Factors determining the diffusion of COVID-19 and suggested strategy to prevent future accelerated viral infectivity similar to COVID

Abstract

This study has two goals. The first is to explain the geo-environmental determinants of the accelerated diffusion of COVID-19 that is generating a high level of deaths. The second is to suggest a strategy to cope with future epidemic threats similar to COVID-19 having an accelerated viral infectivity in society. Using data on sample of N = 55 Italian province capitals, and data of infected individuals at as of April 7th, 2020, results reveal that the accelerate and vast diffusion of COVID-19 in North Italy has a high association with air pollution of cities measured with days exceeding the limits set for PM₁₀ (particulate matter 10 μm or less in diameter) or ozone. In particular, hinterland cities with average high number of days exceeding the limits set for PM₁₀ (and also having a low wind speed) have a very high number of infected people on 7th April 2020 (arithmetic mean is about 2200 infected individuals, with average polluted days greater than 80 days per year), whereas coastal cities also having days exceeding the limits set for PM₁₀ or ozone but with high wind speed have about 944.70 average infected individuals, with about 60 average polluted days per year; moreover, cities having more than 100 days of air pollution (exceeding the limits set for PM₁₀), they have a very high average number of infected people (about 3350 infected individuals, 7th April 2020), whereas cities having less than 100 days of air pollution per year, they have a lower average number of infected people (about 1014 individuals). The findings here also suggest that to minimize the impact of future epidemics similar to COVID-19, the max number of days per year that Italian provincial capitals or similar industrialized cities can exceed the limits set for PM₁₀ or for ozone, considering their meteorological conditions, is about 48 days. Moreover, results here reveal that the explanatory variable of air pollution in cities seems to be a more important predictor in the initial phase of diffusion of viral infectivity (on 17th March 2020, b₁ = 1.27, p < 0.001) than interpersonal contacts (b₂ = 0.31, p < 0.05). In the second phase of maturity of the transmission dynamics of COVID-19, air pollution reduces intensity (on 7th April 2020 with b'₁ = 0.81, p < 0.001) also because of the indirect effect of lockdown, whereas regression coefficient of transmission based on interpersonal contacts has a stable level (b'₂ = 0.31, p < 0.01). This result reveals that accelerated transmission dynamics of COVID-19 is due to mainly to the mechanism of "air pollution-to-human transmission" (airborne viral infectivity) rather than "human-to-human transmission". Overall, then, transmission dynamics of viral infectivity, such as COVID-19, is due to systemic causes: general factors that are the same for all regions (e.g., biological characteristics of virus, incubation period, etc.) and specific factors which are different for each region and/or city (e.g., complex interaction between air pollution, meteorological conditions and biological characteristics of viral infectivity) and health level of individuals (habits, immune system, age, sex, etc.). Lessons learned for COVID-19 in the case study here suggest that a proactive strategy to cope with future epidemics is also to apply especially an environmental and sustainable policy based on reduction of levels of air pollution mainly in hinterland and polluting cities- (having low wind speed, high percentage of moisture and number of fog days) -that seem to have an environment that foster a fast transmission dynamics of viral infectivity in society. Hence, in the presence of polluting industrialization in regions that can trigger the mechanism of air pollution-to-human transmission dynamics of viral infectivity, this study must conclude that a comprehensive strategy to prevent future epidemics similar to COVID-19 has to be also designed in environmental and socioeconomic terms, that is also based on sustainability science and environmental science, and not only in terms of biology, medicine, healthcare and health sector.

Keywords: Air Pollution; Airborne Transmission; Airborne disease; COVID-19; Coronavirus Infection; Disease Transmission; Epidemic Outbreak; Infection Prevention; Lung Disease; Opportunistic pathogen; Pandemic; Particulate Matter; Quarantine; SARS Coronavirus; SARS-CoV-2; Severe Acute Respiratory Syndrome Coronavirus 2; Transmission Dynamics; Viral infectivity; Virus Pneumonia; Virus Transmission.

Graphical abstract

Fig. 1

Regression line of Log Infected individuals 7th April, 2020 on Log Density inhabitants/km² 2019, considering the groups of cities with days exceeding limits set for PM₁₀ or ozone <, or ≥100 days. Note: This result reveals that transmission dynamics of COVID-19 is due to two mechanisms given by: human-to-human transmission (based on density of population) and air pollution-to-human transmission (airborne viral infectivity); in particular, in polluting cities, the accelerated diffusion of viral infectivity is also due to mechanism of air pollution-to-human transmission that may have a stronger effect than human-to-human transmission!

Fig. 2

Estimated relationship of number of infected on days exceeding limits of PM₁₀ in Italian provincial capitals (Quadratic model).

Fig. 3

COVID-19 Outbreak (number of infected individual on 26 April 2020) and days exceeding the limits set for PM₁₀ or ozone.

Fig. 4

Reduction Nitrogen Dioxide before (January 2020) and during lockdown (February–March 2020) because of COVID-19 Outbreak in Italy.

Fig. 1A

Regression line of Log Infected 7th April, 2020 on Log days exceeding limits set for PM₁₀ or ozone according to density of population per km² in Italian province capitals, N = 55 (3 categories: <500, 500–1500, >1500 inhabitants per km²). Note: This result confirms that transmission dynamics of COVID-19 increases with the mechanism of air pollution-to-human transmission, but the rate of growth of Coronavirus disease is higher in the presence of a high density of population (i.e., >1500 inhabitants per km²) because of the mechanisms of human-to-human transmission.