Impact of outdoor and indoor meteorological conditions on the COVID-19 transmission in the western region of Saudi Arabia.

Meteorological conditions may influence the incidence of many infectious diseases. Coronavirus disease-2019 (COVID-19) is a highly contagious, air-borne, emerging, viral disease caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). In 2020, the COVID-19 global pandemic affected more than 210 countries and territories worldwide including Saudi Arabia. There are contradictory research papers about the correlation between meteorological parameters and incidence of COVID-19 in some countries worldwide. The current study investigates the impact of outdoor and indoor meteorological conditions on the daily recorded COVID-19 cases in western region (Makkah and Madinah cities) of Saudi Arabia over a period of 8 months from March to October 2020. Reports of the daily confirmed COVID-19 cases from the webpage of Saudi Ministry of Health (MOH) were used. Considering, the incubation period of COVID-19 which ranged from 2 to 14 days, the relationships between daily COVID-19 cases and outdoor meteorological factors (temperature, relative humidity, and wind speed) using a lag time of 10 days are investigated. The results showed that the highest daily COVID-19 cases in Makkah and Madinah were reported during the hottest months of the year (April-July 2020) when outdoor temperature ranged from 26.51 to 40.71 °C in Makkah and of 23.89-41.20 °C in Madinah, respectively. Partial negative correlation was detected between outdoor relative humidity and daily recorded COVID-19 cases. No obvious correlation could be demonstrated between wind speed and daily COVID-19 cases. This indicated that most of SARS-CoV-2 infection occurred in the cool, air-conditioned, dry, and bad-ventilated indoor environment in the investigated cities. These results will help the epidemiologists to understand the correlation between both outdoor and indoor meteorological conditions and SARS-CoV-2 transmissibility. These findings would be also a useful supplement to assist the local healthcare policymakers to implement and apply a specific preventive measures and education programs for controlling of COVID-19 transmission.

Introduction

In December 2019, an outbreak of atypical pneumonia caused by (severe acute respiratory syndrome-coronavirus-2 or SARS-CoV-2) was recorded for the first time in Wuhan, China (Huang et al., 2020; Wu et al., 2020; Zhou et al., 2020). The disease (coronavirus disease 2019 or COVID-19) was spread nationally and internationally (Callaway, 2020; Li et al., 2020). On March 11, 2020, the world health organization (WHO) was considered that COVID-19 is a pandemic (WHO, 2020). The international spreading of the disease has caused severe global public health challenges and worldwide economic problems (Phelan et al., 2020).

COVID-19 is easily transmitted between human beings with a basic reproductive number “R0” of about 2.2–3.1. The Causative virus (SARS-CoV-2) spreads through direct close contact with infected individual and exposure to expired droplets carrying infectious virus (CDC, 2021), aerosol infection (CDC, 2021; Anderson et al., 2020; Morawska and Milton, 2020), and indirect contact with contaminated fomites (Jing et al., 2020).

There are contradictory conclusions from previous research concerning influencing of outdoor meteorological conditions (temperature, relative humidity, and wind speed) on COVID-19 epidemiology. In China, there was a negative correlation between COVID-19 incidence and meteorological parameters (temperature and humidity) (Qi et al., 2020). On the other hand, analysis of meteorological data of 122 cities in China showed a 1 °C increase in the temperature (when <3 °C) was accompanied with an increase of 4.9% in the daily SARS-CoV-2 infected cases (Xie and Zhu, 2020).

Globally, it was concluded that both outdoor temperature and relative humidity were inversely correlated to the COVID-19 epidemiology (Sarkodie and Owusu, 2020). In New York, USA, there was a significant correlation between outdoor temperature and SARS-CoV-2 transmission (Bashir et al., 2020). In Spain, there was no significant association of SARS-CoV-2 transmission with the outdoor temperatures (Briz-Redóna and Serrano-Arocab, 2020). While in Barcelona, Spain, it was found that a 1 °C increase in the maximum outdoor temperature decreased the incidence rate of COVID-19 by 7.5% (Tobías and Molina, 2020). In Jakarta, Indonesia, there was a significant relationship between the average daily outdoor temperature and COVID-19 epidemiology (Tosepu et al., 2020).

