SCD), but preventive, diagnostic, and therapeutic options are limited. Further, ACS and acute vasoccclusive pain crises (VOC) have overlapping features, which causes diagnostic dilemmas. We explored changes in gene expression profiles among patients with SCD hospitalized for VOC and ACS episodes to better understand ACS disease pathogenesis. Whole blood RNA-Seq was performed for 20 samples from children with SCD at baseline and during a hospitalization for either an ACS (n = 10) or a VOC episode (n = 10). Respiratory viruses were identified from nasopharyngeal swabs. Functional gene analyses were performed using modular repertoires, IPA, Gene Ontology, and NetworkAnalyst 3.0. The VOC group had a numerically higher percentage of female, older, and hemoglobin SS participants compared to the ACS group. Viruses were detected in 50% of ACS cases and 20% of VOC cases. We identified 3004 transcripts that were differentially expressed during ACS episodes, and 1802 transcripts during VOC episodes. Top canonical pathways during ACS episodes were related to interferon signaling, neuro-inflammation, pattern recognition receptors, and macrophages. Top canonical pathways in patients with VOC included IL-10 signaling, iNOS signaling, IL-6 signaling, and B cell signaling. Several genes related to antimicrobial function were down-regulated during ACS compared to VOC. Gene enrichment nodal interactions demonstrated significantly altered pathways during ACS and VOC. A complex network of changes in innate and adaptive immune gene expression were identified during both ACS and VOC episodes. These results provide unique insights into changes during acute events in children with SCD.

Current Trends in Diagnostics of Viral Infections of Unknown Etiology

Viruses are evolving at an alarming rate, spreading and inconspicuously adapting to cutting-edge therapies. Therefore, the search for rapid, informative and reliable diagnostic methods is becoming urgent as ever. Conventional clinical tests (PCR, serology, etc.) are being continually optimized, yet provide very limited data. Could high throughput sequencing (HTS) become the future gold standard in molecular diagnostics of viral infections? Compared to conventional clinical tests, HTS is universal and more precise at profiling pathogens. Nevertheless, it has not yet been widely accepted as a diagnostic tool, owing primarily to its high cost and the complexity of sample preparation and data analysis. Those obstacles must be tackled to integrate HTS into daily clinical practice. For this, three objectives are to be achieved: (1) designing and assessing universal protocols for library preparation, (2) assembling purpose-specific pipelines, and (3) building computational infrastructure to suit the needs and financial abilities of modern healthcare centers. Data harvested with HTS could not only augment diagnostics and help to choose the correct therapy, but also facilitate research in epidemiology, genetics and virology. This information, in turn, could significantly aid clinicians in battling viral infections.

Host Gene Expression in Nose and Blood for the Diagnosis of Viral Respiratory Infection

BACKGROUND

Recently there has been a growing interest in the potential for host transcriptomic analysis to augment the diagnosis of infectious diseases.

METHODS

We compared nasal and blood samples for evaluation of the host transcriptomic response in children with acute respiratory syncytial virus (RSV) infection, symptomatic non-RSV respiratory virus infection, asymptomatic rhinovirus infection, and virus-negative asymptomatic controls. We used nested leave-one-pair-out cross-validation and supervised principal components analysis to define small sets of genes whose expression patterns accurately classified subjects. We validated gene classification scores using an external data set.

RESULTS

Despite lower quality of nasal RNA, the number of genes detected by microarray in each sample type was equivalent. Nasal gene expression signal derived mainly from epithelial cells but also included a variable leukocyte contribution. The number of genes with increased expression in virus-infected children was comparable in nasal and blood samples, while nasal samples also had decreased expression of many genes associated with ciliary function and assembly. Nasal gene expression signatures were as good or better for discriminating between symptomatic, asymptomatic, and uninfected children.

CONCLSUSIONS

Our results support the use of nasal samples to augment pathogen-based tests to diagnose viral respiratory infection.

Antiviral Response in the Nasopharynx Identifies Patients With Respiratory Virus Infection

Background

Despite the high burden of respiratory infection and the importance of early and accurate diagnosis, there is no simple diagnostic test to rule in viral infection as a cause of respiratory symptoms.

Methods

We performed RNA sequencing on human nasal epithelial cells following stimulation of the intracellular viral recognition receptor RIG-I. Next, we evaluated whether measuring identified host mRNAs and proteins from patient nasopharyngeal swabs could predict the presence of a respiratory virus in the sample.

Results

Our first study showed that a signature of 3 mRNAs, CXCL10, IFIT2, and OASL, predicted respiratory virus detection with an accuracy of 97% (95% confidence interval [CI], 0.9–1.0), and identified proteins correlating with virus detection. In a second study, elevated CXCL11 or CXCL10 protein levels identified samples containing respiratory viruses, including viruses not on the initial test panel. Overall area under the curve (AUC) values were: CXCL11 AUC = 0.901 (95% CI, 0.86–0.94); CXCL10 AUC = 0.85 (95% CI, 0.80–0.91).

