A female client develops a cough, new loss of taste or smell…

A female client develops a cough, new loss of taste or smell, and fever. She had been in an office and touched a  door knob that the person ahead of her had coughed into their hand and opened the door.  The female client tests positive for COVID-19,  In this situation, the SARS-CoV-2 is which component of the epidemiological triangle?