High incidence of pulmonary bacterial co-infection in children with severe respiratory syncytial virus (RSV) bronchiolitis

Prevalence of Bacterial Codetection and Outcomes for Infants Intubated for Respiratory Infections

OBJECTIVES

To determine the prevalence of respiratory bacterial codetection in children younger than 2 years intubated for acute lower respiratory tract infection (LRTI), primarily viral bronchiolitis, and identify the association of codetection with mechanical ventilation duration.

DESIGN

Prospective observational study evaluating the prevalence of bacterial codetection (moderate/heavy growth of pathogenic bacterial plus moderate/many polymorphonuclear neutrophils) and the impact of codetection on invasive mechanical ventilation (IMV) duration.

SETTING

PICUs in 12 high and low/middle-income countries.

PATIENTS

Children younger than 2 years old requiring intubation and ICU admission for LRTI and who had a lower respiratory tract culture obtained at the time of intubation between December 1, 2019, and November 30, 2020.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Of the 472 analyzed patients (median age 4.5 mo), 55% had a positive respiratory culture and 29% ( n = 138) had codetection. 90% received early antibiotics starting at a median of 0.36 hours after respiratory culture. Median (interquartile range) IMV duration was 151 hours (88, 226), and there were 28 deaths (5.3%). Codetection was more common with younger age, a positive respiratory syncytial virus test, and an admission diagnosis of bronchiolitis; it was less common with an admission diagnosis of pneumonia, with admission to a low-/middle-income site, and in those receiving vasopressors. When adjusted for confounders, codetection was not associated with longer IMV duration (adjusted relative risk 0.854 [95% CI 0.684-1.065]). We could not exclude the possibility that codetection might be associated with a 30-hour shorter IMV duration compared with no codetection, although the CI includes the null value.

CONCLUSIONS

Bacterial codetection was present in almost a third of children younger than 2 years requiring intubation and ICU admission for LRTI, but this was not associated with prolonged IMV. Further large studies are needed to evaluate if codetection is associated with shorter IMV duration.

Risk Factors and Clinical Prognosis Associated With RSV-ALRI Intensive Care Unit Admission in Children <2 Years of Age: A Multicenter Study

BACKGROUND

Respiratory syncytial virus (RSV) is the leading cause of acute lower respiratory infections (ALRIs) in children <2 years of age. Currently, there are limited data on risk factors for very severe RSV-ALRI requiring intensive care unit (ICU) admission.

METHODS

We conducted a case-control study of children <2 years old admitted with RSV-ALRI to the Sydney Children's Hospital Network, comprising 2 large tertiary pediatric hospitals. Cases were children with laboratory-confirmed RSV-ALRI admitted to ICU, and controls were (1:2, matched on date of admission) children hospitalized with RSV-ALRI but not requiring ICU transfer. Data on risk factors were retrieved from the electronic medical record system. Adjusted odds ratios (aORs) with 95% confidence intervals (95% CI) associated with risk factors for ICU admission and the association with clinical and treatment factors were determined from logistic regression models.

RESULTS

A total of 44 (44%) of 100 cases and 90 (48.1%) of 187 controls were male. Age <6 months and preterm births were associated with a 2.10-fold (95% CI: 1.14-3.79) and 2.35-fold (95% CI: 1.26-4.41) increased risk in ICU admissions, respectively. The presence of any chronic health condition was a significant risk factor for ICU admission. The clinical presentations on admission more commonly seen in cases were apnea (aOR: 5.01, 95% CI: 1.50-17.13) and respiratory distress (aOR: 15.91, 95% CI: 4.52-55.97). Cases were more likely to be hospitalized for longer duration and require respiratory support.

CONCLUSIONS

Our results can be translated into a clinical risk algorithm to identify children at risk of very severe RSV disease.

Respiratory syncytial virus in pediatric patients admitted to a tertiary center in Amman: clinical characteristics, and age-related patterns

BACKGROUND

Respiratory syncytial virus (RSV) is a common cause of acute lower respiratory tract infections, particularly in infants and young children during winter. We aimed to study the demographics and clinical characteristics of RSV infections and age-related patterns.

METHODS

This retrospective study evaluated pediatric respiratory syncytial virus (RSV) infections conducted in Jordan from September 2021 to March 2022. Patients under the age of five who had viral polymerase chain reaction results showing RSV infection from nasopharyngeal aspiration were included. In addition, demographic information, medical history, and clinical data were gathered. These included comorbidities, outcomes, length of stay, ICU hospitalization, use of antibiotics, and oxygen supplementation.

RESULTS

A total of 199 patients were included. Most patients were males (56.8%) and less than one year (43.7%). Children aged between 1 and 2 years presented with more shortness of breath (90.1%) than infants and children more than two years (66.7% and 87%, respectively) (p < 0.001). Older children (> 2 years) were significantly more likely to use antibiotics and have ICU admission than younger children ≤ 2 years (p = 0.045 and 0.018, respectively). There was no relationship between age groups, recurrent hospitalization, previous RSV infection, oxygen therapy, coinfection, and hospitalization duration. The respiratory rate was higher among patients with co-infection (p = 0.031).

CONCLUSION

The current study provides information on the demographics and clinical characteristics of RSV infections. These findings contribute to a nuanced understanding of RSV infections in the specified population, emphasizing age-specific variations and clinical implications for better management strategies.

Frequency, Markers and Costs of Secondary Bacterial Infection in Pediatric Dengue

BACKGROUND

Secondary bacterial infection (SBI) occurs in a proportion of individuals with dengue and results in longer hospitalization, higher mortality, and increased health-related costs. However, the frequency, risk factors and predictive biomarkers of this comorbidity in pediatric dengue is partially known.

METHODS

We conducted a retrospective multicenter study in a dengue hyperendemic region of Colombia, analyzing 1597 children from two pediatric cohorts. We included children with confirmed dengue (mild to severe disease) and evaluated the rate of SBI, their clinical characteristics, diagnostic predictors and attention costs. We also assessed the diagnostic performance of plasma interleukin (IL)-6 for detecting SBI in pediatric dengue.

RESULTS

The frequency of SBI in children with dengue with warning signs in cohorts 1 and 2 was 2.4% and 7.3%, respectively, and this rate reached 30.7% and 38.2% in children with severe disease. Staphylococcus aureus and Escherichia coli were the more frequent infectious agents. Increased total leukocytes and C-reactive protein levels, as well as high IL-6 at hospital admission, in children <48 months of age were early indications of SBI in dengue. Higher rates of organ dysfunction, the requirement of a longer hospitalization and a 2.3-fold increase in attention costs were observed in SBI.

CONCLUSIONS

An important proportion of children with dengue course with SBI and exhibit higher morbidity. Elevated leukocytes, C-reactive protein and IL-6 in young children are early markers of SBI. Physicians should identify children with dengue and risk factors for SBI, microbiologically confirm the bacterial infection, and rationally and timely provide antimicrobial therapy.

Impact of Respiratory Bacterial Codetection on Outcomes in Ventilated Infants With Bronchiolitis

BACKGROUND

Viral bronchiolitis is a common cause of acute respiratory failure requiring intubation for infants. Bacterial respiratory tract infections can occur with bronchiolitis, although their prevalence and impact on outcomes are unclear, especially with increased use of noninvasive respiratory support.

METHODS

This was a single-center retrospective cohort study of children <2 years old requiring intubation in the emergency department for bronchiolitis from 2012 to 2017 who had viral testing plus a lower respiratory culture obtained. We evaluated the impact of bacterial codetection (positive respiratory culture plus moderate or many polymorphonuclear neutrophils on Gram stain) on mechanical ventilation (MV) duration and intensive care unit length of stay using multivariable gamma regression.

RESULTS

Of 149 patients enrolled, 52% had bacterial codetection. In adjusted analysis, patients with codetection had shorter MV duration [adjusted relative risk (aRR) 0.819, 95% confidence interval (CI): 0.69-0.98; marginal mean duration of 5.31 days (4.71-5.99) compared to 6.48 days (5.72-7.35) without codetection]. Patients with codetection had a shorter intensive care unit stay [aRR 0.806 (0.69-0.94); marginal mean length of stay 6.9 days (6.21-7.68) vs. 8.57 days (7.68-9.56) without codetection]. The association between codetection and duration of ventilation appears confined to those receiving earlier antibiotics (less than the median time) rather than later antibiotics [aRR 0.738 (0.56-0.95) for earlier vs. aRR 0.92 (0.70-1.18) for later].

