Benign acute childhood myositis (BACM) is a self-limited childhood illness, and viral infections mainly cause it. Clinical and laboratory alterations usually normalize rapidly; generally, the only medical intervention required is supportive (hydration and analgesic medication). The low awareness about BACM often led to delayed diagnosis and unneeded ancillary investigations. This study aims to better characterize the clinical and laboratory features of BACM to improve the diagnostic process and inpatient and outpatient management. We conducted a retrospective study selecting all children admitted to Meyer’s Children’s Hospital-IRCCS (Florence, Italy) with a diagnosis of BACM over the last 5 years, both those visited at Emergency Department (ED) and those admitted to the Pediatric Unit. Clinical, laboratory, and instrumental data were collected from electronic clinical records and analyzed. Overall, sixty-five patients were enrolled; 49 children were visited and discharged directly from ED, whereas 16 were admitted in the Pediatric or Neurologic Wards. The median age was 6.56 years (IQR 4.9–9.1). Male gender (66.1%) and Caucasian ethnicity (70%) were prevalent. Most patients were admitted during winter, and a second peak was found in autumn. All patients had bilateral calf pain, most of them (87.7%) associated with asthenia and refuse to walk (93.8%). Prodromal symptoms were fever (75.3%), cough (32.3%), coryza (26.1%), sore throat (26.1%), and vomiting (15.3%). The median value of CPK was 1827 U/L (IQR 915.5–2462) at peak. CPK median time to normalization was 7 days (IQR 7–8.5) from the nadir. Influenza B was the virus most frequently BACM associated, followed by Influenza A; a novel association with Sars-CoV-2 has been detected. Two patients had pathogenic variants at the Next Generation Sequencing myopathies panel. Conclusion: School-aged children admitted to the hospital with walking difficulty and myalgia, generally after an upper respiratory tract infection with a moderate CPK elevation, should remind at first of BACM. Rapid complaint resolution and biochemical markers normalization will prevent unnecessary tests and inappropriate therapies. What is Known:• BACM is a self-limited syndrome associated with acute infections. Influenza A and B viruses are the main etiological agents, but BACM may be related to many other microorganisms like Parainfluenza virus, Epstein-Barr virus, Cytomegalovirus, Human herpesvirus 6, Respiratory syncytial virus, Coxsackieviruses, Mycoplasma pneumoniae, Streptococcus pyogenes, Legionella, and Salmonella spp.• Clinical and laboratory alterations usually normalize rapidly; generally, the only medical intervention required is supportive (hydration, analgesic medication). Evolution in rhabdomyolysis and kidney damage is possible but rarely reported. What is New:• Sars-CoV-2 could be an emerging possible cause of BACM. During and after the Sars-CoV-2 outbreak, virus infection seasonality has changed, and so has BACM seasonality.• Screening tests for muscular and metabolic disorders are recommended in recurrent myositis and/or cases with marked CPK elevation (≥ 5000 U/L).

This study aimed to evaluate the type and severity of neurological involvement in children with SARS-CoV-2 infection or multisystem inflammatory syndrome in children (MIS-C) and compare these findings between the two groups. Children hospitalized with the diagnosis of COVID-19 or MIS-C at Meyer Children’s Hospital between February 2020 and June 2022 were retrospectively studied. One hundred twenty-two patients were enrolled, 95 in the COVID-19 group and 27 in the MIS-C group. In the COVID-19 group, impairment of consciousness was found in 67.4% of patients, headache in 18.9% and about 16.8% of patients experienced seizures. In this group, three patients were diagnosed with arterial ischemic stroke and one patient was diagnosed with Guillain-Barré syndrome (GBS). In the MIS-C group, about 70% of patients experienced consciousness impairment, about 20% behavioral changes, and another 20% mood deflection. Neurological symptoms and signs were highly heterogeneous and could be differentiated in COVID-19 and MIS-C. Consciousness impairment remained the most frequent manifestation in both groups, potentially underlying an encephalopathy. We also highlight the importance of considering psychiatric symptoms in children with COVID-19 and/or MIS-C. Most neurological manifestations were mild in our series; however, severe complications such as ischemic stroke and GBS are worthy of note.

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.

Nirsevimab, a long-acting monoclonal antibody against respiratory syncytial virus (RSV), was recently introduced to prevent infant RSV-related hospitalizations. Although efficacy has been demonstrated in clinical trials, real-world data on targeted immunization strategies remain limited. We aimed to evaluate the effectiveness of nirsevimab in preventing RSV-associated hospitalizations in infants under 12 months, within a seasonal program prioritizing infants born from April onwards. We conducted a prospective, multicenter, matched case-control study across seven Italian hospitals during the 2024-2025 RSV season. Infants hospitalized with PCR-confirmed RSV bronchiolitis were matched 1:2 by age and date of admission to controls hospitalized for non-respiratory causes. Data were collected via electronic medical records. Immunization effectiveness (IE) was estimated using conditional logistic regression adjusted for sex assigned at birth, gestational age, birth weight, and clinical risk factors. Two pre-specified stratified analyses and a sensitivity analysis using inverse probability of treatment weighting (IPTW) were performed. A total of 138 infants were included (46 cases, 92 controls). Adjusted IE was 89.5% (95% CI: 60.3-97.2%). Stratified analyses yielded similar results among infants born after April 1 (IE: 88.4%, 95% CI: 56.5-96.9%) and those without risk factors (IE: 88.1%, 95% CI: 45.7-97.4%). IPTW analysis confirmed protection (IE: 79.6%, 95% CI: 53.5-91.0%). This study provides real-world evidence supporting the effectiveness of nirsevimab in a targeted seasonal immunization framework. These findings may inform phased implementation strategies and RSV prophylaxis policies in varied healthcare settings.

Background: Pelvic acute hematogenous osteomyelitis (PAHO) is an uncommon pediatric infection often presenting with nonspecific symptoms, resulting in delayed diagnosis. Data on its clinical presentation, microbiology, management and outcomes remain limited. Methods: A retrospective single-center study included children diagnosed with pelvic AHO at Meyer Children’s Hospital IRCCS (Florence, Italy) between January 2016 and December 2025. Patients were stratified into isolated osteomyelitis and osteomyelitis with septic arthritis. Results: Thirty-seven children were included, representing 16% of all AHO cases during the study period. Median age was 8.9 years (interquartile range [IQR] 4.1–12.1); 70% were male. The ilium was most frequently involved. Sixteen patients (43.2%) had concomitant septic arthritis and were significantly older than those with isolated osteomyelitis ( P = 0.019). Isolated osteomyelitis was associated with longer time to diagnosis (median 8 days, IQR 6–14) versus septic arthritis (median 5 days, IQR 4–8.5; P = 0.025). Concomitant pyomyositis was identified in 67.5% of cases. A pathogen was isolated in 43.2% of patients, most commonly methicillin-susceptible Staphylococcus aureus . Median intravenous antibiotic duration was 17 days, total antibiotic duration 45 days. Treatment failure occurred in 16.2%, chronic complications in 5.4%. Conclusions: PAHO encompasses 2 distinct clinical phenotypes, isolated osteomyelitis and osteomyelitis with septic arthritis, differing in age at presentation, inflammatory response, and diagnostic delay. Magnetic resonance imaging is essential for defining disease extent, identifying associated pyomyositis, and guiding management.