This observational study will describe lung ultrasound (LUS) findings over time in hospitalized patients with moderate to severe Covid-19 lung disease. Our primary aim is to investigate if lung ultrasound can identify and/or predict patients requiring mechanical ventilation. Another aim is to describe LUS findings associated with clinical findings and patient condition.

Study patients with moderate to severe Covid-19 infection will be screened with lung ultrasound daily. Lung ultrasound will be assessed by LUS-score for acute respiratory distress syndrome (ARDS) (0-36 points, Bouhemad 2015). Findings of B-line artifacts and consolidations will be noted. In addition to LUS, clinical parameters from physical examination and laboratory tests will be collected. Participants wil be followed until either admission to intensive care unit (ICU) for mechanical ventilation or until clinical improvement. A group of patients with mild Covid-19 infection will be recruited and screened once as reference.

Apart from assessment with LUS, patients are managed according to routine care.

Inclusion Criteria:

• Covid-19 confirmed by positive polymerase chain reaction (PCR)
• oxygen by mask or nasal prongs ≥ 4 l/min or high flow nasal cannula (HFNC) with fraction of inspired oxygen (FiO2) ≥ 30%
• age between 18-80 years
• informed consent

Exclusion Criteria:

• patients subject to treatment-limitation "no ICU"
• history of heart failure
• history of lung disease e.g.: pneumonectomy, pulmonary fibrosis or other interstitial lung disease, pleurodesis
• history of kidney failure requiring dialysis
• any reason making lung ultrasound or daily follow up impossible
• opposition to participation in the study

Hospitalized adult patients with confirmed Covid-19 and oxygen therapy corresponding to stage 4-5 on the "Ordinal Scale for Clinical Improvement" of the World Health Organization.