Multisystem inflammatory syndrome associated with the SARS-CoV-2 pandemic has recently been described in children (MIS-C), partially overlapping with Kawasaki disease (KD). We hypothesized that (a) MIS-C and prepandemic KD cytokine profiles may be unique and justify the clinical differences observed, and (b) SARS-CoV-2–specific immune complexes (ICs) may explain the immunopathology of MIS-C. Seventy-four children were included: 14 with MIS-C, 9 patients positive for SARS-CoV-2 by PCR without MIS-C (COVID), 14 with prepandemic KD, and 37 healthy controls (HCs). Thirty-four circulating cytokines were quantified in pretreatment serum or plasma samples and the presence of circulating SARS-CoV-2 ICs was evaluated in MIS-C patients. Compared with HCs, the MIS-C and KD groups showed most cytokines to be significantly elevated, with IFN-γ–induced response markers (including IFN-γ, IL-18, and IP-10) and inflammatory monocyte activation markers (including MCP-1, IL-1α, and IL-1RA) being the main triggers of inflammation. In linear discriminant analysis, MIS-C and KD profiles overlapped; however, a subgroup of MIS-C patients (MIS-C^plus) differentiated from the remaining MIS-C patients in IFN-γ, IL-18, GM-CSF, RANTES, IP-10, IL-1α, and SDF-1 and incipient signs of macrophage activation syndrome. Circulating SARS-CoV-2 ICs were not detected in MIS-C patients. Our findings suggest a major role for IFN-γ in the pathogenesis of MIS-C, which may be relevant for therapeutic management.

Background: Bronchiolitis is the most common viral infection of the lower respiratory tract in infants under 2 years of age. The aim of this study was to analyze and compare the seasonal bronchiolitis peaks before and during the SARS-CoV-2 pandemic. Methods: Descriptive, prospective, and observational study. Patients with severe bronchiolitis admitted to the Pediatric Intensive Care Unit (PICU) of a referral tertiary hospital between September 2010 and June 2021 were included. Demographic data were collected. Viral laboratory-confirmation was carried out. Each season was analyzed and compared. The daily average temperature was collected. Results: 1116 patients were recruited, 58.2% of them males. The median age was 49 days. Respiratory syncytial virus (RSV) was isolated in 782 cases (70.1%). In April 2021, the first and only case of bronchiolitis caused by SARS-CoV-2 was identified. The pre- and post-pandemic periods were compared. There were statistically significant differences regarding: age, 47 vs. 73 days (p = 0.006), PICU and hospital length of stay (p = 0.024 and p = 0.001, respectively), and etiology (p = 0.031). The peak for bronchiolitis in 2020 was non-existent before week 52. A delayed peak was seen around week 26/2021. The mean temperature during the epidemic peak was 10ºC for the years of the last decade and is 23ºC for the present season. Conclusion: The COVID-19 pandemic outbreak has led to a clearly observable epidemiological change regarding acute bronchiolitis, which should be studied in detail. The influence of the environmental temperature does not seem to determine the viral circulation.

Introduction: Enterovirus A71 (EV-A71) is an emerging pathogen that causes a wide range of disorders including severe neurological manifestations. In the past 20 years, this virus has been associated with large outbreaks of hand, foot and mouth disease with neurological complications in the Asia-Pacific region, while in Europe mainly sporadic cases have been reported. In spring 2016, however, an EV-A71 outbreak associated with severe neurological cases was reported in Catalonia and spread further to other Spanish regions. Aim: Our objective was to investigate the epidemiology and clinical characteristics of the outbreak. Methods: We carried out a retrospective study which included 233 EV-A71-positive samples collected during 2016 from hospitalised patients. We analysed the clinical manifestations associated with EV-A71 infections and performed phylogenetic analyses of the 3’-VP1 and 3Dpol regions from all Spanish strains and a set of EV-A71 from other countries. Results: Most EV-A71 infections were reported in children (mean age: 2.6 years) and the highest incidence was between May and July 2016 (83%). Most isolates (218/233) were classified as subgenogroup C1 and 217 of them were grouped in one cluster phylogenetically related to a new recombinant variant strain associated with severe neurological diseases in Germany and France in 2015 and 2016. Moreover, we found a clear association of EV-A71-C1 infection with severe neurological disorders, brainstem encephalitis being the most commonly reported. Conclusion: An emerging recombinant variant of EV-A71-C1 was responsible for the large outbreak in 2016 in Spain that was associated with many severe neurological cases.

Hygiene behavior plays a relevant role in infectious disease transmission. The aim of this study was to evaluate non-pharmaceutical interventions (NPI) in preventing pediatric influenza infections. Laboratory confirmed influenza cases occurred during 2009–10 and 2010–11 seasons matched by age and date of consultation. NPI (frequency of hand washing, alcohol-based hand sanitizer use and hand washing after touching contaminated surfaces) during seven days prior to onset of symptoms were obtained from parents of cases and controls. Cases presented higher prevalence of underlying conditions such as pneumonia [OR = 3.23; 95 % CI: 1.38 – 7.58 p = 0.007], asthma [OR = 2.45; 95 % CI: 1.17 – 5.14 p = 0.02] and having more than 1 risk factor [OR = 1.67; 95 % CI: 0.99 – 2.82 p = 0.05]. Hand washing more than 5 times per day [aOR = 0.62; 95 % CI: 0.39 – 0.99 p = 0.04] was the only statistically significant protective factor. When considering two age groups (pre-school age 0–4 yrs and school age 5–17) yrs , only the school age group showed a negative association for influenza infection for both washing more than 5 times per day [aOR = 0.47; 95 % CI: 0.22 – 0.99 p = 0.04] and hand washing after touching contaminated surfaces [aOR = 0.19; 95 % CI: 0.04 – 0.86 p = 0.03]. Frequent hand washing should be recommended to prevent influenza infection in the community setting and in special in the school age group.

Background: Several clinical trials have shown that nirsevimab, an antibody targeting the respiratory syncytial virus (RSV), reduces RSV bronchiolitis requiring admission. In 2023–2024, Catalonia and Andorra adopted immunization strategies for children <6 months and those born during the epidemic season. This study evaluates the effectiveness of nirsevimab in preventing hospitalizations from RSV bronchiolitis.Methods: In the epidemic season of 2023–2024, a test‐negative case–control study was conducted in three hospitals from Catalonia and Andorra. Patients <12 months old admitted with bronchiolitis and tested for RSV using molecular microbiology tests were included.The effectiveness in preventing RSV bronchiolitis hospitalization and severe disease was estimated using multivariate models. Comparisons between immunized, non‐immunized, and non‐eligible patients were made in prospectively collected epidemiological, clinical, and microbiological variables.Results: Two hundred thirty‐four patients were included. RSV was detected in 141/234 (60.2%), being less common in the immunized group (37% vs 75%, p < .001). The rate of immunized patients among those eligible was 59.7%. The estimated effectiveness for RSV‐associated lower respiratory tract infection was 81.0% (95% confidence interval: 60.9–90.7), and for preventing severe disease (the need for NIV/CMV), 85.6% (41.7–96.4%). No significant differences by immunization status were observed in patients with RSV concerning viral coinfections, the need for NIV/CMV or length of hospital stay.Conclusions: This study provides real‐world evidence of the effectiveness of nirsevimab in preventing RSV‐lower respiratory tract infection hospitalization and severe disease in infants during their first RSV season following a systematic immunization program. Immunized patients did not exhibit a higher rate of viral coinfections nor differences in clinical severity once admitted.