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Background:Although most cases of SARS-CoV-2 infection in pediatric population are asymptomatic or mild, severe cases may occur in a small percentage. Unlike other respiratory infections, children usually develop it from infected adults. Percentage of seroconversión and outcome of antibodies after infection anti-SAR-CoV-2 in children are still poorly understood and may be different from adults. The first aim was to describe clinical and epidemiological characteristics of pediatric patients diagnosed of SARS-CoV-2 infection in the second epidemic wave in two tertiary hospitals in Madrid, Spain and to determine the proportion of seronegative by comparing 3 serological techniques. As secondary aim it was proposed to determine the proportion of seronegative by comparing 3 serological techniques, seroconversion associated variables and the way of infection among the family members. Methods:Multicenter prospective observational study in two university hospitals of the Community of Madrid, between September and November 2020, of COVID-19 infection confirmed by PCR in the Emergency Department. A retrospective data collection was performed at 4-8 weeks after diagnosis on an outpatient basis, using a clinical-epidemiological questionnaire. At this time blood samples were collected to analyse the humoral response by 3 different serological assays.The quantitative variables are expressed as medians (interquartile range (IQR) 25-75).Univariate analysis of possible factors associated with seropositivity absence was performed.Results: One hundred and eleven patients (58 girls) were included with a median days of 37 (IQR: 34-44) between diagnosis and serologic test performed.Median age was 88 (IQR: 24-149) months. Parents were from abroad in 62 cases (50% from South and Central America).Ninety eight children were symptomatic, 17 children were diagnosed by epidemiological screening, 4 of whom subsequently developed symptoms.Eight of them needing admission with a median length of stay 2 days (IQR: 2-4), none of them in PICU.Underlying conditions were found in 33 patients, mainly recurrent bronchitis.Most frequent symptoms (70%) were low-grade fever (37-38ºC) or fever (≥ 38ºC), rhinorrhea 44%, cough 31.5%, headache 29.7%, weakness 27%, diarrhea 19.8%, abdominal pain and vomiting 26%, anosmia 16.2% (median 10 days; IQR: 6-30). Infection was interpreted as a secondary case in 56 patients, being a relative the index case in 96.4%. Seronegativity was observed in 19 patients in any of the 3 serological techniques (17.1%; 95% CI: 10.6-25.4), this proportion was higher among children aged 2-to 10-year-old age (16 of 45; 35%, p Conclusions: Our results confirm the mild clinical picture in children during the second epidemic wave, and that in most cases, children are not the index case in the family. Likewise, in children the proportion in whom seroconversion is not detected is high, and seems higher than that reported in adults. In our series, an association of seronegativity was seen in the 2 to 10 year-old age group and when there was no documentation of COVID-19 in any household contact.

Infections caused by ceftolozane-tazobactam and ceftazidime-avibactam-resistant P. aeruginosa infections are an emerging concern. We aimed to analyze the underlying ceftolozane-tazobactam and ceftazidime-avibactam resistance mechanisms in all multidrug-resistant or extensively drug-resistant (MDR/XDR) P. aeruginosa isolates recovered during 1 year (2020) from patients with a documented P. aeruginosa infection. Fifteen isolates showing ceftolozane-tazobactam and ceftazidime-avibactam resistance were evaluated. Clinical conditions, previous positive cultures, and β-lactams received in the previous month were reviewed for each patient. MICs were determined by broth microdilution. Multilocus sequence types (MLSTs) and resistance mechanisms were determined using short- and long-read whole-genome sequencing (WGS). The impact of Pseudomonas-derived cephalosporinases (PDCs) on β-lactam resistance was demonstrated by cloning into an ampC-deficient PAO1 derivative (PAOΔC) and construction of 3D models. Genetic support of acquired β-lactamases was determined in silico from high-quality hybrid assemblies. In most cases, the isolates were recovered after treatment with ceftolozane-tazobactam or ceftazidime-avibactam. Seven isolates from different sequence types (STs) owed their β-lactam resistance to chromosomal mutations and all displayed specific substitutions in PDC: Phe121Leu and Gly222Ser, Pro154Leu, Ala201Thr, Gly214Arg, ΔGly203-Glu219, and Glu219Lys. In the other eight isolates, the ST175 clone was overrepresented (6 isolates) and associated with IMP-28 and IMP-13, whereas two ST1284 isolates produced VIM-2. The cloned PDCs conferred enhanced cephalosporin resistance. The 3D PDC models revealed rearrangements affecting residues involved in cephalosporin hydrolysis. Carbapenemases were chromosomal (VIM-2) or plasmid-borne (IMP-28, IMP-13) and associated with class-1 integrons located in Tn402-like transposition modules. Our findings highlighted that cephalosporin/β-lactamase inhibitors are potential selectors of MDR/XDR P. aeruginosa strains producing PDC variants or metallo-β-lactamases. Judicious use of these agents is encouraged.

Data regarding humoral and cellular response against SARS-CoV-2 in children are scarce. We analysed seroconversion rate, decrease of anti-RBD IgG antibodies over time and T-cell response in paediatric patients who suffered COVID-19.Longitudinal study of paediatric patients COVID-19 diagnosed by positive molecular assay in nasopharyngeal swabs. Blood samples were drawn 1-2 months and 6-7 months after acute infection. Anti-RBD IgG were determined using the Alinity® SARS-CoV-2 IgG II Quant assay (Abbott). Cellular immune response was analysed by T-SPOT® SARS-CoV-2 assay kit (Oxford Immunotec Ltd.).27/39 (69,2%) patients seroconverted. Despite a significant decrease in antibody levels over time (p 0,01), no children seroreverted between first and second visits. Only 6/16 (37,2%) children under 6 years-old were seropositive compared to 21/23 (91,3%) over 6 years-old (p 0,01). Highest antibody levels were found in seropositive younger children (p = 0,036). Thirteen (33,3%) children showed T-cell response. Among participants showing humoral response, no cellular response was detected in 14 (51,9%).Anti-RBD IgG antibodies persistence at 6-7-months after SARS-CoV-2 infection was observed. A different IgG response was found depending on age. As measured by T-SPOT, most patients did not display cellular response 6-7 months after infection.