Risk factors for carbapenem-resistant Acinetobacter baumannii (CRAB) bloodstream infections and related mortality in critically ill patients with CRAB colonization.

Background: Among MDR bacteria, carbapenem-resistant Acinetobacter baumannii (CRAB) is a major concern due to the limited therapeutic options. During the COVID-19 pandemic, a worrying increase in the spread of CRAB infections was reported. Objectives: The study assessed the risk factors for CRAB bloodstream infection (BSI) in patients admitted to the ICU with CRAB colonization, and the related mortality risk factors. Methods: We conducted a single-centre, observational, prospective study; all consecutive patients with CRAB colonization admitted to the ICU of a tertiary hospital in Rome from January 2021 to September 2022 were included in the study. Univariate and multivariate analyses were performed to investigate BSI and mortality risk factors. Results: Overall, 129 patients were included in the study; 57 (44%) out of these developed BSI. In our study population, at the multivariable analysis the Charlson comorbidity index (CCI) (P = 0.026), COVID-19 (P < 0.001), multisite colonization (P = 0.016) and the need for mechanical ventilation (P = 0.024) were risk factors independently associated with BSI development. Furthermore, age (P = 0.026), CCI (P < 0.001), septic shock (P = 0.001) and Pitt score (P < 0.001) were independently associated with mortality in the BSI patients. Instead, early appropriate therapy (P = 0.002) and clinical improvement within 72 h (P = 0.011) were shown to be protective factors. Conclusions: In critically ill patients colonized by CRAB, higher CCI, multisite colonization and the need for mechanical ventilation were identified as risk factors for BSI onset. These predictors could be useful to identify patients at highest risk of BSI.

First case of persistent Stenotrophomonas maltophilia bacteraemia due to septic thrombosis successfully treated with a cefiderocol-containing regimen.

INTRODUCTION: There is scarce evidence in literature of what should be the best antimicrobial treatment for bloodstream infections (BSIs) sustained by Stenotrophomonas maltophilia, a peculiar pathogen that intrinsically withstands to most of the available antibiotics. RESULTS AND CONCLUSION: Here, we describe a challenging case of a persistent S. maltophilia BSI due to septic thrombosis successfully treated with the addition of the novel siderophore cephalosporin cefiderocol to an only partially effective levofloxacin regimen. Additionally, an intra-lock therapy with trimethoprim/sulfamethoxazole was selected as a strategy to prevent recurrence of infection since complete source control was not possible. The serum bactericidal assay was also used to corroborate the in vivo efficacy of the adopted combination therapy.

Common Microbial Genital Infections and Their Impact on the Innate Immune Response to HPV in Cervical Cells.

The persistence of high-risk (HR) human papillomavirus (HPV) genotypes is a prerequisite of cervical cancer. It is not clear whether and how bacterial vaginosis (BV) and sexually transmitted infections (STIs) cause higher rates of persistent HPV infection. This study aimed to characterize mucosal innate immunity to HPV, comparing different conditions. Specifically, expression levels of genes coding for Toll-like receptors (TLR)7 and 9, several type III Interferon-related genes (IFNL1, 2, 3, their specific receptor subunit IFNLR1, and the IFN-stimulated gene ISG15). Chemokines CCL5 and CCL20 were measured in cervical cells positive, or not, for HPV, BV, and STIs. HPV DNA was detected in 51/120 (42.5%) enrolled women, two/third were HR-HPV genotypes. More than 50% of samples were BV- and/or STI-positive. HPV-positive women had BV, but not other STIs, more frequently than the HPV-negative. TLR9 and IFNL1 mRNAs were expressed in the LR, but much less in the HR HPV infection. Enhanced levels of TLR9, TLR7, IFNL2, and IFNLR1 were observed in HPV-positive women with BV and STI. TLR9-increased expression was associated with HPV persistence in previous studies; hence, bacterial coinfections may enhance this risk. Prospective measurements of type III IFNs and IFNLR1 are warranted to evaluate whether this response may act as a double-edged sword in infected epithelia.

The non-functional ACE2 isoform, but not the SARS-CoV-2 receptor, is induced as an interferon-stimulated gene, in SARS-CoV-2 infected adults.

