The purpose of this observational study is to identify the risk factors that make bronchiolitis more severe in infants and toddlers. Bronchiolitis is a common viral lung infection that causes inflammation and airway obstruction, often leading to breathing difficulties and hospitalization in young children.

Researchers will observe approximately 65 children, aged 1 to 24 months, who are admitted to Assiut University Hospital for acute bronchiolitis. Because this is an observational study, participants will receive standard medical care, and no experimental treatments will be tested.

During the hospital stay, researchers will collect information through parent questionnaires and standard medical records. The research team will gather data on:

• Family, social, and environmental factors, such as infant feeding practices, premature birth, and exposure to passive smoking.
• The child's clinical symptoms and overall severity of illness upon arrival at the hospital.
• Routine test results and the types of supportive care the child needs, such as extra oxygen or feeding assistance.
• The total length of the hospital stay and whether the child requires intensive care (ICU) admission.

By identifying which factors are most closely linked to severe illness, the study aims to help doctors better predict the course of the disease early on, evaluate adherence to treatment guidelines, and ultimately reduce the health burden of bronchiolitis.

Acute bronchiolitis represents the most common lower respiratory tract infection in children under two years of age, imposing a substantial healthcare burden, particularly in low-resource settings. The severity of the disease hinges on a combination of host factors (such as prematurity, low birth weight, and lack of exclusive breastfeeding) and environmental exposures (including passive smoking, crowded living conditions, and low socioeconomic status). This prospective observational cohort study aims to identify and quantify these risk factors and determine their impact on clinical outcomes for patients admitted to Assiut University Hospital.

Upon hospital presentation and confirmation of eligibility, a structured questionnaire will be administered to the parents or guardians to collect comprehensive sociodemographic data, including parental education, occupation, and specific infant feeding practices. Concurrently, a pediatrician will conduct a standardized clinical assessment to evaluate the presence and severity of respiratory signs, such as tachypnea, retractions, accessory muscle use, nasal flaring, grunting, and baseline oxygen saturation levels.

Throughout the patient's hospital stay, the research team will document diagnostic investigation patterns to evaluate adherence to evidence-based guidelines. This includes tracking the utilization of routine blood analyses (Complete Blood Count, C-reactive protein, Arterial Blood Gas) and radiological evaluations (Chest X-ray), which are typically discouraged for routine use but may be utilized for suspected complications.

Furthermore, clinical management strategies will be closely monitored and recorded. The research team will track the escalation of oxygen therapy, ranging from low-flow nasal cannula to high-flow nasal cannula (HFNC) and continuous positive airway pressure (CPAP/BiPAP), as well as feeding support interventions, such as nasogastric tube feeding requirements. Data will be statistically analyzed to assess the prevalence of modifiable risk factors and correlate these variables with the overall length of stay, intensive care needs, mechanical ventilation requirements, and 30-day readmission rates.

Inclusion Criteria:

• Children aged 1-24 months presenting with acute bronchiolitis, defined per AAP 2014 criteria: preceding upper respiratory infection, wheezing, tachypnoea (>60 breaths/min <2 months, >50 <12 months, >40 >12 months), and signs of respiratory distress (nasal flaring, grunting, retractions).
• Confirmed clinical diagnosis by a pediatric pulmonologist.

Exclusion Criteria:

• Known congenital heart disease, chronic lung disease (e.g., bronchopulmonary dysplasia), immunodeficiency, or neuromuscular disorders.
• Recurrent wheezing suggesting asthma.
• Gestational age <32 weeks without recovery or birth weight <1500g without catch-up growth.
• Immunosuppression, recent (within 2 weeks) systemic steroids or antibiotics.

The study population consists of hospitalized children aged 1 to 24 months presenting with acute bronchiolitis at Assiut University Hospital. Patients are eligible if they have a clinical diagnosis confirmed by a pediatric pulmonologist according to the AAP 2014 criteria, presenting with a preceding upper respiratory infection, wheezing, tachypnea, and signs of respiratory distress. The population strictly excludes children with underlying comorbidities that might independently affect respiratory severity, including known congenital heart disease, chronic lung disease, immunodeficiencies, and neuromuscular disorders. Furthermore, patients with a history of recurrent wheezing, extreme prematurity (gestational age <32 weeks without recovery) or low birth weight (<1500g without catch-up growth), and those who have received systemic steroids or antibiotics within the past two weeks are excluded from the study cohort.