CD38high/HLA-DR+CD8+ T lymphocytes display pathogen-specific expansion regardless of hemophagocytic lymphohistiocytosis.

The characteristic expansion of T CD38high/HLA-DR+CD8+ lymphocytes observed in hemophagocytic lymphohistiocytosis (HLH) and macrophage activation syndrome (MAS) proved able to distinguish HLH/MAS from sepsis and systemic juvenile idiopathic arthritis. However, the performance of this marker in differentiating HLH/MAS from other pediatric febrile conditions with similar clinical onset and yet entirely different treatments remains unexplored. CD38high/HLA-DR+CD8+ frequencies measured in the peripheral fresh blood of pediatric patients attended for suspicion of HLH/MAS were retrospectively recorded and clinical characteristics were retrieved. CD38high/HLA-DR+CD8+ frequencies in HLH/MAS patients (15 patients; median: 22.0%, IQR: 11.0-49.0%) were compared with those who presented febrile conditions other-than-HLH (28 patients; median: 13.0%, IQR: 3.9-28.7%; p = 0.24). HLH and non-HLH patients were subsequently regrouped based on the presence of an identified infection (22 patients; median: 27.0%, IQR: 15.2-72.1%) and compared with those without infections (21 patients; median: 7.6%, IQR: 3.7-24.3%; p = 0.0035). CD38high/HLA-DR+CD8+ percentages were significantly higher only in the infection group compared with the noninfection one, with a patent pathogen-specific expansion in Epstein-Barr virus primoinfection and visceral leishmaniasis regardless of the presence of HLH. CD38high/HLA-DR+CD8+ frequencies do not appear as an HLH-specific marker as they naturally expand in other clinical situations that are common in childhood and may mimic HLH initial presentation.

Impact of respiratory syncytial virus on older children: Exploring the potential for preventive strategies beyond the age of 2 years.

OBJECTIVE: Respiratory syncytial virus (RSV) causes significant lower respiratory tract infections (LRTIs) in infants and young children. Current prevention targets those under 2 years. This study aims to evaluate RSV patterns and severity in children older than 2 years and to explore the potential extension of preventive strategies to this demographic group. METHODS: An observational retrospective study at Meyer Children's Hospital (from October 2019 to March 2023) analyzed data from patients between 28 days and 18 years of age with RSV infection. Severity indicators and patient characteristics were compared between two age groups: under 2 years and 2 years and above. RESULTS: 584 infants and young children were hospitalized due to RSV infection. Epidemic seasons saw a rise in hospitalizations among children older than 2 years. Older children had higher comorbidity (41% versus 9% p=0.000) and prematurity (26% versus 14% p = 0.001) rates than those under 2 years. CONCLUSION: The study highlights the increased risk of severe RSV LRTIs in children older than 2 years and with prematurity or comorbidities, overlooked by current preventive measures. Prospective studies and cost-effectiveness analyses are needed to determine the necessity of targeted immunization for older children with specific risk factors, aiming to reduce RSV-related morbidity and mortality.

Epidemiology of respiratory syncytial virus in hospitalized children over a 9-year period and preventive strategy impact.

Background: Respiratory Syncytial Virus (RSV) is the primary cause of respiratory infections and hospitalizations in young children globally, leading to substantial disease burden and mortality. The aim of the present study was to review and provide updates on how the SARS-CoV-2 pandemic have significantly influenced RSV epidemiology on hospitalized children due to RSV infection. A potential impact of the available preventive strategies on the same population were provided. Methods: All children aged 0-6 years hospitalized at Meyer Children's Hospital IRCCS for RSV infection from September 2014 to March 2023 were retrospectively recorded. Seasonal trends before and after SARS-CoV-2 pandemic, age distribution, ICU admission and co-infections, comorbidities and prematurity were retrieved. Predictions on the number of hospitalizations avoided by the deployment of different preventive strategies were provided. Results: A total of 1,262 children with RSV infection were included in the study. The 70% of them had less than 1 year-of-age at the moment of hospitalization and almost 50% less than 3 months. In the post-pandemic seasons, a 317% increase in the number of hospitalizations was recorded with a significant increase in older children compared to the pre-pandemic seasons. ICU support was required for 22% of children, the majority of whom were under 3 months of age. Almost 16% of hospitalized children were born preterm and only 27% of hospitalized children had prior comorbidities. The rate of comorbidities among RSV hospitalized children increased with age. Nirsevimab prophylaxis could have prevented more than 46% of hospitalizations in this cohort. A preventive strategy addressing also children aged 7 months to 6 years of age with co-existing comorbidities would increase that rate above 57%. Discussion: The identification of RSV hospitalization-related features is informing the decision-maker for the deployment of the wisest preventive approach on a population scale.