The recently discovered truncated, non-functional, ACE2 transcript (dACE2), but not the full-length ACE2 (f-lACE2), is induced by IFNs in differentiated airway cells. We measured expression of both ACE2 isoforms in SARS-CoV-2 positive and negative subjects, in relation to Interferon-stimulated genes. A significant activation of dACE2 transcript was found, in SARS-CoV-2 positive adults either hospitalized or not, showing a positive correlation with ISG15; f-lACE2 expression was weakly activated and not ISG-related. We confirmed a specific activation of dACE2 transcript in nasopharyngeal cells, related to the mucosal IFN response.

Comparison by Age of the Local Interferon Response to SARS-CoV-2 Suggests a Role for IFN-ε and -ω.

Children generally develop a mild disease after SARS-CoV-2 infection whereas older adults are at risk of developing severe COVID-19. Recent transcriptomic analysis showed pre-activated innate immunity in children, resulting in a more effective anti-SARS-CoV-2 response upon infection. To further characterize age-related differences, we studied type I and III interferon (IFN) response in SARS-CoV-2 infected and non-infected individuals of different ages. Specifically, levels of expression of type I (IFN-α, -ß, -ε and -ω), type III (IFN-λ1, -λ2 and -λ3) IFNs and of the IFN-stimulated genes, ISG15 and ISG56 were quantified in nasopharyngeal cells from diagnostic swabs. Basal transcription of type I/III IFN genes was highest among children and decreased with age. Among SARS-CoV-2-infected individuals, only IFN-ε and -ω levels were significantly higher in children and young adults whereas ISGs were overexpressed in infected adults. The occurrence of symptoms in children and the need for hospitalization in adults were associated to higher transcription of several IFN genes. Starting from a pre-activated transcription level, the expression of type I and III IFNs was not highly up-regulated in children upon SARS-CoV-2 infection; young adults activated IFNs' transcription at intermediate levels whereas older adults were characterized by higher ISGs and lower IFN-ε and -ω relative expression levels. Overall, our findings contribute to recognize components of a protective IFN response as a function of age, in the context of SARS-CoV-2 infection.

High prevalence of Merkel cell polyomavirus is associated with dysregulation in transcript levels of TLR9 and type I IFNs in a large cohort of CF patients from the Italian (Lazio) reference center for cystic fibrosis.

Merkel cell polyomavirus (MCPyV) has been detected in respiratory specimens including those from Cystic Fibrosis (CF) patients, raising questions about its immunological and clinical relevance in the respiratory tract. MCPyV might promote an inappropriate antiviral response contributing to a chronic inflammatory response and resulting in detrimental effects in CF. Respiratory samples (n = 1138) were randomly collected from respiratory tract of CF patients (n = 539) during July 2018-October 2019. MCPyV-DNA detection was performed by real time PCR and positive samples were characterized by sequencing of the NCCR genomic region. The transcript levels of Toll-like receptor 9 (TLR9) and type I interferon (IFN-I) genes (IFNα, IFNß and IFNε) were examined by real-time RT-PCR assays. MCPyV-DNA was detected in 268 out of 1138 respiratory specimens (23.5%) without any difference in the prevalence of MCPyV-DNA according to age, gender or bacteriological status of CF individuals. Thirteen out of 137 CF patients remained positive for MCPyV-DNA over the time (a median follow-up period of 8.8 months). Detection of MCPyV-DNA in respiratory specimens was not associated with the occurrence of exacerbation events. Both MCPyV positive adolescents (11-24 years) and adults (≥25 years) had lower mRNA levels of TLR9, IFNß, IFNε and IFNα than the negative patients of the same age group, while MCPyV positive children produced increased levels of TLR9 and IFN-I genes (p < 0.05 for TLR9, IFNß, IFNε) with respect to the negative ones. There were significant differences in TLR9 levels (p < 0.01), but not in those of IFNs, between MCPyV-DNA positive and negative patients with S. aureus, P. aeruginosa or both. Overall, these results indicate that MCPyV-DNA is frequently detected in the respiratory samples of CF patients and might influence the expression levels of IFN-related genes in an age dependent manner. The concomitant detection of MCPyV together with S. aureus and/or P. aeruginosa correlated with alterations in TLR9 levels suggesting that virus-bacteria coinfections might contribute to affect antiviral immunity in CF patients.

Analysis of serum microRNAs and rs2910164 GC single-nucleotide polymorphism of miRNA-146a in COVID-19 patients.

