Young infants display heterogeneous serological responses and extensive but reversible transcriptional changes following initial immunizations

Infants necessitate vaccinations to prevent life-threatening infections. Our understanding of the infant immune responses to routine vaccines remains limited. We analyzed two cohorts of 2-month-old infants before vaccination, one week, and one-month post-vaccination. We report remarkable heterogeneity but limited antibody responses to the different antigens. Whole-blood transcriptome analysis in an initial cohort showed marked overexpression of interferon-stimulated genes (ISGs) and to a lesser extent of inflammation-genes at day 7, which normalized one month post-vaccination. Single-cell RNA sequencing in peripheral blood mononuclear cells from a second cohort identified at baseline a predominantly naive immune landscape including ISGhi cells. On day 7, increased expression of interferon-, inflammation-, and cytotoxicity-related genes were observed in most immune cells, that reverted one month post-vaccination, when a CD8+ ISGhi and cytotoxic cluster and B cells expanded. Antibody responses were associated with baseline frequencies of plasma cells, B-cells, and monocytes, and induction of ISGs at day 7.

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.

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.

Donor-derived bacterial infections in lung transplant recipients in the era of multidrug resistance

OBJECTIVES

Our aim was to analyze the prevalence of multidrug-resistant bacterial infections in lung transplant donors and to evaluate its influence on donor-derived bacterial infections.

METHODS

We conducted a retrospective study of adult patients who underwent lung transplantation (2013-2016) at our hospital. Donor-derived bacterial infection was defined as the isolation of the same bacteria with identical antibiotic susceptibility patterns in the recipient and the perioperative cultures from the donor during the first month posttransplantation. We utilized a preventive antibiotic strategy adapted to the bacteria identified in donor cultures using systemic and nebulized antibiotics.

RESULTS

252 lung transplant recipients and 243 donors were included. In 138/243 (56.8%) donors, one bacterial species was isolated from at least one sample; graft colonization (118/243; 48.6%), blood cultures (5/243; 2.1%) and the contamination of preservation fluids (56/243; 23%). Multidrug-resistant bacteria were isolated from 12/243 (4.9%) donors; four Enterobacterales, four Stenotrophomonas maltophilia, three Pseudomonas aeruginosa and one methicillin-resistant Staphylococcus aureus. There was no transmission of these multidrug-resistant bacteria. Donor-derived infections, primarily tracheobronchitis due to non-MDR bacteria, were diagnosed in 7/253 (2.9%) recipients, with good clinical outcomes.

CONCLUSIONS

The lungs of donors colonized with multidrug-resistant bacteria may be safely used when recipients receive prompt tailored antibiotic treatment.

118. Nasopharyngeal (NP) Bacterial Detection in Infants With Respiratory Syncytial Virus (RSV) Infection: Impact on Clinical Outcomes

Background

Previous studies suggest that RSV increases NP bacterial colonization and may facilitate infection. However, the role of NP colonization with potentially pathogenic bacteria (PPB) in the pathogenesis of RSV bronchiolitis is not well understood. We sought to determine the frequency, type, and density of NP PPB detection in infants with RSV infection compared with healthy controls (HC), and its association with clinical outcomes.

Methods

Single-center, prospective study of previously healthy infants with RSV infection and age-matched HC. Inpatients (IP) were enrolled within 24 hours of hospitalization, outpatients (OP) at the ED or primary clinics and HC at well-child visits. RSV infection and the following PPB: [S. pneumoniae, M. catarrhalis, H. influenzae, and S. aureus] were detected and quantified by PCR. We compared demographic, clinical characteristics, and outcomes of care according to NP PPB detection.