Corrigendum: HLH as an additional warning sign of inborn errors of immunity beyond familial-HLH in children: a systematic review.

[This corrects the article DOI: 10.3389/fimmu.2024.1282804.].

Expanded Newborn Screening for Inborn Errors of Immunity: The Experience of Tuscany.

BACKGROUND: Inborn errors of immunity (IEIs) include 485 inherited disorders characterized by an increased susceptibility to life-threatening infectious diseases, autoimmunity, and malignant diseases with a high mortality rate in the first years of life. Severe combined immunodeficiency is the most severe of the IEIs, and its detection should be a primary goal in a newborn screening (NBS) program. The term "actionable" has recently been used for all IEIs with outcomes that can be demonstrably improved through early specialized intervention. OBJECTIVE: To evaluate the results of the expanded NBS strategy for IEIs in Tuscany Region (Italy), based on T-cell receptor excision circle, kappa recombining excision circle, and tandem mass-based assays. METHODS: This is a retrospective study collecting data from all infants born in Tuscany from October 10, 2018, to October 10, 2022. Tandem mass assay to identify adenosine deaminase and purine nucleoside phosphorylase deficiency, together with T-cell receptor excision circle and kappa recombining excision circle molecular analysis, was conducted on dried blood spot from the newborns' Guthrie Cards. A new dried blood spot and evaluation by an immunologist were carried out when the results of the first test were outside the diagnostic cutoffs. RESULTS: A total of 94,319 newborns were evaluated. Referral rates for T-cell recombining excision circles (0.031%) and kappa recombining excision circles (0.074%) in this study are in line with the data available in literature. The results from the expanded NBS strategy revealed an incidence rate of 1 per 9431 affected newborns. CONCLUSIONS: This work represents the first description of a sustainable and real-life-based expanded NBS program for IEIs with a high diagnostic incidence facilitating prompt management of identified patients.

Immunological Aspects of Kabuki Syndrome: A Retrospective Multicenter Study of the Italian Primary Immunodeficiency Network (IPINet).

Kabuki Syndrome (KS) is a multisystemic genetic disorder. A portion of patients has immunological manifestations characterized by increased susceptibility to infections and autoimmunity. Aiming to describe the clinical and laboratory immunological aspects of KS, we conducted a retrospective multicenter observational study on patients with KS treated in centers affiliated to the Italian Primary Immunodeficiency Network.Thirty-nine patients were enrolled, with a median age at evaluation of 10 years (range: 3 m-21y). All individuals had organ malformations of variable severity. Congenital heart defect (CHD) was present in 19/39 patients (49%) and required surgical correction in 9/39 (23%), with associated thymectomy in 7/39 (18%). Autoimmune cytopenia occurred in 6/39 patients (15%) and was significantly correlated with thymectomy (p < 0.002), but not CHD. Individuals with cytopenia treated with mycophenolate as long-term immunomodulatory treatment (n = 4) showed complete response. Increased susceptibility to infections was observed in 22/32 patients (69%). IgG, IgA, and IgM were low in 13/29 (45%), 13/30 (43%) and 4/29 (14%) patients, respectively. Immunoglobulin substitution was required in three patients. Lymphocyte subsets were normal in all patients except for reduced naïve T-cells in 3/15 patients (20%) and reduced memory switched B-cells in 3/17 patients (18%). Elevated CD3 + TCRαß + CD4-CD8-T-cells were present in 5/17 individuals (23%) and were correlated with hematological and overall autoimmunity (p < 0.05).In conclusion, immunological manifestations of KS in our cohort include susceptibility to infections, antibody deficiency, and autoimmunity. Autoimmune cytopenia is correlated with thymectomy and elevated CD3 + TCRαß + CD4-CD8-T-cells, and benefits from treatment with mycophenolate.

Severe A(H1N1)pdm09 influenza acute encephalopathy outbreak in children in Tuscany, Italy, December 2023 to January 2024.