Alteration of micro-RNAs (miRNAs) expression, including miRNA-122a, -146a and -205 family members, can have profound effects on inflammatory and IFN pathways (miRNA-146a), known as hallmarks of COVID-19. SARS-CoV-2-infected patients were recruited at Policlinico Umberto I Hospital of Sapienza University of Rome (Italy). MiRNA-122a, -146a, -205 and IFI27 (Interferon Alpha Inducible Protein 27) levels were screened in SARS-CoV-2 patients (n = 14) and healthy controls (n = 10) by real-time RT-PCR assays. Then, miRNA-146a rs2910164 GC single-nucleotide polymorphism (SNP) was genotyped in a larger group of COVID-19 patients (n = 129), and its relationship with severe disease [Intensive Care Unit (ICU) support or survival/death] was assessed. SARS-CoV-2-positive patients had increased PCR, D-Dimer and Fibrinogen levels compared to healthy controls (p < .05 for all measurements). MiRNA-122a and -146a serum levels were upregulated in COVID-19 patients (miRNA-122a: p = .002; miRNA-146a: p < .001). Decreased IFI27 levels were observed in COVID-19 patients with higher miRNA-146a levels (p = .047). Moreover, miRNA-146a rs2910164 C/G genotypes distributions were similar in COVID-19 patients and in validated European healthy subjects (n = 37,214). MiRNA-146a SNP was not associated with severe COVID-19 outcome (ICU or death). MiRNA-122a and -146a levels were elevated in SARS-CoV-2 infected patients, with miRNA-146a upregulation possibly contributing to IFN pathways dysregulation (e.g., reduced IFI27 levels) observed in severe COVID-19, although there is no evidence for the involvement of rs2910164 SNP.

First COVID-19 lockdown resulted in most respiratory viruses disappearing among hospitalised children, with the exception of rhinoviruses.

AIM: Emergency room admissions have decreased globally during the COVID-19 pandemic, particularly for respiratory diseases. We evaluated hospital admissions for respiratory diseases in the first year of the Italian pandemic and compared them with the corresponding period in 2016-2017. METHODS: The study was carried out at the Sapienza University in Rome, Italy, and covered 9 March to 28 February 2020-2021 and 2016-2017. We tested 85 hospitalised children who were negative for the virus that causes COVID-19 in 2020-2021 and compared them with 476 hospitalised children from 2016-2017, as we had also tested nasal washing samples for 14 respiratory viruses during that period. RESULTS: Hospitalisations for acute respiratory tract infections were 82.2% lower in 2020-2021 than 2016-2017. The respiratory syncytial virus (RSV) and several other viruses were detected less frequently during the pandemic. An extraordinary finding was that rhinoviruses remained seasonal. In 2020-2021, we detected a virus in 54.1% of the hospitalised children: rhinoviruses in 41, RSV in 4 and other viruses in 1. This was significantly lower than the 71.6% in 2016-2017: RSV in 130, rhinoviruses in 128 and other viruses in 83. CONCLUSION: Pandemic measures dramatically reduced childhood respiratory infections, particularly RSV, but were less effective at reducing rhinoviruses.

KI and WU Polyomavirus in Respiratory Samples of SARS-CoV-2 Infected Patients.

Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) has been declared a global pandemic. Our goal was to determine whether co-infections with respiratory polyomaviruses, such as Karolinska Institutet polyomavirus (KIPyV) and Washington University polyomavirus (WUPyV) occur in SARS-CoV-2 infected patients. Oropharyngeal swabs from 150 individuals, 112 symptomatic COVID-19 patients and 38 healthcare workers not infected by SARS-CoV-2, were collected from March 2020 through May 2020 and tested for KIPyV and WUPyV DNA presence. Of the 112 SARS-CoV-2 positive patients, 27 (24.1%) were co-infected with KIPyV, 5 (4.5%) were positive for WUPyV, and 3 (2.7%) were infected simultaneously by KIPyV and WUPyV. Neither KIPyV nor WUPyV DNA was detected in samples of healthcare workers. Significant correlations were found in patients co-infected with SARS-CoV-2 and KIPyV (p < 0.05) and between SARS-CoV-2 cycle threshold values and KIPyV, WUPyV and KIPyV and WUPyV concurrently detected (p < 0.05). These results suggest that KIPyV and WUPyV may behave as opportunistic respiratory pathogens. Additional investigations are needed to understand the epidemiology and the prevalence of respiratory polyomavirus in COVID-19 patients and whether KIPyV and WUPyV could potentially drive viral interference or influence disease outcomes by upregulating SARS-CoV-2 replicative potential.

