According to government officials, the virus was brought into the estate by an infected kidney patient (the type of kidney illness was not specified) after discharge from Prince of Wales Hospital, who visited his elder brother living on the seventh floor. Through excretion, the virus spread through drainage. One theory speculated that the virus was spread by airborne transmission, through dried up U-shaped P-traps in the drainage system which a maritime breeze blew into the estate's balconies and stairwell ventilation.