Results

From 2010 to 2018, we enrolled 815 infants: 664 with RSV infection [IP, 560; OP, 104] and 151 HC. RSV+ OP (6.1 [3.7–10.7] months) and HC (6.9 [3.8–10.8] months) were older than IP (2.5 [1.4–5.4] months; P < 0.001). Identification of ≥1 PPB was 89% in RSV+ infants [IP, 88%; OP, 90%] versus 63% of HC (P < 0.0001). While H. influenzae or >1 PPB detection was higher in RSV infection (P < 0.001), S. aureus detection predominated in HC (P < 0.05; Figure 1). Frequency of S. pneumoniae detection was comparable between groups; however, S. pneumoniae loads were one log higher in RSV+ infants versus HC (P = 0.001) adjusted for antibiotic use. Differences in colonization rates remained different in RSV+ infants versus HC across age ranges (<3, 3–6, >6–12, and >12–24 months; Figure 2). Last, RSV patients (both IP and OP) with S. pneumoniae or H. influenzae detection had fever more frequently (70%–74% vs. 25%–47%; P < 0.0001), higher clinical disease severity scores (P = 0.01), and higher blood neutrophil counts (34%–36% vs. 16%–19%; P < 0.001), versus those with M. catarrhalis, S. aureus detection or PCR negative. In addition, NP detection of H. influenzae in RSV children was associated with higher frequency of atelectasis/consolidation by chest X-ray (P < 0.005).

Conclusion

These data suggest that NP colonization with PPB is high in infants with RSV infection independent of age, and that specific bacteria, namely S. pneumoniae and H. influenzae, are associated with enhanced clinical disease severity.

Disclosures

A. Leber, Nationwide Children’s Hospital: Research Contractor, Research support. O. Ramilo, Janssen Scientific Affairs, LLC: Consultant, Consulting fee. A. Mejias, Janssen: Grant Investigator and Scientific Advisor, Consulting fee and Research grant. Abbvie: CME talks, Speaker honorarium.

Interferon gene expression as marker of immune maturation and response to vaccination

Background

Interferons (IFN) play a major role in regulating innate and adaptive immune responses. Studies in adults and older children demonstrated significant correlations between IFN gene expression and antibody responses to influenza vaccines. However, there is still an incomplete understanding of the role of IFN in the ontogeny of the infant immune system and how they affect the immune response to vaccines in this population. Our objective with this study is to define longitudinal age-related changes in interferon gene expression and the changes induced by routine vaccinations.

Methods

We enrolled 2 cohorts of healthy children: 81 children aged &lt; 2 years evaluated at one-time point to assess age-dependent changes in IFN gene expression; and 47 &lt; 1 year olds evaluated at three times, before vaccination (day (d) 0) and d7 and d30 post-vaccination. Peripheral blood samples were collected to measure: (a) immune transcriptional profiles by microarrays; (b) immune cell populations by flow cytometry, and (c) antibody titers to PCV13, Hib and DTaP in the vaccination cohort.

Results

Analysis of first cohort demonstrated significant underexpression of IFN genes (n = 120) in infants aged &lt;6 months compared with those 12–24 months. By 9 months IFN expression was similar to the older children. IFN gene expression correlated with the numbers of neutrophils and monocytes across all age groups. The second cohort was evaluated at three time points (d0, d7, and d30) during routine vaccinations at 2, 6, and 12 months. We compared transcriptional profiles post-vaccination with d0 for each group and observed consistent overexpression of IFN-related genes at d7 in the three age groups. In 2-month-old infants, we observed significant correlations between IFN genes (TAP1, IFIT1/2/3, OASL and GBP1) at d0 (before vaccination) and increase in antibody titers of the three vaccines analyzed (r = 0.5–0.7; P &lt; 0.05). Among the top 15 genes who have the most significant correlations, eight are exclusively induced by type I IFN, six by type II IFN, and one is shared between the two types.

Conclusion

IFN gene expression at baseline is markedly reduced in infants &lt;6 months. Routine vaccines were associated with marked increased in IFN gene expression at 2, 6, and 12 months. Baseline IFN expression at 2 months correlated with antibody responses to vaccines.