Alteration of type I interferon response is associated with subclinical atherosclerosis in virologically suppressed HIV-1-infected male patients.

Given human immunodeficiency virus-1 (HIV-1)-infected patients have alterations in the type I interferon (IFN-I) pathway and are also at elevated risk of atherosclerosis, we evaluated IFN-I response and subclinical cardiovascular disease (CVD) association in HIV-1-infected patients. Transcript levels of IFN-α/ß and IFN-stimulated gene 56 (ISG56) were evaluated by RT/real-time PCR in peripheral blood mononuclear cells collected from asymptomatic HIV-1-positive male patients at high risk of developing CVD (n = 34) and healthy subjects (n = 21). Stenosis degree (≥ or <50%), calcium volume score, calcium Agatston score, and myocardial extracellular volume were examined by coronary computerized tomography scan. Carotid intima-media thickness (cIMT), Framingham risk score, atherosclerotic cardiovascular disease (ASCVD) score, and risk score developed by data collection on adverse effects of anti-HIV drugs (D:A:D) were also measured. Increased IFN-α, IFN-ß, and ISG56 levels were observed in all HIV-1-infected males compared to healthy controls (p < .001 for all genes analyzed). HIV-1-infected patients with a stenosis degree ≥50% showed a higher Framingham risk score (p = .019), which was correlated with IFN-ß and ISG56 levels. HIV-1-infected males with enhanced IFN-I levels and stenosis displayed a higher ASCVD calculated risk (p = .011) and D:A:D score (p = .004). Also, there was a trend toward higher IFN-α and ISG56 mRNA levels in HIV-1-positive patients with an increased cIMT (p > .05). Dysregulation of IFN-I response might participate in the pathogenesis of HIV-1-associated CVD.

Viral community acquired pneumonia at the emergency department: Report from the pre COVID-19 age.

The role of viruses in community acquired pneumonia (CAP) has been largely underestimated in the pre-coronavirus disease 2019 age. However, during flu seasonal early identification of viral infection in CAP is crucial to guide treatment and in-hospital management. Though recommended, the routine use of nasopharyngeal swab (NPS) to detect viral infection has been poorly scaled-up, especially in the emergency department (ED). This study sought to assess the prevalence and associated clinical outcomes of viral infections in patients with CAP during peak flu season. In this retrospective, observational study adults presenting at the ED of our hospital (Rome, Italy) with CAP from January 15th to February 22th, 2019 were enrolled. Each patient was tested on admission with Influenza rapid test and real time multiplex assay. Seventy five consecutive patients were enrolled. 30.7% (n = 23) tested positive for viral infection. Of these, 52.1% (n = 12) were H1N1/FluA. 10 patients had multiple virus co-infections. CAP with viral infection did not differ for any demographic, clinic and laboratory features by the exception of CCI and CURB-65. All intra-ED deaths and mechanical ventilations were recorded among CAP with viral infection. Testing only patients with CURB-65 score ≥2, 10 out of 12 cases of H1N1/FluA would have been detected saving up to 40% tests. Viral infection occurred in one-third of CAP during flu seasonal peak 2019. Since not otherwise distinguishable, NPS is so far the only reliable mean to identify CAP with viral infection. Testing only patients with moderate/severe CAP significantly minimize the number of tests.

ACE2 expression is related to the interferon response in airway epithelial cells but is that functional for SARS-CoV-2 entry?

In vitro interferon (IFN)α treatment of primary human upper airway basal cells has been shown to drive ACE2 expression, the receptor of SARS-CoV-2. The protease furin is also involved in mediating SARS-CoV-2 and other viral infections, although its association with early IFN response has not been evaluated yet. In order to assess the in vivo relationship between ACE2 and furin expression and the IFN response in nasopharyngeal cells, we first examined ACE2 and furin levels and their correlation with the well-known marker of IFNs' activation, ISG15, in children (n = 59) and adults (n = 48), during respiratory diseases not caused by SARS-CoV-2. A strong positive correlation was found between ACE2 expression, but not of furin, and ISG15 in all patients analyzed. In addition, type I and III IFN stimulation experiments were performed to examine the IFN-mediated activation of ACE2 isoforms (full-length and truncated) and furin in epithelial cell lines. Following all the IFNs treatments, only the truncated ACE2 levels, were upregulated significantly in the A549 and Calu3 cells, in particular by type I IFNs. If confirmed in vivo following IFNs' activation, the induction of the truncated ACE2 isoform only would not enhance the risk of SARS-CoV-2 infection in the respiratory tract.

