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Although the pulmonary compartment represents a relevant site for viral load analysis, limited data exploring the lower respiratory tract is available, and its association to clinical outcomes is relatively unknown. Using bronchoalveolar lavage (BAL) and serum samples, we quantified SARS-CoV-2 copy numbers in the pulmonary and systemic compartments of critically ill patients admitted to the intensive care unit of a COVID-19 referral hospital in Croatia during the second and third pandemic waves. Clinical data, including 30-day survival after ICU admission, were included. We found that elevated SARS-CoV-2 copy numbers in both BAL and serum samples were associated with fatal outcomes. Remarkably, the highest and earliest viral loads after initiation of mechanical ventilation support were increased in the non-survival group. Our results imply that viral loads in the lungs contribute to COVID-19 disease severity, while blood titers correlate with lung virus titers, albeit at a lower level. Moreover, they suggest that BAL SARS-CoV-2 copy number quantification at ICU admission may provide a predictive parameter of clinical COVID-19 outcomes.<\/jats:p>","DOI":"10.3390\/v14061292","type":"journal-article","created":{"date-parts":[[2022,6,15]],"date-time":"2022-06-15T01:39:54Z","timestamp":1655257194000},"page":"1292","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":14,"title":["SARS-CoV-2 Viral Load in the Pulmonary Compartment of Critically Ill COVID-19 Patients Correlates with Viral Serum Load and Fatal Outcomes"],"prefix":"10.3390","volume":"14","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-8586-3993","authenticated-orcid":false,"given":"Mario","family":"Ynga-Durand","sequence":"first","affiliation":[{"name":"Helmholtz Center for Infection Research, Department of Viral Immunology, 38124 Braunschweig, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4654-5423","authenticated-orcid":false,"given":"Henrike","family":"Maa\u00df","sequence":"additional","affiliation":[{"name":"Helmholtz Center for Infection Research, Department of Viral Immunology, 38124 Braunschweig, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Marko","family":"Milo\u0161evi\u0107","sequence":"additional","affiliation":[{"name":"Department of Anesthesiology, Reanimation, Intensive Care and Emergency Medicine, Faculty of Medicine, University of Rijeka, 51000 Rijeka, Croatia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2779-0359","authenticated-orcid":false,"given":"Fran","family":"Krstanovi\u0107","sequence":"additional","affiliation":[{"name":"Center for Proteomics, Faculty of Medicine, University of Rijeka, 51000 Rijeka, Croatia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0355-1572","authenticated-orcid":false,"given":"Marina","family":"Pribani\u0107 Mate\u0161i\u0107","sequence":"additional","affiliation":[{"name":"Center for Proteomics, Faculty of Medicine, University of Rijeka, 51000 Rijeka, Croatia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Stipan","family":"Jonji\u0107","sequence":"additional","affiliation":[{"name":"Center for Proteomics, Faculty of Medicine, University of Rijeka, 51000 Rijeka, Croatia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6573-852X","authenticated-orcid":false,"given":"Alen","family":"Proti\u0107","sequence":"additional","affiliation":[{"name":"Department of Anesthesiology, Reanimation, Intensive Care and Emergency Medicine, Faculty of Medicine, University of Rijeka, 51000 Rijeka, Croatia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8839-7839","authenticated-orcid":false,"given":"Ilija","family":"Brizi\u0107","sequence":"additional","affiliation":[{"name":"Center for Proteomics, Faculty of Medicine, University of Rijeka, 51000 Rijeka, Croatia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8393-4332","authenticated-orcid":false,"given":"Alan","family":"\u0160usti\u0107","sequence":"additional","affiliation":[{"name":"Department of Anesthesiology, Reanimation, Intensive Care and Emergency Medicine, Faculty of Medicine, University of Rijeka, 51000 Rijeka, Croatia"},{"name":"Department of Clinical Medical Science II, Faculty of Health Studies, University of Rijeka, 51000 Rijeka, Croatia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3978-778X","authenticated-orcid":false,"given":"Luka","family":"\u010ci\u010din-\u0160ain","sequence":"additional","affiliation":[{"name":"Helmholtz Center for Infection Research, Department of Viral Immunology, 38124 Braunschweig, Germany"},{"name":"German Centre for Infection Research (DZIF), Partner Site Hannover\/Braunschweig, 38124 Braunschweig, Germany"},{"name":"Centre for Individualised Infection Medicine (CiiM), A Joint Venture of Helmholtz Centre for Infection Research and Hannover Medical School, 30625 Hannover, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2022,6,14]]},"reference":[{"key":"ref_1","unstructured":"World Health Organization (2020). 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