CONCLUSIONS

Respiratory bacterial codetection is common and associated with shorter MV duration in infants requiring early intubation for bronchiolitis. Early antibiotics may contribute to these outcomes, but further multicenter studies are needed to understand the role of codetection and antibiotics on bronchiolitis outcomes.

Respiratory Syncytial Virus-Associated Deaths among Children under Five before and during the COVID-19 Pandemic in Bangladesh

Respiratory syncytial virus (RSV) is a leading cause of acute lower respiratory infections in young children worldwide. RSV-associated deaths in children are underreported in Bangladesh. We analyzed hospital-based surveillance data on severe acute respiratory infections (SARIs) in under-five children before (August 2009-February 2020) and during the COVID-19 pandemic (March 2020-March 2022). Using the World Health Organization definition, we identified SARI cases in 14 tertiary-level hospitals. Nasopharyngeal and oropharyngeal swabs were collected for real-time reverse-transcriptase-polymerase chain reaction (rRT-PCR) testing of six respiratory viruses, including RSV. SARI deaths during the pandemic (2.6%, 66) were higher than pre-pandemic (1.8%, 159; p < 0.001). Nearly half of pandemic deaths (47%) had underlying respiratory viruses, similar to the pre-pandemic rate (45%). RSV detection in deaths was consistent pre-pandemic (13%, 20/159) and during the pandemic (12%, 8/66). Children aged < 6 months constituted 57% (16) of RSV-related deaths. Evaluating interventions like maternal vaccination and infant monoclonal antibody prophylaxis is crucial to address RSV, a major contributor to under-five SARI deaths.

The impact of non-pharmacologic interventions on respiratory syncytial virus hospitalization during the COVID-19 pandemic: A retrospective study from Saudi Arabia

BACKGROUND

Acute respiratory tract infections (ARTIs) are frequently observed in infants and young children. The dynamics and transmission of ARTIs have been significantly impacted by the global COVID-19 pandemic. This study investigates the change in admission rates of Respiratory Syncytial virus (RSV) in a hospital in Saudi Arabia.

METHODS

The study included hospitalized pediatric patients who underwent RSV testing in three periods: pre-pandemic (2019), during the pandemic (2020-2021), and the immediate post-pandemic (2022). RSV testing was conducted using either PCR or antigen tests.

RESULTS

Between January 2019 to December 2022, out of 927 tested patients, 173 (18.7%) were positive for RSV. The yearly positivity rates were as follows: 42 (35.6%) of 118, 24 (33.3%) of 72, 15 (18.5%) of 81, and 92 (14%) of 656, yearly from 2019 to 2022, respectively (P < 0.00001). Among all cases, 150 (16.2%) required hospitalization, including 94 (62.7%) males and 56 (37.3%) females. The admission rate to the intensive care unit (ICU) was 25 (16.7%), and mechanical ventilation was required for 10 (6.6%) patients. The overall case fatality rate was 0.7%. A Binary logistic regression analysis showed upper respiratory tract symptoms were more common in patients admitted in 2019 compared to 2022 (odd ratio:20.9, 95% CI: 4.2-104.1, P value < 0.0001).

CONCLUSION

The study showed that there were differences in RSV infection before and after COVID-19. Understanding how COVID-19 mitigation measures affect RSV transmission can aid in the development of effective prevention and control strategies.

A cooperativity between virus and bacteria during respiratory infections

Respiratory tract infections remain the leading cause of morbidity and mortality worldwide. The burden is further increased by polymicrobial infection or viral and bacterial co-infection, often exacerbating the existing condition. Way back in 1918, high morbidity due to secondary pneumonia caused by bacterial infection was known, and a similar phenomenon was observed during the recent COVID-19 pandemic in which secondary bacterial infection worsens the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) condition. It has been observed that viruses paved the way for subsequent bacterial infection; similarly, bacteria have also been found to aid in viral infection. Viruses elevate bacterial infection by impairing the host's immune response, disrupting epithelial barrier integrity, expression of surface receptors and adhesion proteins, direct binding of virus to bacteria, altering nutritional immunity, and effecting the bacterial biofilm. Similarly, the bacteria enhance viral infection by altering the host's immune response, up-regulation of adhesion proteins, and activation of viral proteins. During co-infection, respiratory bacterial and viral pathogens were found to adapt and co-exist in the airways of their survival and to benefit from each other, i.e., there is a cooperative existence between the two. This review comprehensively reviews the mechanisms involved in the synergistic/cooperativity relationship between viruses and bacteria and their interaction in clinically relevant respiratory infections.

Interferon signaling drives epithelial metabolic reprogramming to promote secondary bacterial infection

Clinical studies report that viral infections promote acute or chronic bacterial infections at multiple host sites. These viral-bacterial co-infections are widely linked to more severe clinical outcomes. In experimental models in vitro and in vivo, virus-induced interferon responses can augment host susceptibility to secondary bacterial infection. Here, we used a cell-based screen to assess 389 interferon-stimulated genes (ISGs) for their ability to induce chronic Pseudomonas aeruginosa infection. We identified and validated five ISGs that were sufficient to promote bacterial infection. Furthermore, we dissected the mechanism of action of hexokinase 2 (HK2), a gene involved in the induction of aerobic glycolysis, commonly known as the Warburg effect. We report that HK2 upregulation mediates the induction of Warburg effect and secretion of L-lactate, which enhances chronic P. aeruginosa infection. These findings elucidate how the antiviral immune response renders the host susceptible to secondary bacterial infection, revealing potential strategies for viral-bacterial co-infection treatment.

Metagenomic-based pathogen surveillance for children with severe pneumonia in pediatric intensive care unit

Background

Pneumonia is a significant cause of morbidity and mortality in children. Metagenomic next-generation sequencing (mNGS) has the potential to assess the landscape of pathogens responsible for severe pulmonary infection.

Methods

Bronchoalveolar lavage fluid (BALF) samples of 262 children with suspected pulmonary infections were collected from April 2019 to October 2021 in the Pediatric Intensive Care Unit (PICU) of Guangdong Women and Children Hospital. Both mNGS and conventional tests were utilized for pathogen detection.

Results

A total of 80 underlying pathogens were identified using both mNGS and conventional tests. Respiratory syncytial virus (RSV), Staphylococcus aureus and rhinovirus were the most frequently detected pathogens in this cohort. The incidence rate of co-infection was high (58.96%, 148/251), with bacterial-viral agents most co-detected. RSV was the main pathogen in children younger than 6 months of age, and was also commonly found in older pediatric patients. Rhinovirus was prevalent in children older than 6 months. Adenovirus and Mycoplasma pneumoniae were more prevalent in children older than 3 years than in other age groups. Pneumocystis jirovecii was detected in nearly 15% of children younger than 6 months. Besides, influenza virus and adenovirus were rarely found in 2020 and 2021.

Conclusions

Our study highlights the importance of using advanced diagnostic techniques like mNGS to improve our understanding of the microbial epidemiology of severe pneumonia in pediatric patients.

A Hypothesis-Generating Prospective Longitudinal Study to Assess the Relative Contribution of Common Respiratory Viruses to Severe Lower Respiratory Infections in Young Children

BACKGROUND

Respiratory viruses such as respiratory syncytial virus (RSV), influenza, parainfluenza and human metapneumovirus are well-established etiologies of acute lower respiratory tract infections (ALRIs; LRI-viruses). In contrast, adenovirus (AdV), rhinovirus/enterovirus (RV/EV) and seasonal human coronaviruses (CoV), collectively termed AdV/RV/CoV, are detected both in healthy children and children with ALRI.

METHODS

The methods include a prospective longitudinal case-control study, assessing the prevalence of LRI-viruses versus AdV/RV/CoV in ALRI [community-acquired alveolar pneumonia (CAAP) and bronchiolitis] during hospitalization (visit 1), 7-14 days (visit 2) and 28-35 days (visit 3) in 2-17-month-old children. Controls were 2-27-month-old children hospitalized for elective surgery during the same respiratory seasons.

