Altitude conditions seem to determine the evolution of COVID-19 in Brazil: a signicance relationship with cases and deaths

Background COVID-19 is spreading rapidly in Brazil, a country of continental dimensions, but the incidence of the disease is showing to be very heterogeneous, affecting cities and regions differently. Thus, there is a gap regarding what factors would contribute to accentuate the differences in the incidence of COVID-19 among Brazilian cities. This work aimed to evaluate the effect of altitude on incidence of COVID-19 in Brazilian cities. We analysed the relative incidence, relative death rate of COVID-19, and air relative humidity in all 154 cities in Brazil with a population above 200 thousand inhabitants, located between 5 and 1,135 m in altitude. Pearson's correlation analysis was performed to compare a relationship between altitude with relative incidence (RI) and relative death rate (RDR) and between air relative humidity (RH). Altitudes were classied into three classes (low class, up to 97 m; middle class, 97 m to 795 m; and upper class, 795 m to 1,135 m) for the RI, RDR and RH variables. To compare the three classes of altitude, analysis of variance (ANOVA) and Tukey test were used to compare media (p < 0.05). Our epidemiological analysis found that the IR, RDR and RH were higher in cities located in low (0 to 97 m a.s.l) compared to medium (98 to 790 m a.s.l) and high (791 to 1135 m a.s.l) cities altitudes. Furthermore, it has been shown that there is a negative correlation between the incidence of COVID-19 with altitude and a positive correlation with air relative humidity in the cities analysed. Thus, establish


Introduction
In December 2019, a new coronavirus was identi ed -initially called 2019-nCoV and later renamed SARS-CoV-2 -in Hubei province, People's Republic of China [1]. The pathogen causes coronavirus-19 disease (COVID- 19), which spread rapidly, reaching the pandemic level on March 11, 2020 [2]. The incidence of cases and deaths caused by COVID-19 in the world increased at different rates from the rst cases. In Brazil, a country of continental dimensions, the spread of the disease is very heterogeneous, affecting cities and regions differently.
Efforts to minimize its spread are announced every minute in the media. Also, thousands of searches worldwide are focused on the various nuances of COVID- 19. However, studies that relate to the incidence of the disease to environmental factors are incipient, especially in countries like Brazil, which stands out for its great socioeconomic and environmental diversity [2]. As the behaviour of COVID-19 concerning climatic attributes is still poorly understood, investigating the in uence of altitude and environmental characteristics of cities on the incidence and deaths caused by COVID-19 can generate results that contribute to the development of public policies that minimize the spread of the disease. Table 1 Cities and regions of Brazil, altitude, population, relative incidence (RI), relative death rate (RDR), air relative humidity (RH). Data from the rst case, an The altitude varies between 5 and 1,135 m a.s.l., and the cities located at higher altitudes are in the central-west region, followed by the southeast and south regions. The northern region has the lowest altitude gradient, and all cities are below 180 m a.s.l. (Table 1).
On May 17, 2020, the RI varied between 4.74 (Rio Grande) and 593.78 (Recife) ( Table 1) and was higher in the north, followed by the northeast, southeast, central-west and, south (Table 2). On June 01, 2020, the RI varied between 12.10 (Sete Lagoas) and 1,063.49 (Sobral) ( Table 1) and was higher in the north, followed by the northeast, southeast, central-west and, south (Table 2). On June 16, 2020, the RI changed between 18.78 (Sete Lagoas) and 2,998.95 (Parauapebas) ( Table 1) and was also higher in the north, followed by the northeast, southeast, central-west, and south (Table 2). On July 01, 2020, the RI changed between 64.98 (Montes Claros) and 4,758.18 (Parauapebas) ( Table 1) and was higher in the north, followed by the northeast, central-west, southeast, and south (Table 2). respectively. The largest increase in RI was observed in the central-west region and the smallest in the northeast region (Table 2), and the rate of RI growth Page 9/13 decelerated in all regions, except in the southern region (Fig. 2).
Between May 17 and June 01, between June 02 and June 16, and between June 17 and July 01, the RDR increased respectively 78.4%, 45.5% and 34,6% in Brazil. The largest increase in RDR was observed in the central-west region and the smallest in the north region (Table 2), and the rate of RDR growth decelerated in all regions, except in the southern region (Fig. 2).
Between March 01 and May 17, 2020, the average air relative humidity (RH) data of 63 cities were analysed, which varied between 52 and 89.4% (Table 1) with an RH average of 74% (  ; p < 0.001) was highly signi cant. The means of RI, RDR, and RH were compared using the Tukey test, which showed that the incidence is higher at low altitudes in the four analysed periods (Fig. 3).
The rst con rmed case in Brazil occurred on February 26 of 2020 in the city of São Paulo, and until April 8 of 2020, all cities in Brazil with a population of up to 200 thousand inhabitants con rmed at least one case of COVID-19 (Table 1). There were no signi cant differences between cities concerning the period of accelerated dissemination. The r values of Pearson's correlation between altitude and RI and RDR and the F values of ANOVA for all dependent variables increased from the rst to the second analysed period. Would, then, the altitude and the air relative humidity have contributed to accelerate the spread of the virus in Brazil?