In the optimum indoor meteorological conditions (temperature 23 °C, relative humidity 53%, without sunlight), the aerosolized SARS-CoV-2 may stay infectious for up to 16 h (Fears et al., 2020). It was suggested that SARS-CoV-2 contaminated surfaces may act as a source of infection for several hours to few days in indoor environments. At room temperature (24 °C), the virus can persist for 6.3–18.6 h depend upon the humidity but was stayed for only 1.0–8.9 h if the temperature increased to 35 °C (Biryukov et al., 2020).

It was found that both pre-symptomatic and asymptomatic COVID-19 infected cases have similar amounts of SARS-CoV-2 in the throat and nose in comparison with the symptomatic cases (Kim et al., 2020; Zou et al., 2020). Both pre-symptomatic and asymptomatic individuals can transmit SARS-CoV-2 (Sugano et al., 2020; Wei et al., 2020).

The seasonality of SARS-CoV-2 transmission is not yet fully understood. Due to the presence of many contradictory suggestions and conclusions concerning the relationship between meteorological parameters and COVID-19 daily incidence, the current study aimed to investigate the influence of indoor and outdoor meteorological parameters, including temperature, relative humidity, and wind speed) on the reported daily cases of COVID-19 in Makkah and Madinah cities, Saudi Arabia over a period of 8 months from March to October 2020, utilizing the meteorological network of Makkah and Madinah which belonging to Umm Al-Qura university. In addition to, the role of pre-symptomatic and asymptomatic infected individuals in spreading of SARS-CoV-2 especially in household environment was also discussed.

Materials and methods

Meteorological data

The climate of western region in Saudi Arabia (Makkah and Madinah) is characterized by desert climate with hot long summers and moderate short winters. Generally, the weather parameters were affected by the altitudinal and latitudinal zones of horizontal atmospheric convergence and divergence (Khan and Alghafari, 2018).

The influencing of temperature, humidity, and wind speed on the reported daily COVID-19 cases was investigated in two Holy cities (Makkah and Madinah) in the western region of Saudi Arabia, which attract annually Millions of Muslims from different countries worldwide to perform Hajj and Umrah. The two Holy cities are considered as hyper-arid areas. The investigations were carried out over a period of 8 months from March to October 2020 utilizing the meteorological network data of Makkah and Madinah which belonging to Umm Al-Qura university.

The meteorological data has collected and archived from the seven meteorological stations in Makkah network (Al-Sharra'a, Al-Laith, Azzizzaih, Al-Abdaih, Al-Takhsosy, Al-Nawaraih, and Kudy) distributed all-over Makkah City (Fig. 1 ), that belong to Umm Al-Qura university. Also concerning Madinah city, the network formalized by four meteorological stations (Failsaila, Khladia, Uhd and Qubaa) (Fig. 2 ). The measured parameters were quality controlled and statistically analysed, to perform the hourly average data (temperature, relative humidity, and wind speed).

Fig. 1

Location of the meteorological stations.

Fig. 2

Hourly average temperature during 2019 for (a) Makkah, and (b) Madinah cities.

The incubation period of COVID-19 is ranges from 2 to 14 days with an average of about 5 days (Linton et al., 2020). Qin et al. (2020) estimated COVID-19 incubation period between seven and eight days. Moreover, 2–3 days are needed for visiting the COVID-19 investigation center, sampling, and laboratory analysis results. Therefore, correlation between outdoor meteorological parameters and 10 days lagged daily infected COVID-19 cases was calculated, which was considered as the disease incubation period and time required for laboratory diagnosis.

Daily COVID-19 reported cases

Cumulative data with the daily number of recorded COVID-19 cases was obtained from the webpage of Saudi ministry of health (MOH) and World Health Organization (WHO). In Makkah, the investigations were carried out from 10th of March (date of the first reported COVID-19 case) to the end of October 2020. In Madinah, the investigations were started from 20th of March (date of the first confirmed SRAS-CoV-2 infected case) to the end of October 2020. Mathematical relationships curves, group of charts, and dispersion plots were prepared to explore the correlation of new daily COVID-19 cases and outdoor meteorological parameters of ten days ago in both Makkah and Madinah cities during a period of 8 months (dispersion plot is a scatter plot using Cartesian coordinates to display values for typically two variables for a set of data).