A severe outbreak of influenza A(H1N1pdm09) infection in seven children (median age: 52 months) occurred between December 2023 and January 2024 in Tuscany, Italy. Clinical presentation ranged from milder encephalopathy to acute necrotizing encephalopathy (ANE) with coma and multiorgan failure; one child died. This report raises awareness for clinicians to identify and treat early acute encephalopathy caused by H1N1 influenza and serves as a reminder of severe presentations of influenza in young children and the importance of vaccination.

Dupilumab treatment of trichothiodystrophy in a child.

Trichothiodystrophy (TTD) is a rare congenital disorder caused by genetic mutations, leading to hair and skin abnormalities. We report successful treatment of a TTD case using dupilumab, a monoclonal antibody targeting IL-4Rα. The patient, a 7-year-old boy, exhibited significant improvement in skin and hair conditions, suggesting the potential of dupilumab as a therapeutic option for TTD. Further research is needed to elucidate its mechanism and efficacy in TTD treatment.

HLH as an additional warning sign of inborn errors of immunity beyond familial-HLH in children: a systematic review.

Background: Hemophagocytic Lymphohistiocytosis (HLH) is a rare and life-threatening condition characterized by a severe impairment of the immune homeostasis. While Familial-HLH (FHL) is a known cause, the involvement of other Inborn Errors of Immunity (IEI) in pediatric-HLH remains understudied. Objective: This systematic review aimed to assess the clinical features, triggers, laboratory data, treatment, and outcomes of pediatric HLH patients with IEI other than FHL (IEInotFHL), emphasizing the importance of accurate identification and management. Methods: A systematic search for studies meeting inclusion criteria was conducted in PubMed, EMBASE, MEDLINE, and Cochrane Central. Quality assessment was performed through JBI criteria. Results: A comprehensive search yielded 108 records meeting inclusion criteria, involving 178 patients. We identified 46 different IEI according to IUIS 2022 Classification. Combined immunodeficiencies, immune dysregulation disorders, and phagocyte defects were the IEI most frequently associated with HLH. In 75% of cases, HLH preceded the IEI diagnosis, often with an unrecognized history of severe infections. Triggers reflected the specific infection susceptibilities within IEI groups. Liver and central nervous system involvement were less common than in FHL cases. Treatment approaches and outcomes varied, with limited long-term follow-up data, limiting the assessment of therapeutic efficacy across IEI groups. Conclusion: A comprehensive evaluation encompassing immunological, infectious, and genetic aspects is essential in pediatric-HLH. Relying solely on FHL or EBV susceptibility disorders tests is insufficient, as diverse other IEI can contribute to HLH. Early recognition of HLH as a potential warning sign can guide timely diagnostic investigations and facilitate tailored therapeutic interventions for improved outcomes. Systematic review registration: https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=371425, PROSPERO, CRD42022371425.

Analysis of a Cohort of 165 Pediatric Patients with Human Bocavirus Infection and Comparison between Mono-Infection and Respiratory Co-Infections: A Retrospective Study.

INTRODUCTION: Human Bocavirus (HBoV) is mainly associated with respiratory tract infections. However, its role as respiratory pathogen is not fully understood for a high co-infection rate in symptomatic patients and a significant HBoV detection rate in asymptomatic subjects. This study aimed to describe a large cohort of children with HBoV infection and to compare HBoV mono-infection and co-infections. METHODS: We retrospectively reviewed data from 165 children admitted to Meyer Children's Hospital IRCCS from March 2022 to March 2023 with the diagnosis of HBoV infection, detected using Reverse Transcription qPCR from nasal swabs. Thereafter, we compared patients with HBoV mono-infection (Group A) and those with HBoV co-infections (Group B) in terms of disease severity, established by the length of stay (LOS), the requirement of Pediatric Intensive Care Unit (PICU), and advanced respiratory support (ARS). RESULTS: The median age was 1.5 years; 80% of patients presented with respiratory symptoms. The discharge rate from the emergency department (ED) within 24 h was 42.4%. Most cases (57.6%) were hospitalized, and 7.3% were admitted to PICU due to respiratory failure. Group A comprised 69 patients, and Group B 96 children (95% viral co-infections, 2% bacterial, 3% viral and bacterial). Group A and Group B were similar in hospitalization rate but differed significantly in LOS (median 3 vs. 5 days) and requirement of PICU admission (0 vs. 12 patients, p < 0.001). Patients with a respiratory disease history (17.5%) showed significantly longer LOS and more necessity of inhaled bronchodilator therapy. CONCLUSIONS: HBoV should be considered a relevant respiratory pathogen especially in viral co-infections. Patients with HBoV co-infections have a higher risk of necessitating advanced respiratory support with more PICU admission and longer LOS; a previous respiratory disease puts them at a higher risk of longer hospitalization.

