Introduction
Following the first COVID-19 case in Wuhan, China in December 2019, the disease spread rapidly to over 60 countries in early 2020. Consequently, the World Health Organization (WHO) declared a pandemic on March 12, 2020, within 71 days of the first case (Zhu et al., 2020, World Health Organization, 2020c, World Health Organization, 2020d, World Health Organization, 2020e). As of March 31, COVID-19 was present in 206 countries, with 770 138 confirmed patients and 36 796 deaths worldwide (WHO, 2020b). Different countries are employing diverse methods to manage and prevent the further spread of COVID-19 (WHO, 2020a). Most countries are limiting contact between citizens, most notably China, where Wuhan was placed under lockdown within just 23 days of the outbreak, and contact with neighboring cities was forbidden (Lin et al., 2020). France, Switzerland, and Austria closed their borders on March 17, while France, Spain, Italy, Germany, and some states in the US have been implementing strict policies to limit contact between citizens, including nationwide stay-at-home orders, thereby preventing the domestic spread of COVID-19 (Kinross et al., 2020).
South Korea’s total population is 51.8 million, of which a large proportion resides or is active in the capital and the surrounding Gyeonggi Province. Of the total population, 13.28 million (26.0%), 9.73 million (18.7%), and 2.95 million (5.7%) reside in Gyeonggi Province, Seoul, and Incheon, respectively (Resident, 2020). Several studies have indicated that these densely populated urban environments and the heavy dependence on public transport could increase the potential spread of COVID-19 (Choi and Ki, 2020, Korean Society of Infectious Diseases et al., 2020, BBC News, 2020, Shim et al., 2020). On March 2, the South Korean government initially postponed the commencement of elementary, middle, and high schools for 4 weeks until April 6, and of university classes until March 16, before switching to online classes until April 16. Some schools decided to conduct online classes for the entire first semester (Koh and Hoenig, 2020). Due to joint efforts, including public institutions, private enterprises, and other companies implementing work-from-home systems to minimize travel, preventive education for citizens via social distancing campaigns, availability of disinfectant in every building and street, and transparency of information regarding the movements and locations of confirmed patients, a decreasing trend is being observed in the daily number of new COVID-19 patients.
Based on existing studies, although the number of new COVID-19 patients in South Korea shows a decreasing trend, the global number of COVID-19 cases, including South Korea, is forecast to eventually increase again, possibly due to genetic mutations in the virus, re-influx from overseas, and decreasing compliance by the public (Liu et al., 2020, Verity et al., 2020, Zhan et al., 2020). In particular, unlike in Spain, the US, and the UK, outdoor excursions are not restricted in South Korea. Therefore, it is predicted that, as citizens adapt to COVID-19, activity levels will increase and adherence will decrease for measures such as staying indoors, social distancing, and mask wearing, resulting in a secondary outbreak of COVID-19 (Zhan et al., 2020). Research analyzing 10 years of data has found a strong correlation between infectious diseases and traffic volume; specifically, increased traffic during an infectious disease outbreak is associated with greater spread (Meloni et al., 2009, Wu et al., 2019). An analysis of 10 types of influenza from the last 300 years showed a very close association with traffic. A disease that took 1 year to spread 300 years ago would now be able to reach anywhere in the world within a day, due to developments in travel (Rodrigue et al., 2020).
This study investigated the association between changes in traffic volume and the spread of COVID-19 in South Korea, and provides predictive data that may be required to guide future infectious disease prevention policies.