SARS-CoV-2 in bats was transmitted to humans at a live and wet animal market in China through the intermediate host, creating COVID-19. Viral, environmental and host factors play roles in virus infection and disease. The virus has high transmissibility and is rapidly transmitted to people through close contact and droplets from coughing, sneezing and talking loudly, as well as through contact with contaminated objects. As crowding is an environmental risk factor for contamination, its transmission is high among patients and staff in hospital and also in elderly-care centers. It is more common in the elderly, in men, and subjects with diabetes mellitus, hypertension, cardiovascular disease, and malignancy.