Reshaping Our Knowledge: Advancements in Understanding the Immune Response to Human Respiratory Syncytial Virus.

Human respiratory syncytial virus (hRSV) is a significant cause of respiratory tract infections, particularly in young children and older adults. In this review, we aimed to comprehensively summarize what is known about the immune response to hRSV infection. We described the innate and adaptive immune components involved, including the recognition of RSV, the inflammatory response, the role of natural killer (NK) cells, antigen presentation, T cell response, and antibody production. Understanding the complex immune response to hRSV infection is crucial for developing effective interventions against this significant respiratory pathogen. Further investigations into the immune memory generated by hRSV infection and the development of strategies to enhance immune responses may hold promise for the prevention and management of hRSV-associated diseases.

Risk of thyroid neoplasms in patients with 22q11.2 deletion and DiGeorge-like syndromes: an insight for follow-up.

Introduction: The chromosome 22q11.2 deletion syndrome comprises phenotypically similar diseases characterized by abnormal development of the third and fourth branchial arches, resulting in variable combinations of congenital heart defects, dysmorphisms, hypocalcemia, palatal dysfunction, developmental or neuropsychiatric disorders, and impairment of the immune system due to thymic dysfunction. Other genetic syndromes, often called DiGeorge-like, share clinical and immunological features with 22q11.2 deletion syndrome. This syndrome has been rarely associated with malignancies, mainly hematological but also hepatic, renal, and cerebral. Rarely, malignancies in the head and neck region have been described, although no aggregate of data on the development of thyroid neoplasms in patients with this clinical phenotype has been conducted so far. Materials and methods: To characterize this possible association, a multicenter survey was made. Thus, we present a case series of five pediatric patients with 22q11.2 deletion syndrome or DiGeorge-like syndrome who were occasionally found with confirmed or highly suspected neoplasms of the thyroid gland during their follow-up. In three cases, malignancies were histologically confirmed, but their outcome was good due to an early recognition of suspicious nodules and precocious surgery. Conclusions: This study underlines for clinicians the higher risk of neoplasms in the head and neck district for patients affected by these syndromes. It also emphasizes the importance of a prolonged clinical and ultrasound follow-up for patients with this clinical and immunological phenotype.

Four-Component Recombinant Protein-Based Vaccine Effectiveness Against Serogroup B Meningococcal Disease in Italy.

Importance: Population-based data on the 4-component recombinant protein-based (4CMenB) vaccine effectiveness and reduction in incidence rate ratios (IRRs) are continuously needed to assess vaccine performance in the prevention of serogroup B invasive meningococcal disease (IMD). Objective: To assess the effectiveness and reduction in IRRs associated with the 4CMenB vaccine in the pediatric population in 6 regions in Italy. Design, Setting, and Participants: This retrospective cohort screening study and case-control study included data from children aged younger than 6 years in 6 highly populated Italian regions from January 1, 2006, to January 1, 2020. Participants included children younger than 6 years diagnosed with serogroup B IMD without predisposing factors. Data were collected from regional surveillance and vaccination registries and were analyzed from September 2021 to January 2022. Exposures: Routine 4CMenB vaccination, per regional vaccination programs. Main Outcomes and Measures: The main outcome was the effectiveness of the 4CMenB vaccine in the prevention of serogroup B IMD in the population of children aged younger than 6 years in 6 Italian regions. The percentages of vaccine effectiveness (VE) were obtained through the concomitant use of a screening method and a case-control study. Secondary outcomes were the comparison of effectiveness results obtained using the 2 different computational methods, the description of serogroup B IMD incidence rates, and reduction in IRRs before and after 4CMenB introduction, as a proxy for vaccine impact. Results: The cohort screening study included a resident population of 587 561 children younger than 6 years in 3 regions with similar surveillance protocols, and the matched-case controls study assessed a resident population of 1 080 620 children younger than 6 years in 6 regions. Analyses found that 4CMenB VE in fully immunized children was 94.9% (95% CI, 83.1%-98.4%) using the screening method and 91.7% (95% CI, 24.4%-98.6%) using the case-control method. Overall reduction in IRR was 50%, reaching 70% in regions with early-start vaccination schedules. The case-control method involving 6 highly-populated Italian regions included 26 cases and 52 controls and found an estimated VE of 92.4% (95% CI, 67.6%-97.9%) in children old enough for the first vaccine dose and 95.6% (95% CI, 71.7%-99.1%) in fully immunized children. VE was more than 90% for partially immunized children. Even in regions where the first dose was administered at age 2 months, almost 20% of unvaccinated cases were among infants too young to receive the first 4CMenB dose. Conclusions and Relevance: This screening cohort study and matched case-controls study found high effectiveness of 4CMenB vaccination and greater reduction in IRR for early-start vaccination schedules in preventing invasive serogroup B meningococcal disease. The high proportion of children too young to be vaccinated among unvaccinated cases suggests that starting the vaccination even earlier may prevent more cases. Screening and case-control methods provided similar estimates of VE: either method may be used in different study settings, but concomitant use can provide more robust estimates.

