Please tell me why the Changzhou health code I returned to Sichuan on the 1st of this month turned into a yellow code when I arrived on the 3rd.

＜strong＞The reasons are as follows: ＜/strong＞

The health code turns into a yellow code for the following reasons: 1. A confirmed case of COVID-19 is found in the area where it is located, and it is classified into a control area. Within the control area, the health code of personnel belonging to the control area is assigned a yellow code. 2. The health codes of people whose trajectories are suspected to overlap with those of confirmed COVID-19 cases will be updated to yellow codes. For example, the health codes of contacts and time and space companions of sub-close contacts will be assigned yellow codes. 3. You have been to areas with medium and high risks of the epidemic, such as co-investigators in epidemic areas and people in medium-risk areas with yellow health codes in the past 14 days. 4. All employees are required to undergo nucleic acid testing, but if nucleic acid testing is not performed, the health code will be assigned a yellow code. 5. The identity information of the personal mobile phone number matches the person assigned the yellow code. 6. People who self-reported health information appeared: fever, shortness of breath, respiratory symptoms information. 7. Persons who are confirmed cases within 14 days after being cured and discharged from hospital, within 14 days after asymptomatic infections are released from isolation, and within 14 days after suspected cases are eliminated.