AUTHOR=Kifer Domagoj , Bugada Dario , Villar-Garcia Judit , Gudelj Ivan , Menni Cristina , Sudre Carole , Vučković Frano , Ugrina Ivo , Lorini Luca F. , Posso Margarita , Bettinelli Silvia , Ughi Nicola , Maloberti Alessandro , Epis Oscar , Giannattasio Cristina , Rossetti Claudio , Kalogjera Livije , Peršec Jasminka , Ollivere Luke , Ollivere Benjamin J. , Yan Huadong , Cai Ting , Aithal Guruprasad P. , Steves Claire J. , Kantele Anu , Kajova Mikael , Vapalahti Olli , Sajantila Antti , Wojtowicz Rafal , Wierzba Waldemar , Krol Zbigniew , Zaczynski Artur , Zycinska Katarina , Postula Marek , Lukšić Ivica , Čivljak Rok , Markotić Alemka , Brachmann Johannes , Markl Andreas , Mahnkopf Christian , Murray Benjamin , Ourselin Sebastien , Valdes Ana M. , Horcajada Juan P. , Castells Xavier , Pascual Julio , Allegri Massimo , Primorac Dragan , Spector Tim D. , Barrios Clara , Lauc Gordan 

TITLE=Effects of Environmental Factors on Severity and Mortality of COVID-19

JOURNAL=Frontiers in Medicine

VOLUME=7

YEAR=2021

URL=https://www.frontiersin.org/journals/medicine/articles/10.3389/fmed.2020.607786

DOI=10.3389/fmed.2020.607786

ISSN=2296-858X

ABSTRACT=<p><bold>Background:</bold> Most respiratory viruses show pronounced seasonality, but for SARS-CoV-2, this still needs to be documented.</p><p><bold>Methods:</bold> We examined the disease progression of COVID-19 in 6,914 patients admitted to hospitals in Europe and China. In addition, we evaluated progress of disease symptoms in 37,187 individuals reporting symptoms into the COVID Symptom Study application.</p><p><bold>Findings:</bold> Meta-analysis of the mortality risk in seven European hospitals estimated odds ratios per 1-day increase in the admission date to be 0.981 (0.973–0.988, <italic>p</italic> &lt; 0.001) and per increase in ambient temperature of 1°C to be 0.854 (0.773–0.944, <italic>p</italic> = 0.007). Statistically significant decreases of comparable magnitude in median hospital stay, probability of transfer to the intensive care unit, and need for mechanical ventilation were also observed in most, but not all hospitals. The analysis of individually reported symptoms of 37,187 individuals in the UK also showed the decrease in symptom duration and disease severity with time.</p><p><bold>Interpretation:</bold> Severity of COVID-19 in Europe decreased significantly between March and May and the seasonality of COVID-19 is the most likely explanation.</p>