RESULTS

We enrolled 99 infants (37 CAAP, 38 bronchiolitis and 24 controls) and obtained 211 nasopharyngeal swabs. Overall, 163 (77%) had greater than or equal to 1 viruses detected; RV/EV (n = 94; 45%) and RSV (n = 71; 34%) were the most frequently detected viruses. In CAAP, the overall LRI-virus prevalence was 78.4%, 32.4% and 5.4% in visits 1, 2 and 3, respectively; the respective rates in bronchiolitis were 73.7%, 34.5% and 8.0%. In controls, no LRI-viruses were detected. In contrast, the overall AdV/RV/CoV prevalence was high among controls (70.8%) and similar among CAAP (48.6%, 40.5% and 40.5%) and bronchiolitis (47.4, 58.6% and 64.0%) across visits.

CONCLUSIONS

Among ALRI cases, LRI-viruses dominated during the acute disease, with prevalence declining within 28-35 days, suggesting their causative role. In contrast, AdV/RV/CoV prevalence was similar during all 3 visits and in controls, suggesting that carriage of these viruses is common during the viral respiratory season. The current study is relatively small and of short duration; however, the findings are supported by other recent studies.

Nasopharyngeal detection of atypical bacteria by multiplex polymerase chain reaction panel in acutely ill children was associated with an increased risk of pneumonia

AIM

We aimed to assess whether detection of respiratory bacteria by multiplex polymerase chain reaction (PCR) testing associates with clinical outcomes in acutely ill children.

METHODS

This cross-sectional study enrolled children under the age of 18 with a suspected respiratory infection treated in a paediatric emergency department of Oulu University Hospital, Finland from January 2015 through December 2015. Nasopharyngeal samples were routinely analysed for 16 respiratory viruses and later, after storage, analysed with a multiplex PCR panel for seven respiratory bacteria.

RESULTS

At least one bacterial pathogen was detected in 600 out of the 1195 children (50%). The mean age was 3.3 (SD 3.7) years and 54% were boys. Atypical bacteria were associated with a risk of pneumonia (adjusted odds ratio [aOR] 14.1, 95% CI 3.98-50.1). Co-detection of rhinovirus with Streptococcus pneumoniae was not associated with risk of pneumonia (aOR 2.39, 95% CI 0.78-7.30). Detection of Streptococcus pneumoniae, Haemophilus influenzae or both was not associated with the risk of hospital admission or prescription of antibiotics.

CONCLUSION

Nasopharyngeal detection of atypical bacteria in acutely ill children was associated with a markedly increased risk of pneumonia. The clinical utility of wide testing for other respiratory bacteria needs further evaluation.

RSV infection does not induce EMT

Respiratory syncytial virus (RSV) infection does not cause severe disease in most of us despite suffering from multiple RSV infections in our lives. However, infants, young children, older adults, and immunocompromised patients are unfortunately vulnerable to RSV-associated severe diseases. A recent study suggested that RSV infection causes cell expansion, resulting in bronchial wall thickening in vitro. Whether the virus-induced changes in the lung airway resemble epithelial-mesenchymal transition (EMT) is still unknown. Here, we report that RSV does not induce EMT in three different in vitro lung models: the epithelial A549 cell line, primary normal human bronchial epithelial cells, and pseudostratified airway epithelium. We found that RSV increases the cell surface area and perimeter in the infected airway epithelium, which is distinct from the effects of a potent EMT inducer, TGF-β1-driven cell elongation-indicative of cell motility. A genome-wide transcriptome analysis revealed that both RSV and TGF-β1 have distinct modulation patterns of the transcriptome, which suggests that RSV-induced changes are distinct from EMT.

Different Pediatric Acute Care Settings Influence Bronchiolitis Management: A 10-Year Retrospective Study

Bronchiolitis is the main cause of hospitalization in infants. Diagnosis is clinical, and treatment is based on hydration and oxygen therapy. Nevertheless, unnecessary diagnostic tests and pharmacological treatments are still very common. This retrospective study aimed to evaluate whether the setting of bronchiolitis care influences diagnostic and therapeutic choices. The management of 3201 infants, referred to our Italian Tertiary Care Center for bronchiolitis between 2010 and 2020, was analyzed by comparing children discharged from the pediatric emergency department (PEDd group) undergoing short-stay observation (SSO group) and hospitalization. Antibiotic use in PEDd, SSO, and ward was 59.3% vs. 51.6% vs. 49.7%, respectively (p < 0.001); inhaled salbutamol was mainly administered in PEDd and during SSO (76.1% and 82.2% vs. 38.3% in ward; p < 0.001); the use of corticosteroids was higher during SSO and hospitalization (59.6% and 49.1% vs. 39.0% in PEDd; p < 0.001); inhaled adrenaline was administered mostly in hospitalized infants (53.5% vs. 2.5% in SSO and 0.2% in PEDd; p < 0.001); chest X-ray use in PEDd, SSO, and ward was 30.3% vs. 49.0% vs. 70.5%, respectively (p < 0.001). In a multivariate analysis, undergoing SSO was found to be an independent risk factor for the use of systemic corticosteroid and salbutamol; being discharged at home was found to be a risk factor for antibiotic prescription; undergoing SSO and hospitalization resulted as independent risk factors for the use of CXR. Our study highlights that different pediatric acute care settings could influence the management of bronchiolitis. Factors influencing practice may include a high turnover of PED medical staff, personal reassurance, and parental pressure.

Microbial and Immune Regulation of the Gut-Lung Axis during Viral-Bacterial Coinfection

Viral-bacterial coinfections of the respiratory tract have long been associated with worsened disease outcomes. Clinical and basic research studies demonstrate that these infections are driven via complex interactions between the infecting pathogens, microbiome, and host immune response, although how these interactions contribute to disease progression is still not fully understood. Research over the last decade shows that the gut has a significant role in mediating respiratory outcomes, in a phenomenon known as the "gut-lung axis." Emerging literature demonstrates that acute respiratory viruses can modulate the gut-lung axis, suggesting that dysregulation of gut-lung cross talk may be a contributing factor during respiratory coinfection. This review will summarize the current literature regarding modulation of the gut-lung axis during acute respiratory infection, with a focus on the role of the microbiome, secondary infections, and the host immune response.

Clinical practice guidelines: management of severe bronchiolitis in infants under 12 months old admitted to a pediatric critical care unit

PURPOSE

We present guidelines for the management of infants under 12 months of age with severe bronchiolitis with the aim of creating a series of pragmatic recommendations for a patient subgroup that is poorly individualized in national and international guidelines.

METHODS

Twenty-five French-speaking experts, all members of the Groupe Francophone de Réanimation et Urgence Pédiatriques (French-speaking group of paediatric intensive and emergency care; GFRUP) (Algeria, Belgium, Canada, France, Switzerland), collaborated from 2021 to 2022 through teleconferences and face-to-face meetings. The guidelines cover five areas: (1) criteria for admission to a pediatric critical care unit, (2) environment and monitoring, (3) feeding and hydration, (4) ventilatory support and (5) adjuvant therapies. The questions were written in the Patient-Intervention-Comparison-Outcome (PICO) format. An extensive Anglophone and Francophone literature search indexed in the MEDLINE database via PubMed, Web of Science, Cochrane and Embase was performed using pre-established keywords. The texts were analyzed and classified according to the Grading of Recommendations Assessment, Development and Evaluation (GRADE) methodology. When this method did not apply, an expert opinion was given. Each of these recommendations was voted on by all the experts according to the Delphi methodology.

RESULTS

This group proposes 40 recommendations. The GRADE methodology could be applied for 17 of them (3 strong, 14 conditional) and an expert opinion was given for the remaining 23. All received strong approval during the first round of voting.

CONCLUSION

These guidelines cover the different aspects in the management of severe bronchiolitis in infants admitted to pediatric critical care units. Compared to the different ways to manage patients with severe bronchiolitis described in the literature, our original work proposes an overall less invasive approach in terms of monitoring and treatment.