Conclusions

Host antiviral mRNAs and single host proteins detectable using nasopharyngeal swabs accurately predict the presence of viral infection. This approach holds promise for developing rapid, cost-effective tests to improve management of patients with respiratory illnesses.

Viral Bacterial Interactions in Children: Impact on Clinical Outcomes

Respiratory viral infections are associated with significant morbidity and mortality in children < 5 years of age worldwide. Among all respiratory viruses, respiratory syncytial virus (RSV) is the world's leading cause of bronchiolitis and pneumonia in young children. There are known populations at risk for severe disease but the majority of children who require hospitalization for RSV infection are previously healthy. Viral and host factors have been associated with the pathogenesis of RSV disease; however, the mechanisms that explain the wide variability in the clinical presentation are not completely understood. Recent studies suggest that the complex interaction between the respiratory microbiome, the host's immune response and the virus may have an impact on the pathogenesis and severity of RSV infection. In this review, we summarize the current evidence regarding the epidemiologic link, the mechanisms of viral-bacterial interactions, and the associations between the upper respiratory tract microbiome and RSV disease severity.

Relationship between nasopharyngeal microbiota and patient's susceptibility to viral infection

Introduction: The burden of respiratory viral infections is a global public health concern with significant mortality, morbidity, and economic impact. While Koch's postulate led to considering only the etiological agent, numerous works have demonstrated that commensal microbes could contribute to both the susceptibility and the severity of these infections, in particular those of the nasopharynx. Areas covered: Herein, we first propose to briefly recall the historical background that led to considering microbes inhabiting the nasopharyngeal microbiota as a potential contributor to human viral infections. We describe the evolution of the normal nasopharyngeal microbiota composition over time, especially during the first year of life. We aimed to resume the changes of the nasopharyngeal microbiota during viral respiratory infections. We also develop how nasopharyngeal microbiota could contribute to the acquisition of respiratory viral infections. We finally provide the potential therapeutic perspectives deriving from these findings. Expert opinion: Prospective studies focusing on children have identified that nasopharyngeal microbiota composition is associated with predisposition to acute respiratory illness and bronchiolitis, while data are scarce regarding adults. For the latter, further works are needed, in particular as a part of the multi-OMICS approach that should probably be performed in conjunction with gut microbiota studies.

Infant Immune Response to Respiratory Viral Infections

Of all respiratory viruses that affect infants, respiratory syncytial virus (RSV) and rhinovirus (RV) represent the leading pathogens causing acute disease (bronchiolitis) and are associated with the development of recurrent wheezing and asthma. The immune system in infants is still developing, and several factors contribute to their increased susceptibility to viral infections. These factors include differences in pathogen detection, weaker interferon responses, lack of immunologic memory toward the invading pathogen, and T-cell responses that are balanced to promote tolerance and restrain inflammation. These aspects are reviewed here with a focus on RSV and RV infections.

Introduction to Techniques and Methodologies for Characterizing the Human Respiratory Virome

There have been great advances in the methodologies available for the detection of respiratory viruses. Accompanying this, our knowledge surrounding the impact of these viruses has also made a great leap forward. We have come a long way from the once commonly accepted belief that the lower respiratory tract was sterile and that the detection of any microbial species must represent a breach in host defence and likely be associated with symptomatic infection. With the advent of molecular detection techniques and improvements in sequencing-based methodologies to make these tools more accessible and cost effective, we now know that there is an abundant and diverse ecosystem within the lower-respiratory tract. This chapter will outline the clinical impact of the human respiratory virome, techniques for sampling the lower respiratory tract, the evolution of the diagnostic tools available, and the current limitations in our instruments and knowledge in this area. The human respiratory virome is an exciting new area of research that will continue to grow with the aid of the methodologies outlined in the following chapters and the advent of even more efficient tools in the future.

Secondhand smoke alters arachidonic acid metabolism and inflammation in infants and children with cystic fibrosis

BACKGROUND

Mechanisms that facilitate early infection and inflammation in cystic fibrosis (CF) are unclear. We previously demonstrated that children with CF and parental-reported secondhand smoke exposure (SHSe) have increased susceptibility to bacterial infections. SHSe hinders arachidonic acid (AA) metabolites that mediate immune function in patients without CF, and may influence CF immune dysfunction. We aimed to define SHSe's impact on inflammation mediators and infection in children with CF.

METHODS

Seventy-seven children with CF <10 years of age (35 infants <1 year; 42 children 1-10 years) were enrolled and hair nicotine concentrations measured as an objective surrogate of SHSe. AA signalling by serum and macrophage lipidomics, inflammation using blood transcriptional profiles and in vitro macrophage responses to bacterial infection after SHSe were assessed.