Disclosures

O. Ramilo, Abbvie: Board Member, Consulting fee; Regeneron: Board Member, Consulting fee; Janssen: Board Member and Investigator, Consulting fee and Research grant; NIH: Grant Investigator, Research grant

Nasopharyngeal Microbiota, Host Transcriptome, and Disease Severity in Children with Respiratory Syncytial Virus Infection

RATIONALE

Respiratory syncytial virus (RSV) is the leading cause of acute lower respiratory tract infections and hospitalizations in infants worldwide. Known risk factors, however, incompletely explain the variability of RSV disease severity, especially among healthy children. We postulate that the severity of RSV infection is influenced by modulation of the host immune response by the local bacterial ecosystem.

OBJECTIVES

To assess whether specific nasopharyngeal microbiota (clusters) are associated with distinct host transcriptome profiles and disease severity in children less than 2 years of age with RSV infection.

METHODS

We characterized the nasopharyngeal microbiota profiles of young children with mild and severe RSV disease and healthy children by 16S-rRNA sequencing. In parallel, using multivariable models, we analyzed whole-blood transcriptome profiles to study the relationship between microbial community composition, the RSV-induced host transcriptional response, and clinical disease severity.

MEASUREMENTS AND MAIN RESULTS

We identified five nasopharyngeal microbiota clusters characterized by enrichment of either Haemophilus influenzae, Streptococcus, Corynebacterium, Moraxella, or Staphylococcus aureus. RSV infection and RSV hospitalization were positively associated with H. influenzae and Streptococcus and negatively associated with S. aureus abundance, independent of age. Children with RSV showed overexpression of IFN-related genes, independent of the microbiota cluster. In addition, transcriptome profiles of children with RSV infection and H. influenzae- and Streptococcus-dominated microbiota were characterized by greater overexpression of genes linked to Toll-like receptor and by neutrophil and macrophage activation and signaling.

CONCLUSIONS

Our data suggest that interactions between RSV and nasopharyngeal microbiota might modulate the host immune response, potentially affecting clinical disease severity.

Improved Sepsis Alert With a Telephone Call From the Clinical Microbiology Laboratory: A Clinical Trial

Early sepsis attention is a standard of care in many institutions and the role of different specialists is well recognized. However, the impact of a telephone call from a specialist in Clinical Microbiology upon blood cultures request has not been assessed to the best of our knowledge. We performed telephone calls followed by an interview with physicians and nurses in charge of adult patients (> 18 years old) whose blood cultures had just been received in the Microbiology Laboratory in a tertiary hospital. Patients were randomly classified in 2 different groups: group A (telephone call performed) and group B (no telephone call). At the end of the telephonic intervention, recommendations on the use of microbiology and biochemical tests as well as on the management and antibiotic therapy of sepsis were made if required. We included 300 patients. Of those fulfilling standard criteria of sepsis, 30.3% of the nurses and 50% of the physicians immediately recognized it. Advice to optimize the use of biochemical and microbiological tests was provided in 36% of the cases and to improve antimicrobial therapy in 57.6%. The median number of days of antibiotic use in groups A and B were, respectively, 6 days (IQR: 2-12) vs 9 days (IQR: 4-16) P = 0.008 and the median number of prescribed daily doses of antimicrobials (6 [IQR: 3-17] vs 10 [IQR: 5-22] P = 0.016) were lower in group A. We estimate a reduction, only in the use of antibiotic, of 1.8 million Euros per year. A telephone call with management advice, immediately after the arrival of blood cultures in the Microbiology Laboratory improves the recognition of sepsis and the use of diagnostic resources and reduces antimicrobial consumption and expenses.

Superiority of transcriptional profiling over procalcitonin for distinguishing bacterial from viral lower respiratory tract infections in hospitalized adults

BACKGROUND

Distinguishing between bacterial and viral lower respiratory tract infection (LRTI) remains challenging. Transcriptional profiling is a promising tool for improving diagnosis in LRTI.

METHODS

We performed whole blood transcriptional analysis in 118 patients (median age [interquartile range], 61 [50-76] years) hospitalized with LRTI and 40 age-matched healthy controls (median age, 60 [46-70] years). We applied class comparisons, modular analysis, and class prediction algorithms to identify and validate diagnostic biosignatures for bacterial and viral LRTI.

