For patients in the general medical unit who satisfy the inclusion and exclusion criteria, the matching characteristics will be assessed and if there is a match in the pool of case group patients, the patient will be enrolled. If there is no successful match in the case group patients, we will enroll the patient to the pool of control group patients if the pool of control group patients is fewer than a predetermined size of 10 patients; or if the pool of control group patients is more than 10 patients, we will enroll the patient randomly by a predetermined probability to be in the pool of control group patients.