Characterization of longitudinal nasopharyngeal microbiome patterns in maternally HIV-exposed Zambian infants

Background: Previous studies of infants born to HIV-positive mothers have linked HIV exposure to poor outcomes from gastrointestinal and respiratory illnesses, and to overall increased mortality rates. The mechanism behind this is unknown, but it is possible that differences in the nasopharyngeal (NP) microbiome between HIV-unexposed and HIV-exposed infants could play a role in perpetuating some outcomes. Methods: We conducted a longitudinal analysis of 170 NP swabs of healthy HIV-exposed, uninfected (HEU; n=10) infants and their HIV(+) mothers and HIV-unexposed, uninfected (HUU; n=10) infants and their HIV(-) mothers. These swabs were identified from a sample library collected in Lusaka, Zambia between 2015 and 2016. Using 16S rRNA gene sequencing, we characterized the maturation of the microbiome over the first 14 weeks of life to determine what quantifiable differences exist between HEU and HUU infants, and what patterns are reflected in the mothers' NP microbiomes. Results: In both HEU and HUU infants, Staphylococcus and Corynebacterium began as primary colonizers of the NP microbiome but were in time replaced by Dolosigranulum, Streptococcus, Moraxella and Haemophilus. When studying differences between infants, the microbe Staphylococcus haemolyticus indicated a distinctive high association with HIV exposure at birth, even when accounting for the interaction between HIV exposure status and time of sampling. When comparing infants to their mothers with paired analyses, HEU infants’ NP microbiome composition was only slightly different from their HIV(+) mothers at birth or 14 weeks, including in their carriage of S. pneumoniae, H. influenzae, and S. haemolyticus. Conclusions: Our analyses indicate that the HEU infants in our study exhibit subtle differences in the NP microbial composition throughout the sampling interval. Given our results and the sampling limitations of our study, we believe that further research must be conducted in order to confidently understand the relationship between HIV exposure and infants’ NP microbiomes.

Bronchiolitis therapies and misadventures

Viral bronchiolitis, which is most commonly caused by an infection with the respiratory syncytial virus (RSV), can lead to respiratory difficulties in young children which may require hospitalization. Despite years of research and medical trials, the mainstay of bronchiolitis treatment remains supportive only. This review provides an overview of the history of different treatments for bronchiolitis, including those that failed, as well as new therapies that are under study. Future studies for the treatment of bronchiolitis should consider different age-groups, important subgroups (i.e., those with a prior history of wheezing, those with a family history of asthma and those with non-RSV viral etiologies) whose response to treatment may differ from that of the composite group.

Pathogens and Pathogenesis in Wheezing Diseases in Children Under 6

Few studies have comprehensively assessed the roles of cytokine production in wheezing pathogenesis. Therefore, we undertook this study to determine the association between wheezing episodes and cytokines, and to provide further information on this topic. Firstly, we retrospectively collected I176 children, including 122 subjects with first wheezing and 54 subjects with recurrent wheezing, to analyze the etiology and clinical characteristics of children with wheezing diseases. Then, we collected 52 children with wheezing diseases and 25 normal controls to detect the expression of interferon-γ (IFN-γ), interleukin-4 (IL-4), IFN-γ/IL-4, IL-17A, IL-17E, IgE, matrix metalloproteinase-3 (MMP-3), and MMP-9 in serum or plasma. The results showed that boys under 3 years old with history of allergies were more likely to develop wheezing diseases. In our cohort, M. pneumoniae caused a greater proportion of wheezing in children than expected. The expression of IgE [18.80 (13.65-31.00) vs. 17.9 (10.15-21.60)], IL-4 [24.00 (24.00-48.00) vs. 23.00 (9.50-27.00)], IFN-γ [70.59 (41.63-116.46) vs. 49.83 (29.58-81.74)], MMP3 [53.40 (20.02-128.2) vs. 30.90 (13.80-50.95)], MMP9 [148.10 (99.30-276.10) vs. 122.10 (82.20-162.35)], IL-17A [80.55 (54.46-113.08) vs. 61.11 (29.43-93.87)], and IL-17E [1.75 (0.66-2.77) vs. 1.19 (0.488-2.1615)] were significantly increased in the wheezing group (p<0.05) compared to normal controls, while the level of IFN-γ/IL-4 had no significant difference between the two groups (1.24 ± 1.88 vs 0.68 ± 0.74, p>0.05). There was altered cytokine production in children with wheezing diseases which was quite similar to asthma pathogenesis. Sex, age, pathogen infection, and inflammation in our study were also risk factors for wheezing diseases.

Epidemiology and Outcomes of Bacterial Coinfection in Hospitalized Children With Respiratory Viral Infections: A Single Center Retrospective Chart Review

OBJECTIVE

Children with viral respiratory illness are often suspected of having bacterial coinfection. This study was designed to determine the impact of bacterial coinfection on hospital course and outcomes and the rate of antimicrobial misuse.

METHODS

Single-center retrospective chart review, including all hospitalized children who had a respiratory viral panel sent within 48 hours of admission from January 2015 to December 2019. Patients who had a positive respiratory, urine, blood culture within 24 hours of admission were identified. Demographics, resource utilization, and outcomes were compared between the 2 groups.

RESULTS

This study included 2192 patients. Of those, 269 patients had positive bacterial cultures. Out of these cultures from 192 patients were identified as contaminants. True bacterial coinfection was 3.5% (77/2192). Almost 1/3 of admitted patients were prescribed empiric antimicrobials. Children with bacterial coinfection tended to be younger (median age 8.4 months vs 16.3 months, p &lt; 0.01) and had higher proportion of prematurity (23.3% vs 12.1%, p &lt; 0.01). Children with bacterial coinfection were more likely to require ICU admission (37.6% vs 23.9%, p &lt; 0.01) and intubation (28.5% vs 5.3 %, p &lt; 0.01). They had higher ICU (5.7 days vs 1.9 days, p &lt; 0.01) and hospital length of stay (4.0 days vs 2.0 days, p &lt; 0.01), higher mortality (2.6% vs 0.2%, p = 0.02), and a higher median cost of hospital care ($3774.44 vs $2424.49.90, p &lt; 0.01).

CONCLUSIONS

The rate of bacterial coinfection in hospitalized children with viral infections is very low, which contradicts the routine administration of empiric antimicrobials. Patients with coinfection require more hospital resources and have worse clinical outcomes.

The effect of Ma-Xin-Gan-Shi decoction on asthma exacerbated by respiratory syncytial virus through regulating TRPV1 channel

ETHNOPHARMACOLOGICAL RELEVANCE

The incidence and mortality of bronchial asthma are increasing, and respiratory syncytial virus (RSV) is widely regarded as the common cause of clinical exacerbation of asthma. Ma-Xing-Gan-Shi decoction (MXGSD), a classic traditional Chinese medicine prescription, is well-known for treating respiratory diseases, while the mechanism of effecting on RSV-exacerbated asthma remains to be explored.

AIM OF THE STUDY

In this study, we investigated the mechanism by which MXGSD exerts a protective effect on asthma exacerbated by RSV in vivo and in vitro.

MATERIALS AND METHODS

MXGSD is composed of four Chinese medicine, including Ephedra intermedia Schrenk & C.A.Mey. (herbaceous stem, 27g), Prunus armeniaca L. (dry seed, 27g), Glycyrrhiza uralensis Fisch. (radix and rhizome, 18g), and Gypsum fibrosum (main component: CaSO4·2H2O, 54g). In the present study, the exacerbated asthmatic mice model with the treatment of OVA plus RSV was replicated, and accompanied by the TMT proteomic analysis and further experimental investigations. Then, the protective effect of MXGSD (13.2, 6.6, 3.3 g/kg/d, 7d) on the mice treated by OVA plus RSV, and the mechanism of regulating TRPV1 was explored. In addition, the intracellular Ca2+ concentration of 16HBE cells pretreated with MXGSD medicated serum was also tested after stimulation with the TRPV1 agonist capsaicin.

RESULTS

The results suggested that MXGSD could reduce the levels of inflammation cells, airway hyperresponsiveness, and pathological damage of lung tissue. TMT quantitative proteomics analysis and further experimental exploration revealed that MXGSD could reduce the levels of IL-4, IL-13, PGE2, and SP in BAL and down-regulate the expression of TRPV1 mRNA and protein in lung tissue. Furthermore, 16HBE cells stimulated by capsaicin showed an increased intracellular Ca2+ concentration, while the pretreatment of MXGSD medicated serum could reduce it.

CONCLUSION

MSGSD showed a protective effect on RSV-exacerbated asthma, which may be related to its regulation of TRPV1 expression and reduction of Th2 cytokines and neurogenic inflammatory mediators. It may provide an objective basis and reference for the clinical application of MXGSD.

Risk factors for disease severity and increased medical resource utilization in respiratory syncytial virus (+) hospitalized children: A descriptive study conducted in four Belgian hospitals

Background

We aimed to provide regional data on clinical symptoms, medical resource utilization (MRU), and risk factors for increased MRU in hospitalized respiratory syncytial virus (RSV)-infected Belgian pediatric population.