Results

Overview of outdoor meteorological condition in Makkah and Madinah

The average annual temperature in Makkah was about 32.73 °C, with a maximum hourly average of about 48.01 °C and minimum of 17.24 °C, which featured by moderate temperature in winter and drops to 25.36 °C (December to March) and hot in summer which rises to 36.76 °C (June to August). In Madinah, the average annual temperature was about 29.58 °C, with a maximum hourly average of about 46.35 °C and minimum of 9.64 °C, which featured by moderate temperature in winter and drops to 21.03 °C (December to March) and hot in summer which rises to 37.60 °C (June to August) (Fig. 2 a, b).

The average annual relative humidity in Makkah was about 34.61%, with a maximum hourly average of 87.30% and minimum of 4.08%, which featured by moderate relative humidity in winter by 47.20%, (December to March) and decreased in summer to 28.06% (June to August). In Madinah, the average annual relative humidity was about 24.58%, with a maximum hourly average of 94.00% and minimum of 3.77%, which featured by moderate relative humidity in winter by 35.37%, (December to March) and decreased in summer to 14.83% (June to August) (Fig. 3 a, b).

Fig. 3

Hourly average relative humidity during 2019 for (a) Makkah, and (b) Madinah cities.

The annual average wind speed reaches 1.51 and 1.52 m/s, with a maximum hourly average of 11.35, and 6.05 m/s in Makkah and Madinah, respectively. During summer season, the average wind speed reaches 1.46, 1.67 m/s, but during winter the average wind speed reaches 1.76, 1.42 m/s in Makkah and Madinah, respectively.

Correlation of outdoor meteorological conditions and COVID-19 daily cases in Makkah

During the period 10 March - 31 October 2020, a group of charts were constructed to obtain the mathematical relationships between the reported daily COVID-19 cases and outdoor meteorological conditions (temperature, relative humidity and wind speed) of ten days ago in Makkah and Madinah cities.

It is evident from the relationships between daily COVID-19 cases and outdoor average temperature during the period (10 March – 31 October 2020), there was no observed correlation in Makkah and Madinah cities, where the outdoor temperature ranging between 24.00 and 40.71 °C in Makkah with the average of 34.19 °C, and in Madinah city with a range of 19.60–41.20 °C by the average of 33.52 °C (Fig. 4 a, b), supported with the dispersion curves that performed a not significant relationship (Fig. 5 a, b).

Fig. 4

Relation between daily COVID-19 cases and average temperature of 10 days ago in (a) Makkah and (b) Madinah cities. (Poly. means polynomial average).

Fig. 5

Dispersion plot of daily COVID-19 cases and average temperature of 10 days ago in (a) Makkah and (b) Madinah cities (grey dots show the scattered data, and red dots display the average trend of the concerned parameters). (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Outdoor relative humidity ranging between 8.63 and 57.84% in Makkah with the average of 27.91%, and in Madinah city with a range of 6.25%–44.20% by the average of 18.31%. Regarding the relationship between daily infected COVID-19 cases and outdoor relative humidity of ten days ago in Makkah and Madinah cities, it is well observed, the divergence between the daily COVID-19 cases in Makkah and Madinah cities and the outdoor relative humidity (i.e. on more humid conditions than 30% as an average intercepted with high reported daily COVID-19 cases). While during the period 18 April – 14 June 2020, the outdoor relative humidity was decreased to an average of 23.53%, which meet an acceptable correlation with the daily COVID-19 cases in Makkah and Madinah cities (the intersection of the polynomial average of COVID-19 cases and RH) (Fig. 6 a, b). Finally, the dispersion curves showed a nearly inverse relationship between outdoor relative humidity and daily COVID-19 cases in Makkah and Madinah cities as a total relationship during the correlated period (Fig. 7 a, b).

Fig. 6

Relation between daily COVID-19 cases and average relative humidity of 10 days ago in (a) Makkah and (b) Madinah cities (Poly. means polynomial average).

