Lower respiratory tract infections (LRTIs) are one of the most common reasons for consultation in Primary Care centres. Differentiating between viral and bacterial aetiologies can be challenging, leading to inappropriate antibiotic prescribing. Lung ultrasound (LUS), an imaging test that gained particular relevance since the beginning of the SARS-CoV-2 pandemic, offers several advantages over the classic chest X-ray in detecting and monitoring LRTIs, especially when pleural involvement exists.

This study aims to correlate LUS findings with capillary blood C-Reactive Protein (CRP) values in patients with LRTIs, evaluating LUS as a diagnostic tool and its impact on therapeutic decisions. The descriptive observational study, conducted from January 2024 to December 2026 in Lleida, will include LRTI patients attending Primary Care centres. By validating LUS as a rapid and non-invasive diagnostic tool, unnecessary antibiotic prescriptions can be reduced, promoting LUS as a complementary test in Primary Care consultations. This will facilitate appropriate diagnosis and treatment decisions for patients with LRTIs, enhancing the overall management of respiratory infections.

Inclusion Criteria:

• Age ≥ 18 years old
• Clinical suspicion of LRTI defined as acute illness lasting less than 21 days, with cough as the main symptom, accompanied by at least one other lower respiratory symptom (such as sputum production, dyspnoea, difficult breathing, or chest pain) without any other explanation for the clinical picture.
• Ability to read, understand and willingness to give written consent to participate in the study.

Exclusion Criteria:

• Patients who have been treated with antibiotics during the last 14 days up to inclusion.
• Patients with hemodynamic instability or that need emergency medical care due to the current clinical condition.
• Previous diagnosis of lung or pleural cancer.
• Thoracic surgery within the past 60 days.
• Lung interstitial diseases.
• Patients who refuse to participate in the study

Patients with lower respiratory tract infections attending Primary Care centres in Lleida.