Methods

This prospective, multicenter study enrolled RSV (+) hospitalized children (aged ≤5y) during the 2013–2015 RSV seasons. RSV was diagnosed within 24h of hospitalization. Disease severity of RSV (+) patients was assessed until discharge or up to maximum six days using a Physical Examination Score (PES) and a derived score based on ability to feed, dyspnea and respiratory effort (PES3). MRU (concomitant medications, length of hospitalization [LOH], and oxygen supplementation) was evaluated. Kaplan-Meier survival analysis was performed to compare MRU by age and presence of risk factors for severe disease. Association between baseline covariates and MRU was analyzed using Cox regression models.

Results

In total, 75 children were included, Median (range) age was 4 (0–41) months, risk factors were present in 18.7%, and early hospitalization (≤3 days of symptom onset) was observed in 57.3% of patients. Cough (100%), feeding problems (82.2%), nasal discharge (87.8%), and rales and rhonchi (82.2%) were frequently observed. Median (range) LOH and oxygen supplementation was 5 (2–7) and 3 (1–7) days. Oxygen supplementation, bronchodilators, and antibiotics were administered to 58.7%, 64.0%, and 41.3% of the patients, respectively. Age <3 months and baseline total PES3 score were associated with probability and the duration of receiving oxygen supplementation. LOH was not associated with any covariate.

Conclusion

RSV is associated with high disease burden and MRU in hospitalized children. Oxygen supplementation but not length of hospitalization was associated with very young age and the PES3 score. These results warrant further assessment of the PES3 score as a predictor for the probability of receiving and length of oxygen supplementation in RSV hospitalized children.

Registration

NCT02133092

Repeated-Dose Toxicity, Biodistribution, and Shedding Assessments With a ChAd155 Respiratory Syncytial Virus Vaccine Candidate Evaluated in Rabbits and Rats

Respiratory syncytial virus (RSV) is a leading cause of acute lower respiratory tract infections (LRTI) in infants, and toddlers and vaccines are not yet available. A pediatric RSV vaccine (ChAd155-RSV) is being developed to protect infants against RSV disease. The ChAd155-RSV vaccine consists of a recombinant replication-deficient chimpanzee-derived adenovirus (ChAd) group C vector engineered to express the RSV antigens F, N, and M2-1. The local and systemic effects of three bi-weekly intramuscular injections of the ChAd155-RSV vaccine was tested in a repeated-dose toxicity study in rabbits. After three intramuscular doses, the ChAd155-RSV vaccine was considered well-tolerated. Changes due to the vaccine-elicited inflammatory reaction/immune response were observed along with transient decreases in platelet count without physiological consequences, already reported for other adenovirus-based vaccines. In addition, the biodistribution and shedding of ChAd155-RSV were also characterized in two studies in rats. The distribution and persistence of the ChAd155-RSV vaccine candidate was consistent with other similar adenovector-based vaccines, with quantifiable levels of ChAd155-RSV observed at the injection site (muscle) and the draining lymph nodes up to 69 days post administration. The shedding results demonstrated that ChAd155-RSV was generally not detectable in any secretions or excreta samples. In conclusion, the ChAd155-RSV vaccine was well-tolerated locally and systemically.

Bronchiolitis Management and Unnecessary Antibiotic Use Across 3 Canadian PICUs

OBJECTIVES

To describe the patient characteristics, clinical management, and infectious etiology in critically ill children with bronchiolitis. The secondary objective was to determine the association between antibiotic use and hospital length of stay among patients without concomitant bacterial infections.

METHODS

Retrospective cohort study including patients ≤2 years old with bronchiolitis admitted to 3 Canadian pediatric intensive care units between 2016 and 2018.

RESULTS

We included 372 patients with a median age of 2.1 months (interquartile range 1.2-6.6) and Pediatric Risk of Mortality III score 3.0 (interquartile range 0-3.0). Initial ventilatory management included high flow nasal cannula (28.2%) and noninvasive positive pressure ventilation (53.7%), of which 41.9% and 87.5%, respectively, did not require escalation of ventilatory support. Chest radiographs (81.7%) and respiratory virus testing (95.4%) were performed in most patients; 14.0% received systemic steroids. Respiratory syncytial virus was detected in 61.3% patients, and 7.5% had a culture-positive concomitant bacterial infection. Of 258 (69.4%) patients with a viral infection, only 45.3% received antibiotics. In this group, antibiotic use beyond 72 hours was not associated with hospital length of stay (ratio 1.14, 95% confidence interval 0.97-1.34).

CONCLUSIONS

High flow nasal canulae and noninvasive ventilation are commonly used in severe bronchiolitis. Despite contrary evidence, steroids and antibiotics were also frequently used. Evidence-based guidelines specific to children with severe bronchiolitis are needed to improve the care delivered to this patient population.

Risk factors and incidence of invasive bacterial infection in severe bronchiolitis: the RICOIB prospective study

Background

Bacterial infection (BI), both community-acquired (CA-BI) and hospital-acquired (HAI), might present as a severe complication in patients with bronchiolitis. This study aimed to describe BI in children with severe bronchiolitis, and to define risk factors for BI.

Methods

This was a prospective, descriptive study that included infants admitted to the pediatric intensive care unit (PICU) due to bronchiolitis between 2011 and 2017. The BROSJOD score was calculated to rate the severity of bronchiolitis.

Results

Inclusion of 675 patients, with a median age of 47 days (IQR 25–99). 175 (25.9%) patients developed BI, considered HAI in 36 (20.6%). Patients with BI had higher BROSJOD score, PRISM III, and required invasive mechanical ventilation and inotropic support more frequently (p < 0.001). BI was independently associated with BROSJOD higher than 12 (OR 2.092, 95%CI 1.168–3.748) CA-BI was associated to BROSJOD > 12 (OR 2.435, 95%CI 1.379–4.297) and bacterial co-infection (OR 2.294 95%CI 1.051–5.008). Concerning HAI, an independent association was shown with mechanical ventilation longer than 7 days (OR 5.139 95%CI 1.802–14.652). Infants with BI had longer PICU and hospital stay (p < 0.001), Mortality was higher in patients with HAI.

Conclusions

A quarter of infants with severe bronchiolitis developed BI. A BROSJOD > 12 may alert the presence of CA-BI, especially pneumonia. Patients with BI have higher morbidity and mortality.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12887-022-03206-4.

Pathogenesis of Respiratory Viral and Fungal Coinfections

Individuals suffering from severe viral respiratory tract infections have recently emerged as "at risk" groups for developing invasive fungal infections. Influenza virus is one of the most common causes of acute lower respiratory tract infections worldwide. Fungal infections complicating influenza pneumonia are associated with increased disease severity and mortality, with invasive pulmonary aspergillosis being the most common manifestation. Strikingly, similar observations have been made during the current coronavirus disease 2019 (COVID-19) pandemic. The copathogenesis of respiratory viral and fungal coinfections is complex and involves a dynamic interplay between the host immune defenses and the virulence of the microbes involved that often results in failure to return to homeostasis. In this review, we discuss the main mechanisms underlying susceptibility to invasive fungal disease following respiratory viral infections. A comprehensive understanding of these interactions will aid the development of therapeutic modalities against newly identified targets to prevent and treat these emerging coinfections.

Respiratory Pathogen Detection in Pediatric Patients Intubated for Presumed Infection

OBJECTIVES

Respiratory syncytial virus (RSV) in pediatric patients has been associated with low risk of concomitant bacterial infection. However, in children with severe disease, it occurs in 22% to 50% of patients. As viral testing becomes routine, bacterial codetections are increasingly identified in patients with non-RSV viruses. We hypothesized, among patients intubated for respiratory failure secondary to suspected infection, there are similar rates of codetection between RSV and non-RSV viral detections.

METHODS

This retrospective chart review, conducted over a 5-year period, included all patients younger than 2 years who required intubation secondary to respiratory failure from an infectious etiology in a single pediatric emergency department. Patients intubated for noninfectious causes were excluded.

RESULTS

We reviewed 274 patients, of which 181 had positive viral testing. Of these, 48% were RSV-positive and 52% were positive for viruses other than RSV. Codetection of bacteria was found in 76% (n = 65; 95% confidence interval [CI], 66%, 84%) of RSV-positive patients and 66% (n = 63, 95% CI: 57%, 76%) of patients positive with non-RSV viruses. Among patients with negative viral testing, 33% had bacterial growth on lower respiratory culture. Male sex was the only patient-related factor associated with increased odds of codetection (odds ratio [OR], 2.2; 95% CI, 1.08-4.38). The odds of codetection between RSV-positive patients and non-RSV viruses were not significantly different (OR, 1.3; 95% CI, 0.62-2.71).

