while going through some literature, i developed a picturisation in my mind. the incident of coronavirus mutating into human body may date back before November 19.. maybe it was an ongoing process. they may have slowly infiltrated into the workers in the market and mutated in their body... but maybe because they were strong individuals with good immunity, they may only have had some flu symptoms, the first wave of coronavirus in human, which may have been weak, against which the workers may have gained immunity rapidly and easily.. but the virus persisted and again mutated and become strong... and when it affected ordinary elder people with low immunity, the virus may have become fatal.. and being highly contagious as it was, lead to what we are seeing now.. this is my theory..