Discussion
Our epidemiological analysis of the COVID-19 pandemic in Brazil indicates a direct association between the incidence of COVID-19 with altitude and RH in Brazilian cities with a population above 200 thousand inhabitants. The highest RI and RDR in cities with lower altitudes may be related to environmental factors, which in uence the spread of the virus and the physiology of human beings.
Climatic factors can be determinant for transmission by some viruses [8]. Studies have shown that transmission of the in uenza virus is more favourable in tropical and subtropical countries than in countries with temperate climates [8]. However, it is necessary to consider comprehensive biophysical assessments of altitude, humidity, UV radiation in the maintenance and transmission of SARS-CoV-2. [9,10]. Recently studies have been published about temperature and UV index, and that heating, and UV irradiation can eliminate the viral infectivity [9,10]. These ndings could help to understand the relationship of COVID-19 cases in different cities Brazil due to altitude.

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In contrast to what other studies report regarding the greater spread of the in uenza virus in environments with lower air relative humidity [11], our data show that COVID-19 RI is higher in cities where RH is highest. These results are in line with those obtained by C Arias-Reyes, N Zubieta-DeUrioste, L Poma-Machicao, F Aliaga-Raudan, F Carvajal-Rodriguez, M Dutschmann, E Schneider-Gasser, G Zubieta-Calleja and J Soliz [3], which lists air dryness as one of the factors that control the spread of the virus at high altitudes. In working with climatic data from 5 large Brazilian cities (Manaus, Fortaleza, Brasília, Rio de Janeiro, and São Paulo), [12] showed that moderate relative air humidity (averages between 77.7 and 81.6%) favor the spread of this disease. In the present study, 5 cities with the highest RI, in the four periods analyzed, had an average RH between 79.3 and 84.8%, values similar to those found by A Auler, F Cássaro, V da Silva and L Pires [12].
Another point that must be considered is that the higher altitude in itself favors a higher incidence of ultraviolet (UV) radiation, especially in the UVA and UVB spectra, which can produce a bactericidal effect due to changes in the molecular chains of DNA and RNA. Thus, as a hypothesis, UV radiation would shorten the virus half-life, thereby reducing the virus's ability to survive in Brazilian cities located at higher altitudes and, consequently, the survival of the COVID-19 virus. Besides, considering that vitamin D production is dependent on exposure to UV radiation and that vitamin D levels positively modulate the immune system [13], the hypothesis of higher immune defense against SARS-CoV-2 is plausible in cities with higher altitude. Future studies should investigate this hypothesis.
The lower air density and greater distance between molecules in Brazilian cities located at higher altitudes could also reduce the inoculation of airborne viruses compared to sea level. C Arias-Reyes, N Zubieta-DeUrioste, L Poma-Machicao, F Aliaga-Raudan, F Carvajal-Rodriguez, M Dutschmann, E Schneider-Gasser, G Zubieta-Calleja and J Soliz [3] suggested that inhabitants of cities with altitudes above 3,000 m a.s.l. are less susceptible to developing effects caused by COVID-19 due to ultraviolet radiation and thinner air.
Physiological factors can in uence the pathogenicity of SARS-CoV-2 at high altitudes. The barometric reading varies with changing weather conditions and becomes lower as the altitude increases. Thus, the volumes of inspired air, which require humidi cation, are much higher than at sea level, and the air density is lower at high altitudes [14]. As a result, compensatory adjustments to facilitate the release of oxygen to cells occur in individuals living at higher altitudes, such as the increase in the levels of 2,3-diphosphoglycerate (2,3-DPG), a chemical compound found inside the red blood cell, whose function is to reduce hemoglobin's a nity for oxygen in order to facilitate its release into tissues [15]. Given the above, a probable hypothesis for less severity in individuals infected with COVID-19 living in cities with higher altitude could be due to adaptations in these compensatory adjustments to increase the bioavailability of peripheral oxygen. This adaptation is proven in individuals who live at altitudes above 3,000 m a.s.l. In our study, RDR was higher at low altitudes. In this way, such adaptations, even to a lesser extent, could contribute to minimizing the severity of infection in cities located at higher altitudes.