RESULTS

Hair nicotine concentrations were elevated in 63% of patients. Of the AA metabolites measured by plasma lipidomics, prostaglandin D₂ (PGD₂) concentrations were decreased in children with CF exposed to SHSe, and associated with more frequent hospitalisations (p=0.007) and worsened weight z scores (p=0.008). Children with CF exposed to SHSe demonstrated decreased expression of the prostaglandin genes PTGES3 and PTGR2 and overexpression of inflammatory pathways. These findings were confirmed using an in vitro model, where SHSe was associated with a dose-dependent decrease in PGD₂ and increased methicillin-resistant Staphylococcus aureus survival in human CF macrophages.

CONCLUSIONS

Infants and young children with CF and SHSe have altered AA metabolism and dysregulated inflammatory gene expression resulting in impaired bacterial clearance. Our findings identified potential therapeutic targets to halt early disease progression associated with SHSe in the young population with CF.

Detection of cytomegalovirus in saliva from infants undergoing sepsis evaluation in the neonatal intensive care unit: the VIRIoN-C study

Objective To determine the frequency of detection of cytomegalovirus (CMV) among infants evaluated for late-onset sepsis in the neonatal intensive care unit (NICU). Methods This study was a prospective cohort study. Results During the 13-month study, 84 infants underwent 116 sepsis evaluations, and CMV DNA was detected in saliva in three (4%) infants (median: gestational age 28 weeks, birth weight 950 g), representing 5% (n=6) of all sepsis evaluations. One infant had CMV DNA detected in saliva in all four sepsis evaluations. Two infants had acquired CMV infection, while the timing of CMV acquisition could not be determined in one infant. Two of the three infants had concomitant Gram-negative bacteremia and urinary tract infections (UTIs), two developed severe bronchopulmonary dysplasia (BPD) and none died. Conclusion Detection of CMV DNA in saliva occurred in 4% of infants and 5% of sepsis evaluations. Persistence of CMV DNA shedding in saliva made attribution of clinical illness difficult to ascertain.

Integrating host response and unbiased microbe detection for lower respiratory tract infection diagnosis in critically ill adults

Lower respiratory tract infections (LRTIs) are the leading cause of infectious disease-related deaths worldwide yet remain challenging to diagnose because of limitations in existing microbiologic tests. In critically ill patients, noninfectious respiratory syndromes that resemble LRTIs further complicate diagnosis and confound targeted treatment. To address this, we developed a metagenomic sequencing-based approach that simultaneously interrogates three core elements of acute airway infections: the pathogen, airway microbiome, and host response. We studied this approach in a prospective cohort of critically ill patients with acute respiratory failure and found that combining pathogen, microbiome, and host gene expression metrics achieved accurate LRTI diagnosis and identified etiologic pathogens in patients with clinically identified infections but otherwise negative testing.

Lower respiratory tract infections (LRTIs) lead to more deaths each year than any other infectious disease category. Despite this, etiologic LRTI pathogens are infrequently identified due to limitations of existing microbiologic tests. In critically ill patients, noninfectious inflammatory syndromes resembling LRTIs further complicate diagnosis. To address the need for improved LRTI diagnostics, we performed metagenomic next-generation sequencing (mNGS) on tracheal aspirates from 92 adults with acute respiratory failure and simultaneously assessed pathogens, the airway microbiome, and the host transcriptome. To differentiate pathogens from respiratory commensals, we developed a rules-based model (RBM) and logistic regression model (LRM) in a derivation cohort of 20 patients with LRTIs or noninfectious acute respiratory illnesses. When tested in an independent validation cohort of 24 patients, both models achieved accuracies of 95.5%. We next developed pathogen, microbiome diversity, and host gene expression metrics to identify LRTI-positive patients and differentiate them from critically ill controls with noninfectious acute respiratory illnesses. When tested in the validation cohort, the pathogen metric performed with an area under the receiver-operating curve (AUC) of 0.96 (95% CI, 0.86–1.00), the diversity metric with an AUC of 0.80 (95% CI, 0.63–0.98), and the host transcriptional classifier with an AUC of 0.88 (95% CI, 0.75–1.00). Combining these achieved a negative predictive value of 100%. This study suggests that a single streamlined protocol offering an integrated genomic portrait of pathogen, microbiome, and host transcriptome may hold promise as a tool for LRTI diagnosis.