CONCLUSIONS

Bacterial codetection is common and not associated with anticipated patient-related factors or with a specific virus. These results suggest consideration of empiric antibiotics in infants with respiratory illness requiring intubation.

Respiratory syncytial virus: from pathogenesis to potential therapeutic strategies

Respiratory syncytial virus (RSV) is one of the most important viral pathogens causing respiratory tract infection in infants, the elderly and people with poor immune function, which causes a huge disease burden worldwide every year. It has been more than 60 years since RSV was discovered, and the palivizumab monoclonal antibody, the only approved specific treatment, is limited to use for passive immunoprophylaxis in high-risk infants; no other intervention has been approved to date. However, in the past decade, substantial progress has been made in characterizing the structure and function of RSV components, their interactions with host surface molecules, and the host innate and adaptive immune response to infection. In addition, basic and important findings have also piqued widespread interest among researchers and pharmaceutical companies searching for effective interventions for RSV infection. A large number of promising monoclonal antibodies and inhibitors have been screened, and new vaccine candidates have been designed for clinical evaluation. In this review, we first briefly introduce the structural composition, host cell surface receptors and life cycle of RSV virions. Then, we discuss the latest findings related to the pathogenesis of RSV. We also focus on the latest clinical progress in the prevention and treatment of RSV infection through the development of monoclonal antibodies, vaccines and small-molecule inhibitors. Finally, we look forward to the prospects and challenges of future RSV research and clinical intervention.

Nasopharyngeal Codetection of H. influenzae and S. pneumoniae and Respiratory Syncytial Virus Disease Outcomes in Children

BACKGROUND

The role of nasopharyngeal bacteria on RSV disease has been underestimated. We measured the frequency and quantitative detection of potentially pathogenic bacteria in the upper respiratory tract of infants with RSV infection over seven respiratory seasons, and their impact on clinical outcomes.

METHODS

Children <2 years old with mild (outpatients; n=115) or severe (inpatients; n=566) RSV infection, and matched healthy controls (n=161) were prospectively enrolled. Nasopharyngeal samples were obtained for RSV, S. pneumoniae, S. aureus, M. catarrhalis, and H. influenzae detection and quantitation by PCR. Multivariable models were constructed to identify variables predictive of severe disease.

RESULTS

S. pneumoniae, H. influenzae, and M. catarrhalis, but not S. aureus, were detected more frequently in RSV-infected children (84%) than healthy controls (46%; p<0.001). Detection of S. pneumoniae and/or H. influenzae was associated with fever, more frequent antibiotic treatment, worse radiologic findings, and higher neutrophil counts (p<0.01). In adjusted analyses S. pneumoniae/H. influenzae co-detection was associated with greater odds (OR; 95% CI) of hospitalization (2.25 [1.07-4.74), higher disease severity scores (1.93 [1.14-3.26]), prolonged oxygen administration (2.23 [1.01-4.91]), and longer hospitalization (2.53 [1.33-4.79]).

CONCLUSIONS

Nasopharyngeal co-detection of S. pneumoniae and H. influenzae in infants with RSV infection is associated with increased disease severity.

RSV pneumonia with or without bacterial co-infection among healthy children

BACKGROUND

Respiratory syncytial virus (RSV) is a common cause of childhood pneumonia, but there is limited understanding of whether bacterial co-infections affect clinical severity.

METHODS

We conducted a retrospective cohort study at National Taiwan University Hospital from 2010 to 2019 to compare clinical characteristics and outcomes between RSV with and without bacterial co-infection in children without underlying diseases, including length of hospital stay, intensive care unit (ICU) admission, ventilator use, and death.

RESULTS

Among 620 inpatients with RSV pneumonia, the median age was 1.33 months (interquartile range, 0.67-2 years); 239 (38.6%) under 1 year old; 366 (59.0%) males; 201 (32.4%) co-infected with bacteria. The three most common bacteria are Streptococcus pneumoniae, Staphylococcus aureus and Haemophilus influenzae. The annually seasonal analysis showed that spring and autumn were peak seasons, and September was the peak month. Compared with single RSV infection, children with bacterial co-infection were younger (p = 0.021), had longer hospital stay (p < 0.001), needed more ICU care (p = 0.02), had higher levels of C-reactive protein (p = 0.009) and more frequent hyponatremia (p = 0.013). Overall, younger age, bacterial co-infection (especially S. aureus), thrombocytosis, and lower hemoglobin level were associated with the risk of requiring ICU care.

CONCLUSION

RSV related bacterial co-infections were not uncommon and assoicated with ICU admission, especially for young children, and more attention should be given. For empirical antibacterial treatment, high-dose amoxicillin-clavulanic acid or ampicillin-sulbactam was recommended for non-severe cases; vancomycin and third-generation cephalosporins were suggested for critically ill patients requiring ICU care.

Antimicrobial Consumption among 66 Acute Care Hospitals in Catalonia: Impact of the COVID-19 Pandemic

Background: Antimicrobials have been widely used during the COVID-19 pandemic. This study aimed to analyze the impact of the COVID-19 pandemic on the antimicrobial consumption of 66 hospitals in Catalonia. Methods: Adult antibacterial and antimycotic consumption was calculated as defined daily doses (DDD)/100 bed-days and DDD/100 discharges. Firstly, overall and ICU consumption in 2019 and 2020 were compared. Secondly, observed ICU 2020 consumptions were compared with non-COVID-19 2020 estimated consumptions (based on the trend from 2008–2019). Results: Overall, antibacterial consumption increased by 2.31% and 4.15% DDD/100 bed-days and DDD/100 discharges, respectively. Azithromycin (105.4% and 109.08% DDD/100 bed-days and DDD/100 discharges, respectively) and ceftriaxone (25.72% and 27.97% DDD/100 bed-days and DDD/100 discharges, respectively) mainly accounted for this finding. Likewise, antifungal consumption increased by 10.25% DDD/100 bed-days and 12.22% DDD/100 discharges, mainly due to echinocandins or amphotericin B. ICU antibacterial and antimycotic consumption decreased by 1.28% and 4.35% DDD/100 bed-days, respectively. On the contrary, antibacterial and antifungal use, expressed in DDD/100 discharges, increased by 23.42% and 19.58%. Azithromycin (275.09%), ceftriaxone (55.11%), cefepime (106.35%), vancomycin (29.81%), linezolid (31.28%), amphotericin B (87.98%), and voriconazole (96.17%) use changed the most. Observed consumption of amphotericin B, azithromycin, caspofungin, ceftriaxone, vancomycin, and voriconazole were higher than estimated values. Conclusions: The consumption indicators for most antimicrobials deviated from the expected trend pattern. A worrisome increase in antibacterial and antifungal consumption was observed in ICUs in Catalonia.

Severity of bronchiolitis in infants is associated with their parents' tobacco habit

The aim of this study was to investigate the effect of tobacco smoke exposure among severely pediatric ICU patients. A prospective epidemiological observational study was conducted among children with bronchiolitis younger than 2 years of age admitted to the Pediatric Intensive Care Unit of Children's University Hospital La Paz during the October 2017 to March 2018 outbreak. On admission, parents were asked whether they smoked. In children who required invasive mechanical ventilation, endotracheal aspirate was collected at the time of intubation. A total of 102 patients with bronchiolitis were studied. Among these, 14 (47%) of 30 infants whose parents smoked required invasive mechanical ventilation vs. 14 (19%) of 72 whose parents were nonsmokers (p = 0.007). Among patients on invasive mechanical ventilation, 10 (71%) of 14 infants with secondhand smoke exposure presented pulmonary bacterial superinfection vs. 3 (21%) of 14 in the unexposed (p = 0.012).Conclusion: Secondhand smoke exposure is an additional high risk for pulmonary bacterial superinfection and invasive mechanical ventilation in infants with severe acute bronchiolitis What is known: •Environmental tobacco smoke exposure is known to be an important risk factor for childhood lower respiratory tract infections. •Tobacco smoke makes structural changes in the respiratory tract and reduces the immune response. What in new: •Secondhand smoke exposure showed to be associated with the increased need and duration of invasive mechanical ventilation, and pediatric intensive care length of stay. •Tobacco smoke exposure is an additional risk factor for the presence of bacteria in the endotracheal aspirate.