Fig. 7

Dispersion plot of daily COVID-19 cases and average relative humidity of 10 days ago in (a) Makkah (b) Madinah cities (green dots show the scattered data, and red dots display the average trend of the concerned parameters). (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

The inspection of relation between daily COVID-19 cases and outdoor wind speed of ten days ago in Makkah and Madinah cities during the period (01 March – 21 October 2020) didn't show any obvious relationship (Fig. 8 a, b). Outdoor wind speed ranging between 0.59 and 2.98 m/s in Makkah with the average of 1.52 m/s and in Madinah city with a range of 0.93–3.22 m/s by the average of 1.79 m/s (Fig. 8 a, b), the dispersion curves showed a nearly direct relationship between outdoor wind speed and daily COVID-19 cases in Makkah and Madinah cities as a total relationship during the correlated period (Fig. 9 a, b).

Fig. 8

Relation between daily COVID-19 cases and average wind speed of 10 days ago in (a) Makkah and (b) Madinah cities (Poly. means polynomial average).

Fig. 9

Dispersion plot of daily COVID-19 cases and average wind speed of 10 days ago in (a) Makkah and (b) Madinah cities (blue dots show the scattered data, and red dots display the average trend of the concerned parameters). (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Overview of the indoor meteorological conditions in Makkah and Madinah

Our findings indicated that most of SARS-CoV-2 infection occurred in the cool, dry, air-conditioned, and bad-ventilated indoor environment in both Makkah and Madinah. Very hot weather in the western region of Saudi Arabia leads to intensive use of air-conditions along the summer months. Subsequently, this leads to cool (20–24 °C), dry (20–30% RH), and poorly ventilated indoor environment in both Makkah and Madinah. As suggested by some cluster infection, close-contact aerosol transmission is likely to be combined with respiratory droplets in a confined, poorly ventilated, and crowded indoor environment.

It was suggested that both pre-symptomatic and asymptomatic individuals played a great role in SARS-CoV-2 transmission in the household. Both pre-symptomatic and asymptomatic individuals are acting as unknown common source of infection for the others. Direct contact with such unidentified infected persons may facilitate the COVID-19 spread especially within the suitable indoor meteorological conditions in both Makkah and Madinah cities.

Discussion

The seasonality of SARS-CoV-2 transmission is not yet fully understood. Globally, meteorological factors may play a role in SARS-CoV-2 spread. This role may result only in comparatively slower spread of SARS-CoV-2, but not stopped it (Bukhari et al., 2020). On a worldwide scale, it was revealed that combination of temperature, relative humidity and wind speed can forecast the situation of COVID-19 pandemic (Chen et al., 2020).

There may be a negative association of the local outdoor temperature of a country with the reported COVID-19 cases (Jin et al., 2020). In a comparative study in five cities in Saudi Arabia, a negative correlation was detected between the meteorological factors (temperature, humidity, and wind speed) and SARS-CoV-2 spreading (Alkhowailed et al., 2020). In the present study, no correlation could be detected between the daily recorded COVID-19 cases and the atmospheric temperature of ten days ago in both Makkah and Madinah cities. While many other studies reported negative association of COVID-19 cases and the temperature. This indicting that negative or positive correlation between outdoor temperature and incidence of COVID-19 is depending on the geography and the meteorological condition in each country worldwide. This may explain the presence of many contradictory conclusions and suggestions about the influence of atmospheric temperature on COVID-19 epidemiology. In Mexico, the regional variations of climate factors influenced the trend of the local SARS-CoV-2 transmission rate. Tropical climate delayed the onset of the virus transmission, while the onset was rapidly present in tempered climates. So that, the regional climate characteristics are correlated significantly with local SARS-CoV-2 infection rate (Méndez-Arriaga 2020). In the (sub) tropical cities of Brazil, there was negative linear correlation between temperature and COVID-19 confirmed cases (Prata et al., 2020).

