1. Background and study aims Pneumonia is the leading infectious cause of death in children worldwide. Although the diagnosis is clinical, a chest radiograph (CXR) is often necessary to clarify it, exposing the patient to radiation. Ultrasound has been increasingly used in the evaluation of the lung parenchyma without exposing patients to radiation. The pocket-size Point-of-Care Ultrasound (POCUS) can be used at the patient's bedside proving comfort and saving time. Evidence suggests that ultrasound can detect CAP (community-acquired pneumonia) in children with similar accuracy and reliability as CXR. However, few studies evaluated the ability to distinguish the aetiology of pneumonia and none used a pocket-size POCUS device. This study aims to assess, for the first time, the diagnostic accuracy of a pocket-size POCUS device for the etiological diagnosis of CAP vs. CXR, in paediatric ages. Secondarily, the investigators intend to evaluate the correlation between CXR image vs. ultrasound, the correlation between clinical progression and ultrasound images, and the diagnostic accuracy to detect complications.

2. Who can participate:

   The investigators will include, consecutively, all children aged >12 months and <18 years hospitalized to the Paediatric Department with the diagnosis of CAP on admission. The investigators will exclude children hospitalized with nosocomial pneumonia, with cystic fibrosis diagnosis or on long-term domiciliary ventilation.

3. What does the study involve:

   The diagnostic accuracy between POCUS and CXR in differentiating the type of pneumonia will be assessed. All participants will perform a POCUS at admission, daily during hospitalization, 15 days and 1 month after discharge. All children will also undergo a CXR upon admission and whenever necessary.

4. What are the possible benefits and risks of participating:

   Children will have a more frequent and serial assessment of CAP, which does not involve risks.

5. Where is the study run from:

   The study if from Centro Materno Infantil do Norte - Centro Hospitalar Universitário de Santo António, a tertiary paediatric referral centre.

6. When is the study starting and how long is it expected to run for:

The recruitment period is expected to start in January/2024 and end in January 2025.

The investigators will perform a prospective diagnostic cohort study in a tertiary paediatric referral centre to study the diagnostic accuracy of a pocket-size Point-of-Care Ultrasound (POCUS) device vs. chest radiograph (CXR) for the etiological diagnosis of CAP, in paediatric age. During 1 year, all children aged >12 months and <18 years admitted to the Paediatric Department with the diagnosis of CAP on admission will be included. At least 76 participants will be required. Two investigators will perform, independently, a POCUS at admission, daily during hospitalization, 15 days and 1 month after discharge. All children will also undergo a CXR upon admission and whenever necessary. A third investigator will classify the CXR independently. It will be used the General Electrics Vscan AirTM®, with Bluetooth connection to smartphone/tablet. It will be collected the systematized description of POCUS and CXR, sociodemographic, clinical and therapeutic variables. Statistical analysis will be performed using SPSS® version 28.

This study won a competitive grant from MSD Portugal. The amount will be applied exclusively in the systematization and standardization of the POCUS technique with the guidance of an external consultant, in the statistical analysis, in the dissemination of results through participation in a national and international congress and in the creation of a task-force for the national implementation of this technique in paediatric services. The design, implementation, analysis, and dissemination of this stury will be independent from MSD Portugal and from the entire responsibility of the authors.

Inclusion Criteria:

• Age >12 months and <18 years
• Hospitalization in the Paediatric Department
• CAP diagnosis on admission (based on the physician's clinical judgment, namely through clinical, analytical and/or CXR criteria)

Exclusion Criteria:

• Nosocomial pneumonia
• Cystic fibrosis diagnosis
• Long-term use of domiciliary ventilation.