In situ Immune Signatures and Microbial Load at the Nasopharyngeal Interface in Children With Acute Respiratory Infection

Acute respiratory infection (ARI) is the most frequent cause for hospitalization in infants and young children. Using multiplexed nCounter technology to digitally quantify 600 human mRNAs in parallel with 14 virus- and 5 bacterium-specific RNAs, we characterized viral and bacterial presence in nasopharyngeal aspirates (NPA) of 58 children with ARI and determined the corresponding in situ immune profiles. NPA contained different groups of organisms and these were classified into bacterial (n = 27), viral (n = 5), codetection [containing both viral and bacterial transcripts (n = 21), or indeterminate intermediate where microbial load is below threshold (n = 5)]. We then identified differentially expressed immune transcripts (DEITs) comparing NPAs from symptomatic children vs. healthy controls, and comparing children presenting NPAs with detectable microbial load vs. indeterminate. We observed a strong innate immune response in NPAs, due to the presence of evolutionarily conserved type I Interferon (IFN)-stimulated genes (ISG), which was correlated with total bacterial and/or viral load. In comparison with indeterminate NPAs, adaptive immunity transcripts discriminated among viral, bacterial, and codetected microbial profiles. In viral NPAs, B cell transcripts were significantly enriched among DEITs, while only type III IFN was correlated with viral load. In bacterial NPAs, myeloid cells and coinhibitory transcripts were enriched and significantly correlated with bacterial load. In conclusion, digital nCounter transcriptomics provide a microbial and immunological in situ “snapshot” of the nasopharyngeal interface in children with ARI. This enabled discrimination among viral, bacterial, codetection, and indeterminate transcripts in the samples using non-invasive sampling.

Elucidating the Interaction of CF Airway Epithelial Cells and Rhinovirus: Using the Host-Pathogen Relationship to Identify Future Therapeutic Strategies

Chronic lung disease remains the primary cause of mortality in cystic fibrosis (CF). Growing evidence suggests respiratory viral infections are often more severe in CF compared to healthy peers and contributes to pulmonary exacerbations (PEx) and deterioration of lung function. Rhinovirus is the most prevalent respiratory virus detected, particularly during exacerbations in children with CF <5 years old. However, even though rhinoviral infections are likely to be one of the factors initiating the onset of CF lung disease, there is no effective targeted treatment. A better understanding of the innate immune responses by CF airway epithelial cells, the primary site of infection for viruses, is needed to identify why viral infections are more severe in CF. The aim of this review is to present the clinical impact of virus infection in both young children and adults with CF, focusing on rhinovirus infection. Previous in vitro and in vivo investigations looking at the mechanisms behind virus infection will also be summarized. The review will finish on the potential of transcriptomics to elucidate the host-pathogen responses by CF airway cells to viral infection and identify novel therapeutic targets.

Molecular Distance to Health Transcriptional Score and Disease Severity in Children Hospitalized With Community-Acquired Pneumonia

Background: Community-acquired pneumonia (CAP) is a leading cause of hospitalization and mortality in children. Diagnosis remains challenging and there are no reliable tools to objectively risk stratify patients or predict clinical outcomes. Molecular distance to health (MDTH) is a genomic score that measures the global perturbation of the transcriptional profile and may help classify patients by disease severity. We evaluated the value of MDTH to assess disease severity in children hospitalized with CAP.

Methods: Children hospitalized with CAP and matched healthy controls were enrolled in a prospective observational study. Blood samples were obtained for transcriptome analyses within 24 h of hospitalization. MDTH scores were calculated to assess disease severity and correlated with laboratory markers, such as white blood cell count, c-reactive protein (CRP), and procalcitonin (PCT), and clinical outcomes, including duration of fever and duration of hospitalization (LOS). Univariate and multivariable logistic regression were applied to assess factors associated with LOS and duration of fever after hospitalization.

Results: Among children hospitalized with CAP (n = 152), pyogenic bacteria (PB) were detected in 16 (11%), Mycoplasma pneumoniae was detected in 41 (28%), respiratory viruses (RV) alone were detected in 78 (51%), and no pathogen was detected in 17 (11%) children. Statistical group comparisons identified 6,726 genes differentially expressed in patients with CAP vs. healthy controls (n = 39). Children with confirmed PB had higher MDTH scores than those with RV (p < 0.05) or M. pneumoniae (p < 0.01) detected alone. CRP (r = 0.39, p < 0.0001), PCT (r = 0.39, p < 0.0001), and MDTHs (r = 0.24, p < 0.01) correlated with duration of fever, while only MDTHs correlated with LOS (r = 0.33, p < 0.0001). Unadjusted analyses showed that both higher CRP and MDTHs were associated with longer LOS (OR 1.04 [1–1.07] and 1.12 [1.04–1.20], respectively), however, only MDTH remained significant when adjusting for other covariates (aOR 1.11 [1.01–1.22]).

Conclusions: In children hospitalized with CAP MDTH score measured within 24 h of admission was independently associated with longer duration of hospitalization, regardless of the pathogen detected. This suggests that transcriptional biomarkers may represent a promising approach to assess disease severity in children with CAP.