Cohort 1: COVID-19 patients. Cohort 2: patients with lung diseases unrelated to COVID-19.

All the patients will be examined using confocal laser endomicroscopy during bronchoscopy with a special Alveoflex miniprobe during the hospitalisation period. Records will be done and analysed prospectively with the included software for the endomicroscopic system.

Using Alveoflex is a minimally invasive intervention.

Alveoflex uses 488nm laser, generating real time moving images with an optical area of 600μm at a video frame rate of 12 images per second and a focus depth of 50μm

pCLE images are assessed morphometrically. Such criteria as quantity of alveolar macrophages, quantity of floating intraalveolar substances etc. are measured using a 6-point score, where zero means the absence of the symptom and 5 means the maximal expressiveness. Thickness of interalveolar septum, diameter of microvessels and thickness of elastic fibers are measured using a special tool with the included software for the endomicroscopic system. Radiologic signs e.g. low-density areas and consolidation areas are assessed in Hounsfield Units. Other radiologic signs e.g. groundglass opacity, crazy paving patterns etc. are measured by a 5-point scale, where zero means the absence of the symptom and 4 means the maximal expressiveness. The morphological analysis of the lung tissue specimens (received as a result of autopsy/transbronchial biopsy) is made according to the structures in pCLE images for 20 fields of view.

pCLE images are assessed morphometrically. Such criteria as quantity of alveolar macrophages, quantity of floating intraalveolar substances etc. are measured using a 6-point score, where zero means the absence of the symptom and 5 means the maximal expressiveness. Thickness of interalveolar septum, diameter of microvessels and thickness of elastic fibers are measured using a special tool with the included software for the endomicroscopic system. Radiologic signs e.g. low-density areas and consolidation areas are assessed in Hounsfield Units. Other radiologic signs e.g. groundglass opacity, crazy paving patterns etc. are measured by a 5-point scale, where zero means the absence of the symptom and 4 means the maximal expressiveness. The morphological analysis of the lung tissue specimens (received as a result of autopsy/transbronchial biopsy) is made according to the structures in pCLE images for 20 fields of view.