What does it mean to be a potential close contact of a positive person (in the same carriage)?

Potential associates of positive people refer to people who have close contact with positive people in COVID-19 and may have time and space intersection. The same car is at risk of infection. The common symptoms in COVID-19 are fever, dry cough, fatigue, sore throat, decreased sense of smell and taste, stuffy nose, runny nose, conjunctivitis, myalgia and diarrhea, with different severity.