Results
COVID-19 contact investigation and management comprised of the following: 1) determination of the location of the contact (patient route), 2) exposure risk evaluation, 3) contact classification, and 4) contact management. The location of the contact was determined through the process of preliminary identification, by interviewing patients, and their acquaintances, and by objective verification of the investigated information. Exposure risk evaluation was performed depending on the route of disease transmission, patient characteristics, and environmental characteristics. Based on the results of the evaluation, the contacts were classified into close and casual contacts depending on the exposure [4]. The method of managing the classified contacts was largely distinguished between movement restriction and symptom monitoring. Movement restriction is a legal public health order, and quarantine (isolation), home isolation, or controlled travel is enacted. Symptom monitoring was performed as either active or passive monitoring, depending on the exposure risk (Figure 1).
The methods used to overcome recall and confirmation biases that can occur while determining the location of the contact include checking medical facilities records, phone-based global positioning system (GPS), card transaction records, and closed-circuit television (CCTV; Table 1).

1. History of using medical facilities and visiting pharmacies
History of using medical facilities, and visiting pharmacies was used to estimate the window of time of infection, through an accurate evaluation of the clinical symptoms of the infectious disease, and initial onset of the symptoms. If a medical facility was included in the patient’s route, quarantine of the medical facility was conducted.

2. GPS
Consistency in the recall of the route of the patients identified through interview was evaluated. Additionally, identification of the routes that the patient could not remember was also possible. However, another person’s information can be misunderstood as the patient’s information if the phone is not owned by or carried by the patient. GPS uses cellular phone networks, therefore there are limitations in identifying the exact locations of a patient’s route.

3. Credit card transaction log
Credit card transaction logs were used to assess the consistency in the route of the patient identified through interview, and the scope of contacts was assessed by specifying the locations visited. However, if the patient did not use a credit card under their name or if another person used the patient’s card, the information may be misinterpreted. Thus, rechecking the contents of the credit card log was necessary, and instances of not being able to use the information at the appropriate time may occur.

4. CCTV
By checking the video footage of the location of a patient’s path, CCTV provided help to identify the details of each situation. For example, CCTV was used to evaluate the level of exposure risk by identifying whether the patient wore masks, or had respiratory symptoms such as a cough. The limitations of using CCTV were the lengthy time required to check the CCTV, and the accuracy of patient identification if the CCTV was not inside the facility or the patient was in a blind spot of the camera.