From the Document: "[This] guidance is provided for definitions and management of contacts of people with COVID-19 [coronavirus disease 2019]. Separate guidance is available for international travelers. [...] Public health recommendations have been updated to accommodate new scientific evidence, evolving epidemiology, and the need to simplify risk assessment. New recommendations are based on:  Growing evidence of transmission risk from infected people without symptoms (asymptomatic) or before the onset of recognized symptoms (presymptomatic);  Increased community transmission in many parts of the country;  A need to communicate effectively to the general public; [and 4] Continued focus on reducing transmission through social distancing and other personal prevention strategies."
Centers for Disease Control and Prevention: https://www.cdc.gov/