SARS-CoV-2 Entry Genes Expression in Relation with Interferon Response in Cystic Fibrosis Patients.

The expression rate of SARS-CoV-2 entry genes, angiotensin-converting enzyme 2 (ACE2), the main viral receptor and the proteases, furin and transmembrane serine protease 2 (TMPRSS2) in cystic fibrosis (CF) individuals is poorly known. Hence, we examined their levels in upper respiratory samples of CF patients (n = 46) and healthy controls (n = 45). Moreover, we sought to understand the interplay of type I interferon (IFN-I) with ACE2, furin and TMPRSS2 by evaluating their gene expression with respect to ISG15, a well-known marker of IFN activation, in upper respiratory samples and after ex vivo IFNß exposure. Lower ACE2 levels and trends toward the reduction of furin and TMPRSS2 were found in CF patients compared with the healthy controls; decreased ACE2 amounts were also detected in CF individuals with pancreatic insufficiency and in those receiving inhaled antibiotics. Moreover, there was a strong positive correlation between ISG15 and ACE2 levels. However, after ex vivo IFNß stimulation of nasopharyngeal cells, the truncated isoform (dACE2), recently demonstrated as the IFN stimulated one with respect to the full-length isoform (flACE2), slightly augmented in cells from CF patients whereas in those from healthy donors, dACE2 levels showed variable levels of upregulation. An altered expression of SARS-COV-2 entry genes and a poor responsiveness of dACE2 to IFN-I stimulation might be crucial in the diffusion of SARS-CoV-2 infection in CF.

Differential induction of type I and III interferon genes in the upper respiratory tract of patients with coronavirus disease 2019 (COVID-19).

The natural course of type I and III interferon (IFN) response in the respiratory tract of COVID-19 patients needs to be better defined. We showed that type I/III IFNs, IFN-regulatory factor 7 (IRF7), and IFN stimulated genes (ISGs), are highly expressed in the oropharyngeal cells of SARS-CoV-2 positive patients compared to healthy controls. Notably, the subgroup of critically-ill patients that required invasive mechanical ventilation had a general decrease in expression of IFN/ISG genes. Heterogeneous patterns of IFN-I/III response in the respiratory tract of COVID-19 patients may be associated to COVID-19 severity.

SARS-CoV-2 diagnostics in the virology laboratory of a University Hospital in Rome during the lockdown period.

Italy was one of the most affected nations by coronavirus disease 2019 outside China. The infections, initially limited to Northern Italy, spread to all other Italian regions. This study aims to provide a snapshot of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) epidemiology based on a single-center laboratory experience in Rome. The study retrospectively included 6565 subjects tested for SARS-CoV-2 at the Laboratory of Virology of Sapienza University Hospital in Rome from 6 March to 4 May. A total of 9995 clinical specimens were analyzed, including nasopharyngeal swabs, bronchoalveolar lavage fluids, gargle lavages, stools, pleural fluids, and cerebrospinal fluids. Positivity to SARS-CoV-2 was detected in 8% (527/6565) of individuals, increased with age, and was higher in male patients (P < .001). The number of new confirmed cases reached a peak on 18 March and then decreased. The virus was detected in respiratory samples, in stool and in pleural fluids, while none of gargle lavage or cerebrospinal fluid samples gave a positive result. This analysis allowed to gather comprehensive information on SARS-CoV-2 epidemiology in our area, highlighting positivity variations over time and in different sex and age group and the need for a continuous surveillance of the infection, mostly because the pandemic evolution remains unknown.

Differential toll like receptor expression in cystic fibrosis patients' airways during rhinovirus infection.