Human Bocavirus in Childhood: A True Respiratory Pathogen or a "Passenger" Virus? A Comprehensive Review.

Recently, human bocavirus (HBoV) has appeared as an emerging pathogen, with an increasing number of cases reported worldwide. HBoV is mainly associated with upper and lower respiratory tract infections in adults and children. However, its role as a respiratory pathogen is still not fully understood. It has been reported both as a co-infectious agent (predominantly with respiratory syncytial virus, rhinovirus, parainfluenza viruses, and adenovirus), and as an isolated viral pathogen during respiratory tract infections. It has also been found in asymptomatic subjects. The authors review the available literature on the epidemiology of HBoV, the underlying risk factors associated with infection, the virus's transmission, and its pathogenicity as a single pathogen and in co-infections, as well as the current hypothesis about the host's immune response. An update on different HBoV detection methods is provided, including the use of quantitative single or multiplex molecular methods (screening panels) on nasopharyngeal swabs or respiratory secretions, tissue biopsies, serum tests, and metagenomic next-generations sequencing in serum and respiratory secretions. The clinical features of infection, mainly regarding the respiratory tract but also, though rarely, the gastrointestinal one, are extensively described. Furthermore, a specific focus is dedicated to severe HBoV infections requiring hospitalization, oxygen therapy, and/or intensive care in the pediatric age; rare fatal cases have also been reported. Data on tissue viral persistence, reactivation, and reinfection are evaluated. A comparison of the clinical characteristics of single infection and viral or bacterial co-infections with high or low HBoV rates is carried out to establish the real burden of HBoV disease in the pediatric population.

Immunogenicity and safety of a quadrivalent meningococcal tetanus toxoid-conjugate vaccine (MenACYW-TT): A review of the evidence and expert opinion.

INTRODUCTION: Serogroups A, B, C, W, X, and Y of Neisseria meningitidis are responsible for almost all cases of invasive meningococcal disease. In Italy, vaccination against serogroup B is recommended at 3-13 months, C at 13-15 months, and A, C, Y and W in adolescents (12-18 years). Four quadrivalent meningococcal conjugate vaccines are available. This review describes the available data on a quadrivalent meningococcal tetanus toxoid-conjugate vaccine (MenACYW-TT; MenQuadfi®; Sanofi). AREAS COVERED: We identified articles on quadrivalent meningococcal conjugate vaccines indexed on PubMed since 2000. Of the 524 studies identified, 10 human studies investigating the immunogenicity and safety of MenACYW-TT in toddlers, children aged 2-9 years, and individuals 10-55 or ≥56 years are described in detail. EXPERT OPINION: In Italy, pediatric and public health groups recommend amending the current vaccination schedule to include a booster dose between 6 and 9 years and quadrivalent vaccine in young adults (≥19 years), targeting waning protection after childhood vaccination and the age cohort with the highest carrier prevalence (adolescents and young adults). MenACYW-TT is a suitable meningococcal vaccine for current and pending recommendations based on high seroprotection rates and a low incidence of adverse events in these age groups. Moreover, it does not require reconstitution.

Dermal Substitutes and Skin Grafts in the Reconstruction of Post-Traumatic Total Scalp Avulsion: A Case Series.