The casual movement of dissolved oxygen molecules establishes the PO2 of plasma and tissue uids. The pressure of oxygen in the solution helps to regulate breathing, particularly at higher altitudes, when the ambient PO2 decreases considerably; it also determines the uptake of oxygen by haemoglobin in the lungs and the subsequent release into the tissues. However, haemoglobin saturation with oxygen changes very little until the oxygen pressure has decreased to about 60 mmHg. Even when alveolar PO2 drops to 75 mmHg, as it does at high altitudes, haemoglobin saturation decreases by only approximately 6%. At 60 mmHg alveolar PO2, haemoglobin is still 90% saturated with oxygen. Below that pressure, the volume of oxygen combined with haemoglobin decreases more quickly.
As exposed, the S shape of the oxyhaemoglobin dissociation curve indicates that there is only a small change in the percentage saturation of haemoglobin with oxygen up to an altitude of approximately 3,048 m. At 1,981 m, for example, the alveolar PO2 falls from its value at sea level from 100 mmHg to 78 mmHg. However, haemoglobin remains 90% saturated with oxygen. Given the above, considering that the Brazilian cities studied at a higher altitude are around 1100 m, probably the hypothesis of compensatory adjustments related to ACE2 in pulmonary epithelial cells, i.e., a protective factor for virus penetration and evolution of severe pulmonary edema, should be studied with caution in residents of Brazilian cities with higher altitudes. Furthermore, this population is also not exposed to conditions of chronic hypoxia.
Also, regarding the possible physiological factors, the receptor-binding domain (RBD) in the SARS-CoV-2 protein was recently identi ed and that the RBD protein-bound rmly to the receptors of the human angiotensin-converting enzyme 2 (ACE2) [16]. Human ACE2 is part of the renin-angiotensin system (RAS), an essential hormonal system for controlling blood pressure and uid and electrolyte balance. In the classical view, RAS peptides are generated from a single precursor protein called angiotensinogen (ATG). After being cleaved by the protease renin, this protein forms the inactive decapeptide angiotensin I, which is hydrolysed by the angiotensin-converting enzyme (ACE) and forms the octapeptide angiotensin II (Ang II), the principal peptide in the system. ACE2 cleaves a single residue of angiotensin I (Ang I) that generates the Ang-(1-9) peptide and degrades Ang II to the Ang-(1-7) vasodilator. Current data obtained during the pandemic suggest that the use of ACE inhibitors and angiotensin type I receptor blockers increase the expression of ACE2. Consequently, increased expression of ACE2 would facilitate infection by COVID-19 [17,18]. Studies show that RAS elements are modulated at high altitudes [19][20][21], the expression of the ACE2 enzyme can be down-regulated due to the high altitude favouring a lower incidence of COVID-19 infection.
The results presented in this work can be useful for the implementation of public policies for prevention, control of the dissemination of COVID-19 in Brazil and the world. Also, it can contribute to future studies, including other zoonotic viruses that cause respiratory diseases, as well as allowing the recommendation of changing the environment for people at risk in COVID-19.
Our ndings identi ed that virulence by SARS-CoV-2 is higher in Brazilian cities with a population above 200 thousand inhabitants, located at the lowest altitudes, and where the RH is highest (Fig. 3). These ndings are in line with the physiological compensatory adjustments of the inhabitants of cities located at higher altitudes, as well as with the common characteristics. Thus, our study starts point for future studies to establish causality of environmental conditions with SARS-CoV2, contributing to the implementation of measures to prevent and control the spread of COVID-19. It is, however, important to note that the information presented here clearly lacks any physiological evidences, which may merit further investigation. As prospective, longitudinal studies are needed to con rm whether these associations remain over time.

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Declarations ETHICS APPROVAL AND CONSENT TO PARTICIPATE Not applicable.

CONSENT FOR PUBLICATION
The researchers of this study con rm that they have given due consideration to protect the intellectual property associated with this work and that there are no impediments to publication, including the timing of publication, with respect to intellectual property. In so doing we con rm that we have followed the regulations of our institutions concerning intellectual property.

AVAILABILITY OF SUPPORTING DATA
The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.