Respiratory syncytial virus and airway microbiota - A complex interplay and its reflection on morbidity

The immunopathology of respiratory syncytial virus (RSV) infection varies considerably, severe disease occurring only in a minority of the affected children. The variability of the clinical presentation is in part explained by viral and environmental factors but, in infants and young children, disease severity is certainly linked to the physiologic immaturity of the innate and adaptive immune system. There is evidence that the maturation of the host immune response is positively influenced by the composition of the nasopharyngeal microbiome that, promoting an efficient reaction, can counteract the predisposition to develop viral respiratory infections and lower the risk of disease severity. However, interaction between the nasopharyngeal microbiota and respiratory viruses can be bidirectional since microbial dysbiosis may also represent a reflection of the disease-induced alterations of the local milieu. Moreover, viruses like RSV can also increase the virulence of potential pathogens in nasopharynx, a main reservoir of bacteria, and therefore promote their spread to the lower airways causing superinfection. Moreover, if negative changes in microbial community composition in early life may constitute a heightened risk toward severe RSV respiratory infection, on the contrary specific groups of microorganisms seem to be associated with protection. A better understanding into the potential negative and positive role of the different nasopharyngeal bacterial species on RSV infection may improve primary prevention and possibly care of this highly contagious disorder.

Neutrophils in respiratory viral infections

Viral respiratory infections are a common cause of severe disease, especially in infants, people who are immunocompromised, and in the elderly. Neutrophils, an important innate immune cell, infiltrate the lungs rapidly after an inflammatory insult. The most well-characterized effector mechanisms by which neutrophils contribute to host defense are largely extracellular and the involvement of neutrophils in protection from numerous bacterial and fungal infections is well established. However, the role of neutrophils in responses to viruses, which replicate intracellularly, has been less studied. It remains unclear whether and, by which underlying immunological mechanisms, neutrophils contribute to viral control or confer protection against an intracellular pathogen. Furthermore, neutrophils need to be tightly regulated to avoid bystander damage to host tissues. This is especially relevant in the lung where damage to delicate alveolar structures can compromise gas exchange with life-threatening consequences. It is inherently less clear how neutrophils can contribute to host immunity to viruses without causing immunopathology and/or exacerbating disease severity. In this review, we summarize and discuss the current understanding of how neutrophils in the lung direct immune responses to viruses, control viral replication and spread, and cause pathology during respiratory viral infections.

Bacterial and Viral Coinfections with the Human Respiratory Syncytial Virus

The human respiratory syncytial virus (hRSV) is one of the leading causes of acute lower respiratory tract infections in children under five years old. Notably, hRSV infections can give way to pneumonia and predispose to other respiratory complications later in life, such as asthma. Even though the social and economic burden associated with hRSV infections is tremendous, there are no approved vaccines to date to prevent the disease caused by this pathogen. Recently, coinfections and superinfections have turned into an active field of study, and interactions between many viral and bacterial pathogens have been studied. hRSV is not an exception since polymicrobial infections involving this virus are common, especially when illness has evolved into pneumonia. Here, we review the epidemiology and recent findings regarding the main polymicrobial infections involving hRSV and several prevalent bacterial and viral respiratory pathogens, such as Staphylococcus aureus, Pseudomonas aeruginosa, Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, Klebsiella pneumoniae, human rhinoviruses, influenza A virus, human metapneumovirus, and human parainfluenza viruses. As reports of most polymicrobial infections involving hRSV lack a molecular basis explaining the interaction between hRSV and these pathogens, we believe this review article can serve as a starting point to interesting and very much needed research in this area.

RSV attenuates epithelial cell restitution by inhibiting actin cytoskeleton-dependent cell migration

The airway epithelium's ability to repair itself after injury, known as epithelial restitution, is an essential mechanism enabling the respiratory tract's normal functions. Respiratory Syncytial Virus (RSV) is the leading cause of lower respiratory tract infections worldwide. We sought to determine whether RSV delays the airway epithelium wound repair process both in vitro and in vivo. We found that RSV infection attenuated epithelial cell migration, a step in wound repair, promoted stress fiber formation, and mediated assembly of large focal adhesions (FA). Inhibition of Rho kinase (ROCK), a master regulator of actin function, reversed these effects. There was increased RhoA and phospho-myosin light chain (pMLC2) following RSV infection. In vivo, mice were intraperitoneally inoculated with naphthalene to induce lung injury, followed by RSV infection. RSV infection delayed re-epithelialization. There were increased concentrations of pMLC2 in day 7 naphthalene plus RSV animals which normalized by day 14. This study suggests a key mechanism by which RSV infection delays wound healing.

Balancing precision versus cohort transcriptomic analysis of acute and recovery phase of viral bronchiolitis

Viral infections affecting the lower respiratory tract place enormous burdens on hospitals. As neither vaccines nor antiviral agents exist for many viruses, understanding risk factors and outcomes in each patient using minimally invasive analysis, such as blood, can lead to improved health care delivery. A cohort of PAXgene RNA sequencing of infants admitted with moderate or severe acute bronchiolitis and respiratory syncytial virus were compared with case-control statistical analysis and cohort-based outlier mapping for precision transcriptomics. Patients with severe bronchiolitis had signatures connected to the immune system, interferon signaling, and cytokine signaling, with marked sex differences in XIST, RPS4Y1, KDM5D, and LINC00278 for severity. Several patients had unique secondary infections, cytokine activation, immune responses, biological pathways, and immune cell activation, highlighting the need for defining patient-level transcriptomic signatures. Balancing relative contributions of cohort-based biomarker discoveries with patient's biological responses is needed to understand the totality of mechanisms of adverse outcomes in viral bronchiolitis.

Predictive factors of continuous negative extrathoracic pressure management failure in children with moderate to severe respiratory syncytial virus infection

Continuous negative extrathoracic pressure (CNEP) might be beneficial for children with severe respiratory tract infections. However, there are no available data on the predictors of its failure among individuals with respiratory syncytial virus (RSV) infections. Here, we conducted a retrospective cohort study between October 1, 2015 and October 31, 2018 in hospitalized children with moderate to severe symptoms of respiratory syncytial virus (RSV) infections. We divided 45 children requiring CNEP ventilation with a non-fluctuating negative pressure of − 12 cm H₂O into two groups. They were classified based on improvement or deterioration of their respiratory disorder under CNEP ventilation (responder group: n = 27, failure group: n = 18). Based on the univariate analysis, the responder and failure groups significantly differed in terms of median age, days elapsed from RSV onset to the initiation of CNEP, white blood cell count (WBC), titer of venous pCO₂, body temperature at admission, and modified Wood-Downes Score (mWDS) 6 h after initiating CNEP. Based on a logistic regression analysis adjusted for age < 1 year upon admission, less than 5 days elapsed from RSV onset to the initiation of CNEP, not high value of WBC and body temperature at admission, and high values of mWDS 6 h after initiating CNEP were found to be significant independent risk factors for CNEP ventilation failure. The former two variables were associated with less failure (odds ratio was approximately 5), and the latter two variables are associated with more failure (odds ratio was approximately 8–9). Thus, CNEP could be a valid option for children with moderate to severe RSV infections, especially in those who were aged > 1 year, and specific clinical and laboratory findings.

Reverse genetics systems for contemporary isolates of respiratory syncytial virus enable rapid evaluation of antibody escape mutants

Human respiratory syncytial virus (RSV) is the leading cause of acute lower respiratory infection in children under 5 y of age. In the absence of a safe and effective vaccine and with limited options for therapeutic interventions, uncontrolled epidemics of RSV occur annually worldwide. Existing RSV reverse genetics systems have been predominantly based on older laboratory-adapted strains such as A2 or Long. These strains are not representative of currently circulating genotypes and have a convoluted passage history, complicating their use in studies on molecular determinants of viral pathogenesis and intervention strategies. In this study, we have generated reverse genetics systems for clinical isolates of RSV-A (ON1, 0594 strain) and RSV-B (BA9, 9671 strain) in which the full-length complementary DNA (cDNA) copy of the viral antigenome is cloned into a bacterial artificial chromosome (BAC). Additional recombinant (r) RSVs were rescued expressing enhanced green fluorescent protein (EGFP), mScarlet, or NanoLuc luciferase from an additional transcription unit inserted between the P and M genes. Mutations in antigenic site II of the F protein conferring escape from palivizumab neutralization (K272E, K272Q, S275L) were investigated using quantitative cell-fusion assays and rRSVs via the use of BAC recombineering protocols. These mutations enabled RSV-A and -B to escape palivizumab neutralization but had differential impacts on cell-to-cell fusion, as the S275L mutation resulted in an almost-complete ablation of syncytium formation. These reverse genetics systems will facilitate future cross-validation efficacy studies of novel RSV therapeutic intervention strategies and investigations into viral and host factors necessary for virus entry and cell-to-cell spread.

