For the purposes of this study, close contacts were defined as individuals that had unprotected close contact with a confirmed case within 2 days before their symptom onset or sample collection.

Household contacts were designated one of two groups - Definition One: Those who were either family members or close relatives, such as parents and parents-in-law., regardless of address. - Definition Two: Those living at the same address regardless of relationship.

All close contacts were place under quarantine measures that involved confining them to designated places, such as hotel rooms or at home. Each person was followed up for 14 days and tested by RT-PCR at days 1 and 14.

All close contact that were considered a local case with symptom onset 1 day or less, or 3 days or less for an imported case, from the earliest onset day in the close contact group were considered primary cases.