Diseases that spread through aerosols , droplets , or fomites are often transmitted widely in crowded environments . Therefore , social distancing has been a key feature of prevention strategies for coronavirus disease 2019 . Despite these efforts , as of July 2021 the COVID-19 pandemic directly led to over 600,000 deaths in the US according to Johns Hopkins Center for Systems Science and Engineering 's continually updated dashboard ( Dong et al . , 2021 ) . One important aspect of outbreak prevention involves targeting locations with increased transmission rates with information , testing , and other preventative or assessment measures . Although transmission rates of novel diseases are generally estimated on a population level , an emerging epidemic of such a disease can be challenging to characterize because the key analytic parameters estimated by early studies are specific to the initial outbreak 's population . If ungeneralizable data are used to model transmission rates , it is possible that inadequate resources will be allocated to locations with greater disease burden ( Jewell et al . , 2020 ) .