In most COVID-19 affected countries, there was a reverse association between country average temperature and COVID-19 cases (Sobral et al., 2020). The findings of the current study showed no correlation between the new daily COVID-19 cases and outdoor atmospheric temperature of ten days ago in the western region of Saudi Arabia. The incidence of the disease was the highest during the hottest months of the year from April to July with an average outdoor temperature of 34.93 °C and 34.5 °C in Makkah and Madinah, respectively. So that temperature alone cannot be the scalarly factor for SARS-CoV-2 spreading. In London, UK it was concluded that meteorological factors (daily average temperature, humidity, and wind speed) alone cannot used for determination of the changes in the number of COVID-19 cases (Ghosh et al., 2020).

It was suggested that relative humidity may more influence SARS-CoV-2 transmission than temperature in tropical countries and temperate zone (Yuan et al., 2020). in Singapore, SARS-CoV-2 transmission had positive association with the temperature and humidity (Pani et al., 2020). While weak positive association of new COVID-19 cases with relative humidity was also detected in Kuala Lumpur, Malaysia (Suhaimi et al., 2020). In the current study, mathematical linear curves showed weak evidence of negative correlation between outdoor relative humidity and new COVID-19 cases in both Makkah and Madinah. Beside to the absence of correlation between the outdoor temperature with the daily COVID-19 cases in the two investigated cities (Makkah and Madinah). This agreed with the conclusion of Ghosh et al. (2020) who proofed that climatic factors cannot be used as accurate tool to determine the changes of COVID-19 incidence.

High wind speeds facilitate airborne transmission of SARS-CoV-2 (Dbouka and Drikakisb, 2020). In this study, mathematical relationships curves showed no obvious correlation between the COVID-19 cases and wind speed. While, in general the dispersion curves showed a nearly direct relationship between outdoor wind speed and daily COVID-19 cases as a total relationship during the correlated period in Makkah and Madinah cities. In Turkey, there was positive correlation of the COVID-19 cases with the wind speed. The wind speed 14 days ago had the highest association with COVID-19 cases (Şahin, 2020). In Delhi, India there was also positive association of COVID-19 cases and wind speed (Singh et al., 2020).

Studying of weather impact on the SARS-CoV-2 aerosol survival revealed significant decrease in airborne virus survival in both low relative humidity and high temperature (Dbouka and Drikakisb, 2020). A significant reduction in COVID-19 daily morbidities and fatalities was detected in world's top ten hottest countries with high outdoor temperature and low outdoor relative humidity, including Saudi Arabia, compared to the coldest countries with low temperature and high relative humidity. This indicates the correlation between COVID-19 epidemiological pattern and mereological factors (Meo et al., 2020). While in the present study, the peak of COVID-19 daily cases was reported during the hottest months of the year (April to July). This indicated that almost all COVID-19 cases in the two investigated cities were occurred within the indoor environment with air-conditioned cool indoor temperature (20–25 °C) and the relative humidity of (20–30%). Yuan et al. (2020) stated that dry and cool conditions may facilitate the SARS-CoV-2 spreading. It was found that most SARS-CoV-2 transmission has occurred in indoor environments in China (Qian et al., 2020) and Japan (Azuma et al., 2020).

Both droplets and aerosols expired by SARS-CoV-2-infected individuals are the source of the airborne infection to the others (Jayaweera et al., 2020). Such infection is more common in bad ventilated confined areas with suitable temperature and humidity (Han, 2020; Jayaweera et al., 2020). Also, SARS-CoV-2 may survive for several days in an arid and cool condition (Yuan et al., 2020). Therefore, intensive using of the air conditions especially during the summer season in both Makkah and Madinah led to bad ventilated indoor environment which facilitated the SARS-CoV-2 transmission. Harmooshi et al. (2020) stated that that low temperatures, as well as dry and unventilated air, may influence SARS-CoV-2 stability and transmissibility. The chances of airborne SARS-CoV-2 transmission are higher in dry indoor places (<40% RH) than in humid places (>90% RH). It is necessary to set a minimum RH standard for minimizing of indoor SARS-CoV-2 spread (Ahlawat et al., 2020). Improvement of the indoor air environments such as sufficient ventilation and setting the minimum standard of RH could be beneficial in limiting indoors ARAS-CoV-2 infection risk (Noorimotlagh et al., 2021).