Passive Immunoprophylaxis against Respiratory Syncytial Virus in Children: Where Are We Now?

Respiratory syncytial virus (RSV) represents the main cause of acute respiratory tract infections in children worldwide and is the leading cause of hospitalization in infants. RSV infection is a self-limiting condition and does not require antibiotics. However hospitalized infants with clinical bronchiolitis often receive antibiotics for fear of bacteria coinfection, especially when chest radiography is performed due to similar radiographic appearance of infiltrate and atelectasis. This may lead to unnecessary antibiotic prescription, additional cost, and increased risk of development of resistance. Despite the considerable burden of RSV bronchiolitis, to date, only symptomatic treatment is available, and there are no commercially available vaccines. The only licensed passive immunoprophylaxis is palivizumab. The high cost of this monoclonal antibody (mAb) has led to limiting its prescription only for high-risk children: infants with chronic lung disease, congenital heart disease, neuromuscular disorders, immunodeficiencies, and extreme preterm birth. Nevertheless, it has been shown that the majority of hospitalized RSV-infected children do not fully meet the criteria for immune prophylaxis. While waiting for an effective vaccine, passive immune prophylaxis in children is mandatory. There are a growing number of RSV passive immunization candidates under development intended for RSV prevention in all infants. In this review, we describe the state-of-the-art of palivizumab's usage and summarize the clinical and preclinical trials regarding the development of mAbs with a better cost-effectiveness ratio.

Unveiling the Risk Period for Death After Respiratory Syncytial Virus Illness in Young Children Using a Self-Controlled Case Series Design

BACKGROUND

Respiratory syncytial virus (RSV)-related acute lower respiratory infection is an important cause of death in infants and young children. However, little is known about the risk period for RSV-related deaths after presentation to health services with an RSV illness.

METHODS

Using the Scottish national mortality database, we identified deaths from respiratory/circulatory causes (hereafter "respiratory/circulatory deaths") in young children aged <5 years during 2009-2016, whose medical history and records of laboratory-confirmed RSV infections were obtained by linking the mortality database to the national surveillance data set and the Scottish Morbidity Record. We used a self-controlled case series (SCCS) design to evaluate the relative incidence of deaths with respiratory/circulatory deaths in the first year after an RSV episode. We defined the risk interval as the first year after the RSV episode, and the control interval as the period before and after the risk interval until 5 years after birth. Age-adjusted incidence ratio and attributable fraction were generated using the R software package SCCS.

RESULTS

We included 162 respiratory/circulatory deaths, of which 36 occurred in children with a history of laboratory-confirmed RSV infection. We found that the mortality risk decreased with time after the RSV episode and that the risk was statistically significant for the month after RSV illness. More than 90% of respiratory/circulatory deaths occurring within 1 week after the RSV episode were attributable to RSV (attributable fraction, 93.9%; 95% confidence interval, 77.6%-98.4%), compared with about 80% of those occurring 1 week to 1 month after RSV illness (80.3%; 28.5%-94.6%).

CONCLUSIONS

We found an increased risk of death in the first month after an RSV illness episode leading to healthcare attendance. This provides a practical cutoff time window for community-based surveillance studies estimating RSV-related mortality risk. Further studies are warranted to assess the mortality risk beyond the first month after RSV illness episode.

Streptococcus pneumoniae serotype 22F infection in respiratory syncytial virus infected neonatal lambs enhances morbidity

Respiratory syncytial virus (RSV) is the primary cause of viral bronchiolitis resulting in hospitalization and a frequent cause of secondary respiratory bacterial infection, especially by Streptococcus pneumoniae (Spn) in infants. While murine studies have demonstrated enhanced morbidity during a viral/bacterial co-infection, human meta-studies have conflicting results. Moreover, little knowledge about the pathogenesis of emerging Spn serotype 22F, especially the co-pathologies between RSV and Spn, is known. Here, colostrum-deprived neonate lambs were divided into four groups. Two of the groups were nebulized with RSV M37, and the other two groups were mock nebulized. At day three post-RSV infection, one RSV group (RSV/Spn) and one mock-nebulized group (Spn only) were inoculated with Spn intratracheally. At day six post-RSV infection, bacterial/viral loads were assessed along with histopathology and correlated with clinical symptoms. Lambs dually infected with RSV/Spn trended with higher RSV titers, but lower Spn. Additionally, lung lesions were observed to be more frequent in the RSV/Spn group characterized by increased interalveolar wall thickness accompanied by neutrophil and lymphocyte infiltration and higher myeloperoxidase. Despite lower Spn in lungs, co-infected lambs had more significant morbidity and histopathology, which correlated with a different cytokine response. Thus, enhanced disease severity during dual infection may be due to lesion development and altered immune responses rather than bacterial counts.

Use of procalcitonin and C-reactive protein in the diagnosis of bacterial infection in infants with severe bronchiolitis

The objective was to evaluate the use of procalcitonin (PCT) and C-reactive protein (CRP) for the diagnosis of bacterial infection in bronchiolitis patients. A prospective, single-centre, descriptive, and comparative observational study was carried out on patients with severe bronchiolitis admitted to the paediatric intensive care unit (PICU), from January 2011 to July 2017. Two cohorts were compared: patients with invasive bacterial infection (IBI) and patients with no bacterial infection (NBI). We included 675 patients, 399 of whom were males (59.1%), with median age of 47 days (IQR 25-100.3). Of them, 181 patients were diagnosed with IBI (26.8%). Seventy-two had sepsis (10.7%), 106 had pneumonia (15.7%), and 41 had a urinary tract infection (6.1%). PCT and CRP values were significantly higher in patients with IBI. ROC curves compared the ability of PCT and CRP to diagnose IBI at admission, 24 h, and 48 h. PCT showed a better AUC for diagnosing IBI, with statistically significant differences at all time points (p < 0.001). The best PCT cut-off for IBI diagnosis at admission was 1.4 ng/mL, with a sensitivity of 69% (95% CI 58.4-74.9) and a specificity of 91% (95% CI 88.1-92.5). Procalcitonin showed a better AUC for diagnosing both sepsis and pneumonia, which makes it an excellent predictor.Conclusion: We present PCT as a novel test in comparison with the traditional CRP screening test to discern which bronchiolitis patients have IBI. We highlight the importance of PCT for the diagnosis of pneumonia and sepsis, as it proved to be more sensitive and specific than CRP, with statistically significant differences. What is Known: • Bronchiolitis should be treated with antibiotics only when a bacterial infection is present. • The rate of antibiotic prescription in severe bronchiolitis is extremely high, so diagnostic tools are needed. What is New: • PCT is a good biomarker to discern which bronchiolitis patients have IBI, specially for pneumonia and sepsis diagnoses. It is more sensitive and specific than CRP, with statistically significant differences. • Implementation of PCT cut-off values may prevent unnecessary antibiotic use.

Respiratory syncytial virus infection exacerbates pneumococcal pneumonia via Gas6/Axl-mediated macrophage polarization

Patients with respiratory syncytial virus (RSV) infection exhibit enhanced susceptibility to subsequent pneumococcal infections. However, the underlying mechanisms involved in this increased susceptibility remain unclear. Here, we identified potentially novel cellular and molecular cascades triggered by RSV infection to exacerbate secondary pneumococcal pneumonia. RSV infection stimulated the local production of growth arrest-specific 6 (Gas6). The Gas6 receptor Axl was crucial for attenuating pneumococcal immunity in that the Gas6/Axl blockade fully restored antibacterial immunity. Mechanistically, Gas6/Axl interaction regulated the conversion of alveolar macrophages from an antibacterial phenotype to an M2-like phenotype that did not exhibit antibacterial activity, and the attenuation of caspase-1 activation and IL-18 production in response to pneumococcal infection. The attenuated IL-18 production failed to drive both NK cell-mediated IFN-γ production and local NO and TNF-α production, which impair the control of bacterial infection. Hence, the RSV-mediated Gas6/Axl activity attenuates the macrophage-mediated protection against pneumococcal infection. The Gas6/Axl axis could be a potentially novel therapeutic target for RSV-associated secondary bacterial infection.