As there is no vaccine and appropriate drugs for treatment of the novel Coronavirus Disease (COVID-19), one of the fundamental problems is the evaluation of environmental and social weaknesses of cities/regions to the exposure of infectious diseases for preventing and/or containing new COVID-19 outbreaks and of other viral agents that generate negative impact on public health and economy of countries. The current monitoring of transmission dynamics of infectious diseases is mainly based on reproduction number (R) and fatality rates. However, this approach is a real-time monitoring of transmission dynamics for mitigating the numbers of COVID-19 related infected individuals and deaths. Reproduction number does not provide information to cope with future epidemics or pandemic. The main goal of this study is to propose the index c (as contagions) that quantifies, ex-ante, the environmental risk of exposure of cities/regions to future epidemics of the COVID-19 and similar vital agents. This index c synthetizes environmental, demographic, climatological and health risk factors of cities/regions that assess their exposure to infectious diseases. Index c has a range from 1 (environmental and social weakness of the urban area leading to high levels of exposure to infectious diseases and deaths) to 0 (environment that reduces the risk of exposure to infectious diseases in society). The statistical evidence here, applied on case study of Italy, seems in general to support the predictive capacity of the index c as a particularly simple but superior indicator in detecting the global correlation between potential risk of exposure of cities/regions to infectious diseases and actual risk given by infected individuals and deaths of the COVID-19. The index c can support a proactive environmental strategy to help policymakers firstly to prevent future pandemic similar to the COVID-19 and, in case of diffusion of infectious disease beyond the initial outbreak, to constrain infected individuals and deaths with appropriate control measures of containment and mitigation in society.Copyright © 2020. Published by Elsevier Inc.