OBJECTIVES: Since an inappropriate and sustained activation of TLRs may contribute to a chronic inflammatory response resulting in detrimental effects in cystic fibrosis (CF) patients, we sought to examine whether HRV infection might alter the respiratory expression of TLRs according to the microbiological status of CF patients. METHODS: Respiratory samples were collected from the respiratory tract of CF patients (n = 294) over a period of 12 months. In addition to the usual microbiological investigation, HRV-RNA detection and typing were performed by RT-PCR and sequencing. HRV viral load and TLRs levels were measured by RT-Real Time PCR. RESULTS: HRV-RNA was detected in 80 out of 515 respiratory samples (15.5%) with a similar rate in all age groups (0-10 years, 11-24 years, ≥ 25 years). Patients infected with different HRV A, B and C species exhibited higher levels of TLR2, TLR4 and TLR8 as compared to HRV negative patients. Moreover, the expression level of TLR2, TLR4 and TLR8 correlated with high level of HRV viral load. HRV positive patients co-colonized by Staphylococcus aureus or Pseudomonas aeruginosa showed also enhanced amounts of TLR2 and TLR2/4-mRNAs expression respectively. In the case of presence of both bacteria, TLR2, TLR4, TLR8 and TLR9 levels are elevated in positive HRV patients. CONCLUSIONS: TLRs, especially TLR2 and TLR4, increased in HRV positive CF individuals and varies according to the presence of S. aureus, P. aeruginosa and both bacteria.

A single centre study of viral community-acquired pneumonia in children: No evidence of SARS-CoV-2 from October 2019 to March 2020.

Pneumonia is an important cause of morbidity and mortality in children. We described viral aetiologies, with particular interest in detecting SARS-CoV-2, in hospitalized pneumonia children. Human rhinovirus was the most frequently detected agent. No children tested positive for SARS-CoV-2. Our findings suggest that SARS-CoV-2 infection is rare in children and it was not circulating in Rome before COVID-19 outbreak.

Novel Variants of Respiratory Syncytial Virus A ON1 Associated With Increased Clinical Severity of Bronchiolitis.

BACKGROUND: A study of respiratory syncytial virus-A (RSV A) genotype ON1 genetic variability and clinical severity in infants hospitalized with bronchiolitis over 6 epidemic seasons (2012-2013 to 2017-2018) was carried out. METHODS: From prospectively enrolled term infants hospitalized for bronchiolitis, samples positive for RSV A ON1 (N = 139) were sequenced in the second half of the G gene. Patients' clinical data were obtained from medical files and each infant was assigned a clinical severity score. ANOVA comparison and adjusted multinomial logistic regression were used to evaluate clinical severity score and clinical parameters. RESULTS: The phylogenetic analysis of 54 strains showed 3 distinct clades; sequences in the last 2 seasons differed from previous seasons. The most divergent and numerous cluster of 2017-2018 strains was characterized by a novel pattern of amino acid changes, some in antigenic sites. Several amino acid changes altered predicted glycosylation sites, with acquisition of around 10 new O-glycosylation sites. Clinical severity of bronchiolitis increased in 2016-2017 and 2017-2018 and changed according to the epidemic seasons only. CONCLUSIONS: Amino acid changes in the hypervariable part of G protein may have altered functions and/or changed its immunogenicity, leading to an impact on disease severity.

Differential interferon gene expression in bronchiolitis caused by respiratory syncytial virus-A genotype ON1.

Bronchiolitis severity is determined by a complex interaction among viral replication and antiviral immunity. The current respiratory syncytial virus (RSV)-A, genotype ON1 demonstrated a high replicative capacity but seemed to be clinically less severe than the previously circulating RSV-A, NA1. To learn insights about ON1 innate immune response, we analyzed expression levels of type I/III interferon (IFN)-related genes in the respiratory mucosa of infants with RSV bronchiolitis. We enrolled RSV-positive bronchiolitis patients over 12 epidemic seasons at a university hospital in Rome. From nasopharyngeal washings' cells (46 positive to NA1, 47 to ON1 and 28 to RSV-B, genotype BA), the mRNA copy number of the type III IFN receptor (IFNLR1 and IL10RB subunits), and of the type I/III IFN-stimulated genes, MxA and ISG56, was calculated using the threshold cycle relative quantification method with respect to an invariant gene. Expression levels of type III IFN receptor subunits genes positively correlated to each other and did not differ in infants infected with different RSV genotypes. The ISGs levels also positively correlated between them but differed among groups. MxA levels were significantly higher in NA1-infected infants than in those with ON1 and BA; ISG56 expression was slightly higher in NA1 than in the other strains. Interestingly, a moderate negative correlation existed between viral load and both ISGs values in ON1-infected infants only. The reduced ISG levels elicited during infections with ON1 (and BA) may cause a weaker control of RSV replication and/or an inadequate host immune response which may impact the risk of respiratory sequelae.