Effect of environmental factors on SARS-CoV-2 infectivity in northern hemisphere countries: a 2-year data analysis

OBJECTIVE

The COVID-19 pandemic that emerged in December 2019 brought human life to a standstill. With over 2-year since the pandemic originated from Wuhan, SARS-CoV-2 has caused more than 6 million deaths worldwide. With the emergence of mutant strains and COVID-19 surge waves, it becomes critically important to conduct epidemiological studies that allow us to understand the role of various environmental factors on SARS-CoV-2 infectivity. Our earlier study reported a strong negative correlation between temperature and COVID-19 incidence. This research is an extension of our previous study with an attempt to understand the global analysis of COVID-19 in northern hemisphere countries.

STUDY DESIGN

This research aims at achieving a better understanding of the correlation of environmental factors such as temperature, sunlight, and humidity with new cases of COVID-19 in northern hemisphere from March 2020 to February 2022.

METHODS

To understand the relationship between the different environmental variants and COVID-19, a statistical approach was employed using Pearson, Spearman and Kendall analysis.

RESULTS

Month-wise univariate analysis indicated a strong negative correlation of temperature and sunlight with SARS-CoV-2 infectivity, whereas inconsistencies were observed in correlation analysis in the case of humidity in winter months. Moreover, a strong negative correlation between average temperature of winter months and COVID-19 cases exists as evidenced by Pearson, Spearman, and Kendall analyses. In addition, correlation pattern between monthly temperature and COVID-19 cases of a country mimics to that of sunlight of a country.

CONCLUSION

This pilot study proposes that low temperatures and low sunlight might be additional risk factors for SARS-CoV-2 infectivity, mostly in northern hemisphere countries.

Temporal and spatial analysis of COVID-19 transmission in China and its influencing factors

OBJECTIVES

The purpose of this study was to explore the temporal and spatial characteristics of COVID-19 transmission and its influencing factors in China, from January to October 2020.

METHODS

About 81,000 COVID-19 confirmed case data, Baidu migration index data, air pollutants, meteorological data, and government response strictness index data were collected from 31 provincial-level regions (excluding Hong Kong, Macao, and Taiwan) and 337 prefecture-level cities. The spatio-temporal characteristics of COVID-19 were explored using spatial autocorrelation, hot spot, and spatio-temporal scanning statistics. At the same time, Spearman rank correlation analysis and multiple linear regression were used to explore the relationship between influencing factors and confirmed COVID-19 cases.

RESULTS

The distribution of COVID-19 in China tends to be stable over time, with spatial correlation and prominent clustering regions. Spatio-temporal scanning analysis showed that most COVID-19 high-incidence months were from January to March at the beginning of the epidemic, and the area with the highest aggregation risk was Hubei Province (RR=491.57) which was 491.57 times the aggregation risk of other regions. Among the meteorological variables, the daily average temperature, wind speed, precipitation, and new COVID-19 cases were negatively correlated. The air pollution concentration and migration index were positively correlated with new confirmed cases, and the government response strict index was strongly negatively correlated with confirmed COVID-19 cases.

CONCLUSIONS

Environmental temperature has a certain inhibitory effect on the transmission of COVID-19; the air pollution concentration and migration index have a certain promoting effect on the transmission of COVID-19. The strict government response index indicates that the greater the intensity of government intervention, the fewer COVID-19 cases will occur.

Effects of Environmental Temperature and Dietary Fat Content on The Performance and Heat Production and Substrate Oxidation in Growing Pigs

This study aimed to evaluate the effect of temperature and dietary fat level on growth performance, heat production, nutrient oxidation and nitrogen balance in growing pigs. Thirty-two pigs (Duroc × Landrace × Large White) with initial weight of 25±1.91 kg were assigned to treatments in 2×4 factorial design. All pigs were fed with two isoenergetic and isoproteic diets of different fat levels (low fat level: 3.68% fat of dry matter (DM) and high fat level: 8.39% fat of DM) under four environmental temperatures (23, 18, 13 and 8 ºC). Heat production (HP) and nutrient oxidation were calculated from gas exchange via measurement with respiration chambers. The results showed that there was no interaction effect on growth performance by the temperature and dietary fat level. The average daily feed intake (ADFI) was lower (P < 0.001), the average daily gain (ADG) was higher (P < 0.001) and feed utilization was more efficient at 23 ºC than 13 and 8 ºC (P < 0.001). Dietary fat had no effect on growth performance and feed utilization at the four different temperatures. A significant interaction (P < 0.001) between temperature and dietary fat level on oxidation of carbohydrate (OXCHO) and fat (OXF) was observed. HP, OXF and OXCHO were significantly increased (P < 0.001) as environment temperatures decreased. Increasing dietary fat generated an increase in the OXF and decrease in the OXCHO (P < 0.001). No significant difference was observed in protein oxidation (OXP) of two factors. The intakes of nitrogen, nitrogen excretion in feces (FN) and urine (UN) by the pigs kept in 8 ºC environment were highest. Nitrogen digestibility decreased as environmental temperature decreased, with the most efficient gains obtained at 23 ºC. However, nitrogen retention was not influenced by environmental temperature. Dietary fat level did not affect nitrogen balance. No significant interaction between temperature and dietary fat level was observed for nitrogen balance. These results indicated that the rate of growth and nutrition utilization in pigs fed ad libitum are influenced by the environmental temperatures in which they are maintained, and the oxidation of nutrition utilization of the pig to different environmental temperatures is altered by the dietary fat supplementation.