Although scalp defects can vary in size and thickness, scalp avulsion represents a rare occurrence. This type of lesion may have different origins, but it is usually related to long hair being caught in agricultural machinery. The management of full-thickness scalp defects poses a challenge to the head and neck surgeon due to the possible involvement of neurovascular structures and scar retraction, which can affect the esthetic restoration of the area. Several algorithms for the choice of scalp reconstruction have been proposed in the literature and different techniques are available for extensive scalp defect reconstruction (local soft tissue flap, microvascular free flap, and skin graft combined with dermal substitutes), based upon the scalp defect type. Here we describe six cases of patients with total scalp avulsion, which required a combined reconstruction with a split-thickness skin graft (STSG) and Integra® matrix immediately after the trauma.

CD38high/HLA-DR+ CD8+ T cells as potential biomarker of hemophagocytic lymphohistiocytosis secondary to visceral Leishmania infection.

Leishmaniasis is a cause of infection associated with hemophagocytic lymphohistiocytosis (HLH). The measurement of the CD8+ CD38high/HLA-DR+ T cells in children presenting with acute onset of shock and multisystem organ failure represents an important parameter to distinguish HLH from sepsis or healthy control. CONCLUSION: We report a case series of 4 Italian children suffering from HLH secondary to visceral Leishmaniasis in which the lymphocyte subset assay suggests a potential role of CD38high/HLA-DR+ CD8+ T cells as HLH diagnostic biomarkers. WHAT IS KNOWN: • Visceral Leishmaniasis is a well-known cause of infection associated with hemophagocytic lymphohistiocytosis (HLH). • The measurement of the CD8+ CD38high/HLA-DR+ T cells in children presenting with acute onset of shock and multisystem organ failure represents an important diagnostically useful parameter to readily distinguish HLH from sepsis or healthy controls. WHAT IS NEW: • We report a case series of 4 Italian children suffering from HLH secondary to visceral Leishmaniasis in which the lymphocyte subset assay suggests a potential role of CD38high/HLA-DR+ CD8+ T cells as HLH diagnostic biomarker. • The flow cytometry assay, performed at the disease onset before starting treatment, revealed a mean percentage value of CD38 cells of 36.95% among CD8+ T cells.

Deciphering variable resistance to novel carbapenem-based ß-lactamase inhibitor combinations in a multi-clonal outbreak caused by Klebsiella pneumoniae carbapenemase (KPC)-producing Klebsiella pneumoniae resistant to ceftazidime/avibactam.

OBJECTIVES: Carbapenemase-producing Enterobacterales represent a major cause of difficult-to-treat infections world-wide. Novel ß-lactam/ß-lactamase inhibitor combinations, including ceftazidime/avibactam (CZA), meropenem/vaborbactam (MVB), and imipenem/relebactam (IMR), represented a break-through in the treatment of some carbapenemase-producing Enterobacterales infections. However, acquired resistance to these agents has been reported in Klebsiella pneumoniae carbapenemase (KPC)-producing Enterobacterales. Herein, we reported an outbreak caused by CZA-resistant, KPC-producing Klebsiella pneumoniae (KPC-Kp), which was also variably resistant to carbapenem-based ß-lactam/ß-lactamase inhibitor combinations. METHODS: Bacterial isolates were subjected to antimicrobial susceptibility testing, whole-genome sequencing, determination of blaKPC gene dosage, and analysis of carbapenemase activity. RESULTS: Overall, 15 KPC-Kp, nine CZA-resistant (CZAR), and six CZA-susceptible isolates were collected from an outbreak involving six patients in a neurorehabilitation facility. Of the nine CZAR isolates, seven were also resistant to MVB and one was also resistant to IMR. Whole-genome sequencing revealed that the outbreak was multi-clonal, with CZAR KPC-Kp belonging to the ST101, ST1519, and two ST512 sub-lineages, which were involved in two independent transmission clusters. Resistance to CZA was primarily mediated by overproduction of KPC-3 associated with increased gene dosage, a mechanism accounting for cross-resistance to MVB in most cases, and to IMR in a single KPC-Kp isolate; multiple OmpK36 aletarions were also detected. Mutated KPC (KPC-53) was detected in a single case. Positivity for CZAR KPC-Kp was inconstantly associated with previous CZA exposure. CONCLUSIONS: In this multi-clonal outbreak of KPC-Kp, the overproduction of KPC-3 was the leading mechanism of cross-resistance to CZA and MVB, whereas resistance to IMR appeared less affected. The emergence and dissemination of similar resistance mechanisms may have relevant clinical and diagnostic implications, and their surveillance is warranted.