The causative agent of COVID-19 is the SARS-CoV-2. The severe form of COVID-19 is most often contracted by elderly and in patients with comorbidities. The aim of the study was to analyse the viral load in patients with severe COVID-19. The aim was to investigate whether the viral load in the lower respiratory tract declines more slowly in elderly patients than in younger patients, whether the viral dynamics in the lower and upper respiratory tract are the same, and whether the genetic variant of SARS-CoV-2 influences the viral dynamics. A total of 404 nasopharyngeal swabs, 493 tracheal aspirates, 132 bronchoalveolar lavages and 19 sputum samples were collected from 100 patients treated for COVID-19 in the intensive care unit. Nucleic acid was isolated from the lower respiratory tract samples and real-time quantitative RT-PCR was performed to measure viral load. The results showed that the SARS-CoV-2 viral load in the upper and lower respiratory tract declined more slowly in patients older than 65 years. Also, viral dynamics was different in samples from the upper in comparison to samples from lower respiratory tract. The SARS- CoV-2 viral load dynamics was influenced also by virus genetic variant.
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