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Background: Haemolytic uremic syndrome (HUS) is a thrombotic microangiopathy characterized by haemolytic anaemia, thrombocytopenia, and acute kidney injury. It represents the most frequent cause of acute kidney failure in paediatric age. HUS includes acquired types, such as post-infectious forms, and inherited types. If not promptly recognized, HUS still has high mortality and morbidity, with disabling long-term sequelae. Methods: Children diagnosed with HUS hospitalized between January 2010 and July 2021 at Meyer Children’s Hospital were retrospectively studied. Results: We selected 33 patients (M:F = 15:18) with a median age of 40 months (range 12–180 months). Twenty-eight cases (84.8%) were classified as acquired HUS: Shiga-like toxin Escherichia coli-related-HUS (STEC-HUS) was diagnosed in 26 patients (78.8%), while other 2 patients had HUS secondary to Streptococcus pneumoniae infections (3%) and hematopoietic stem cell transplantation (3%), each one. Five cases (15.1%) were classified as hereditary HUS: 4 patients (12.1%) presented inherited complement disorders (atypical HUS); 1 patient (3%) was diagnosed with cobalamin C deficiency. Diarrhoea was the most rated symptom (72.7%), mainly in STEC-HUS forms. In hereditary HUS, kidney involvement manifestations prevailed. Hypertension was present in 54.5% of total cases. Hypocomplementemia was present in 48.5% of patients; 30.3% of patients needed hospitalization in paediatric intensive care unit (PICU). Early hypertension and hypocomplementemia resulted to be related to the disease severity for either acute phase or long-term outcome. Leucocytosis, thrombocytopenia, and worsen renal function indices were related to PICU hospitalization. Overall, the outcome was good: long-term complications persisted in 18.2% of cases; 1 patient developed kidney failure; no patient died. Conclusions: HUS is a multifactorial disease mostly affecting children between 3 and 5 years old. Hypertension, leucocytosis, hypocomplementemia, thrombocytopenia, increased renal function indices, and extrarenal manifestations are risk factors for the worst outcome.

Kounis Syndrome is defined as a hypersensitivity coronary disorder constituted by the association of an acute coronary syndrome with a hypersensitivity, allergic, anaphylactic or anaphylactoid reaction, in a pathophysiologic context involving mast-cells, platelets, eosinophils and various interacting inflammatory cells. Currently, Kounis Syndrome is established in the literature, as accompanied by a plethora of clinical case reports that further elucidate its aspects. To the best of our knowledge, a specific analysis regarding the pediatric data of Kounis Syndrome has never been performed. The aim of this review was to reveal all the pediatric Kounis Syndrome cases in the literature, in an attempt to define its clinical implications in children. Moreover, based on the data of this analysis, a new classification for Kounis Syndrome is proposed, focusing mainly in the presence or the absence of allergic myocardial infarction, as the central clinical feature for the stratification of the patients' clinical manifestations.