Both pre-symptomatic (Han 2020; Kong et al., 2020) and asymptomatic (Bai et al., 2020; Sugano et al., 2020) infected individuals can transmit the disease. Our study suggested that both pre-symptomatic and asymptomatic cases, which act as unknown and common source of infection, play a great role in SARS-CoV-2 spreading within the suitable indoor environment in both Makkah and Madinah cities. It was estimated that about 12% of COVID-19 cases are due to asymptomatic transmission (Du et al., 2020). Also, it was found that 15–56% of the SARS-CoV-2 infected cases are resulted from pre-symptomatic transmission (Liu et al., 2020; Zhang et al., 2020).

COVID-19 is transmitted rapidly with high infection rate within the family clusters (Song et al., 2020). The infection rate of SARS-C0V-2 was higher among close contacts within households than casual contacts (Shen et al., 2020). The current study suggested that direct contacts between infected and non-infected individuals within the households, especially in case of large indoor gatherings, in the western region of Saudi Arabia facilitated the spread of SARS-CoV-2 infection. This agrees with Leclerc et al. (2020) who mentioned that clusters of COVID-19 cases are often associated with large indoors gatherings.

There are many human factors affecting the SRSA-CoV-2 spreading e.g., control measurements implementation, contact tracing application, case finding efficiency, quarantine strategic plans, medical resources ability and urbanization rate (Yuan et al., 2020). Lockdown and implementation of social contact restriction reduced COVID-19 daily incidence in both Italy and Spain (Tobías 2020). In Saudi Arabia, early control interventions and implementation of strict control measurements helped the suppressing of COVID-19 pandemic curve. Physical distancing, face masks, and eye protection are necessaries to prevent SARS-CoV-2 transmission between individuals in community settings (Chu et al., 2020). West et al. (2020) stated that changes of some behaviors may limit, and control COVID-19 spread. The current study suggested that, beside to the general preventive measurements of COVID-19 pandemic, a group of certain control measures are necessary for each country and community according to the social behaviors and culture of the public. In addition to the strict applied control measurements in Saudi Arabia, a specific interventions and education programs are necessary to avoid the clusters SARS-CoV-2 infection among the households within the suitable indoor environmental conditions.

Conclusion

In conclusion, there is no evidence of a direct correlation between outdoor temperature and the daily reported cases of COVID-19 in the western region of Saudi Arabia (Makkah and Madinah cities) during the period from March to October 2020. A partial negative association of the outdoor relative humidity and wind speed with the daily recorded COVID-19 cases was detected. It was indicated that most of the SARS-CoV-2 infection was occurred within the households in a cool, air-conditioned, dry, and bad-ventilated indoor environmental conditions. It was suggested that the outdoor SARS-CoV-2 infection may be very rare and occur to lesser extent in comparison to the indoor infection in both Makkah and Madinah cities. Hot outdoor weather creates cool, dry, and bad-ventilated indoor environment which facilitate droplet and aerosol SARS-CoV-2 infection among the households especially in the presence of pre-symptomatic and asymptomatic infected individuals. Social gatherings at a suitable indoor environment may be the main cause of SARS-CoV-2 transmission in the western region of Saudi Arabia. Adoption of preventive measures, implementation of stringent precautionary measures, strict application of control strategic plans, populations knowledge and social behavior as well as both indoor and outdoor environmental conditions are important factors in the spread rate and control of COVID-19. In addition to the general known measurements for controlling of SARS-CoV-2 infection, some other specific preventive measures and education programs should be implemented and applied in each country according to its geography, both indoor and outdoor meteorological conditions and social behaviors of the public. The results of the current study may guide health authorities in Saudi Arabia for implementation of specific precautionary measures to limit the indoor SARS-CoV-2 infection. Prevention of indoor infection may control COVID-19 spreading in tropical and hyper-arid countries.

Credit author statement

Turki M. Habeebullah: Supervision. Ibrahim H.A. Abd El-Rahim: Conceptualization, Investigation, Data Collection, Visualization, Writing – review & editing. Essam A. Morsy: Conceptualization, Investigation, Data Collection, Visualization, Writing – review & editing.

Funding

This work was supported by the Deanship of Scientific Research at (grant number: 20-MED-4-13-0014).

Ethical approval

Not required.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.