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. 2021 Jan 20:7:607786.
doi: 10.3389/fmed.2020.607786. eCollection 2020.

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

Domagoj Kifer  1 , Dario Bugada  2 , Judit Villar-Garcia  3 , Ivan Gudelj  4 , Cristina Menni  5 , Carole Sudre  5 , Frano Vučković  4 , Ivo Ugrina  6 , Luca F Lorini  2 , Margarita Posso  3 , Silvia Bettinelli  2 , Nicola Ughi  7 , Alessandro Maloberti  7   8 , Oscar Epis  7 , Cristina Giannattasio  7   8 , Claudio Rossetti  7 , Livije Kalogjera  9 , Jasminka Peršec  10   11 , Luke Ollivere  12 , Benjamin J Ollivere  12 , Huadong Yan  13   14 , Ting Cai  13 , Guruprasad P Aithal  12 , Claire J Steves  5 , Anu Kantele  15 , Mikael Kajova  15 , Olli Vapalahti  16   17 , Antti Sajantila  18   19 , Rafal Wojtowicz  20 , Waldemar Wierzba  20 , Zbigniew Krol  20 , Artur Zaczynski  20 , Katarina Zycinska  20   21 , Marek Postula  22 , Ivica Lukšić  23 , Rok Čivljak  24   25   26 , Alemka Markotić  24 , Johannes Brachmann  27   28 , Andreas Markl  27 , Christian Mahnkopf  27 , Benjamin Murray  29 , Sebastien Ourselin  29 , Ana M Valdes  12 , Juan P Horcajada  3 , Xavier Castells  3 , Julio Pascual  3 , Massimo Allegri  30 , Dragan Primorac  27   28   31   32   33   34 , Tim D Spector  5 , Clara Barrios  3 , Gordan Lauc  1   4
Affiliations

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

Domagoj Kifer et al. Front Med (Lausanne). .

Abstract

Background: Most respiratory viruses show pronounced seasonality, but for SARS-CoV-2, this still needs to be documented. Methods: 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. Findings: 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, p < 0.001) and per increase in ambient temperature of 1°C to be 0.854 (0.773-0.944, p = 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. Interpretation: Severity of COVID-19 in Europe decreased significantly between March and May and the seasonality of COVID-19 is the most likely explanation.

Keywords: COVID-19; humidity; mortality; mucins; seasonality.

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Conflict of interest statement

The authors declare that this study received funding from Zoe Global Ltd. The funder was not involved in the study design, collection, analysis, interpretation of data, the writing of this article or the decision to submit it for publication.

Figures

Figure 1
Figure 1
Mortality in people admitted in hospitals with COVID-19. (A) Hospitalization outcome (death/discharge) depending on the admission date (grouped in 2-week intervals) since the beginning of the pandemic. (B) Meta-analysis of the effects of admission date on mortality (presented as odds ratios per 1-day increase in admission date). In Helsinki, there were only two deaths, and in Zhejiang hospitals, four deaths, so they were not included in the meta-analysis. OR, odds ratio; CI, confidence interval.
Figure 2
Figure 2
Meta-analysis of the effects of temperature on mortality (presented as odds ratios per 1°C increase in average daily temperature during hospitalization). In Helsinki, there were only two deaths, and in Zhejiang hospitals, four deaths, so they were not included in the meta-analysis. OR, odds ratio; CI, confidence interval.
Figure 3
Figure 3
Data from 37,187 individuals/suspected COVID positives (I+) recording symptoms in the COVID Symptom Study application in the United Kingdom suggest that both severity (measured as weighted sum of symptoms accounting for difference at disease peak between those reporting hospital visit and those who do not) and duration of disease symptoms slightly decrease in the United Kingdom (median values and interquartile ranges are shown). Imputed status defined as per the application of the predictive model described by Menni et al. (12) was chosen over definite PCR diagnostic in order to avoid confounding factor of test access policy changes.
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