RESULTS

Patients were classified as having bacterial (n = 22), viral (n = 71), or bacterial-viral LRTI (n = 25) based on comprehensive microbiologic testing. Compared with healthy controls, statistical group comparisons (P < .01; multiple-test corrections) identified 3376 differentially expressed genes in patients with bacterial LRTI, 2391 in viral LRTI, and 2628 in bacterial-viral LRTI. Patients with bacterial LRTI showed significant overexpression of inflammation and neutrophil genes (bacterial > bacterial-viral > viral), and those with viral LRTI displayed significantly greater overexpression of interferon genes (viral > bacterial-viral > bacterial). The K-nearest neighbors algorithm identified 10 classifier genes that discriminated between bacterial and viral LRTI with a 95% sensitivity (95% confidence interval, 77%-100%) and 92% specificity (77%-98%), compared with a sensitivity of 38% (18%-62%) and a specificity of 91% (76%-98%) for procalcitonin.

CONCLUSIONS

Transcriptional profiling is a helpful tool for diagnosis of LRTI.

Vancomycin MICs do not predict the outcome of methicillin-resistant Staphylococcus aureus bloodstream infections in correctly treated patients

BACKGROUND

Recent studies have reported a greater probability of vancomycin treatment failure in methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infections caused by strains with a vancomycin MIC ≥ 1.5 mg/L. However, previous reports included patients treated without adjustments based on vancomycin serum levels and with different methods to evaluate MICs, which may render different results.

METHODS

Over a 5 year period (2005-09), vancomycin MICs were determined for 361 MRSA isolates recovered from 309 patients with bloodstream infection using microdilution and the Etest simultaneously. The relationship between the vancomycin MICs determined by each method was assessed. To assess the outcome of patients treated with vancomycin, 104 patients for whom serum vancomycin levels had been determined were selected.

RESULTS

The percentage of MRSA strains with MIC values ≥ 1.5 mg/L according to the Etest was 66.5% compared with only 3.6% according to microdilution. No correlation between mortality and any MIC value obtained with either method was observed, independently of the vancomycin serum levels measured.

CONCLUSIONS

There is a poor correlation between vancomycin MIC values obtained by microdilution and by Etest. No association between mortality rate and any MIC value was observed, not even in patients with suboptimal vancomycin trough serum levels. These data do not support replacing or complementing the standard microdilution test with the Etest for determination of MICs of vancomycin in microbiology laboratories.

Ventilator-associated pneumonia due to meticillin-resistant Staphylococcus aureus: risk factors and outcome in a large general hospital

BACKGROUND

Data about risk factors and impact on outcome of methicillin-resistant S. aureus (MRSA) in unselected patients with ventilator-associated pneumonia (VAP) are limited.

AIM

To assess predisposing factors and outcome of VAP due to MRSA in a large teaching institution.

METHODS

Prospective study carried out over four years in the three adult ICUs of our hospital. Patients with MRSA-VAP were compared with those with bacterial VAP due to other microorganisms.

FINDINGS

Overall, 474 episodes of bacterial VAP were collected. Significant differences between MRSA-VAP (111) and VAP due to other microorganisms (363) were found for median age (68 vs. 62 years), median APACHE II score (12 vs. 11), neurosurgery (5.4% vs. 13.8%), abdominal surgery (35% vs. 19%), prior treatment with any antibiotic (82.9% vs. 64.5%) and with imipenem (24% vs. 11%) at present admission before VAP, and pleural effusion (12% vs. 5%). Multivariate analysis adjusted for confounding factors showed that higher APACHE II score, prior treatment with any antibiotic and pleural effusion were independent risk factors for MRSA. As for treatment and outcome, the differences between MRSA-VAP and other VAP were inadequate empiric treatment (70% vs. 53%), median cost of antibiotics per episode (€974 vs. €726), and in-hospital mortality (60% vs. 47%). At multivariate analysis, however, MRSA was not found to be an independent risk factor for mortality.

CONCLUSION

MRSA is a common cause of VAP. Underlying conditions predispose to its high mortality.