*3.1. Survey Participants*

A total of 1716 individuals responded to the survey, of whom 1130 (65.9%) were COVID-19-confirmed patients and 586 (34.1%) were quarantined persons. Of the total participants, 600 (35%) were male and 1116 (65%) were female. The mean age was 35.8 years. By age group, 804 (46.9%) were under 29 years of age, 297 (17.3%) were 30–39, 264 (15.4%) were 40–49, 246 (14.3) were 50–59, and 105 (6.1%) were 60 years or older. A total of 471 (27.4%) participants recently entered South Korea from abroad in 2020. Of those, 33 had confirmed cases of COVID-19 and 438 were quarantined. Thus, it was found that approximately one out of every four quarantined persons was a recent traveler from abroad. A total of 417 (24.3%) participants had received a flu vaccine after October 2019. Regarding self-reported health status at the time of the study, 1045 (60.9%) participants answered "good", 529 (30.8%) responded "fair", and 142 (8.3%) answered "poor" (Table 2).


**Table 2.** Characteristics of survey participants \*.

\* Mean age (standard deviation) was 36.4 (13.4) for confirmed patients and 34.8 (13.0) for quarantined persons.

#### *3.2. COVID-19 Infection Symptoms*

With respect to COVID-19-related symptoms in confirmed patients, 834 (73.8%) were symptomatic and 296 (26.2%) were asymptomatic. Of the symptomatic cases, 588 (78.5%) were female and 246 (64.6%) were male, showing that the proportion of symptomatic cases was higher in women than in men (*p* < 0.001). However, the proportion did not vary according to age groups.

Of the individual COVID-19 symptoms, the most common was loss of smell (38.3%), followed by loss of taste (36.5%), cough (32.7%), muscle aches (31.3%), fever (28.4%), headache (27.6%), phlegm (26.6%), sore throat (24.4%), diarrhea (22.7%), chills (21.9%), difficulty breathing (10.0%), indigestion (9.2%), and nausea (6.8%) (Table 3).

#### *3.3. Precautionary Behavior Practices for Two Weeks before Isolation/Quarantine*

The analysis of the scores for precautionary behavior practice, for two weeks before isolation/quarantine in patients and quarantined persons, showed that the item regarding hand washing, "I always washed my hands after going to the bathroom", scored the highest in both patients and quarantined persons, with mean scores of 4.3 and 4.66, respectively. In comparison, the frequency of practice was lower for the item "I washed my hands (or used hand sanitizer) if I thought that my hands might have been contaminated because I shook hands, touched the mask, or held a doorknob", with mean scores for 3.45 in patients and 4.19 for quarantined persons. Moreover, among the items concerning correct maskwearing, "I always wore a mask during hospital visit" showed the highest practice level with mean scores of 4.12 for confirmed persons and 4.54 for quarantined persons. Of the items concerning person-to-person contact, "I avoided contact with others when I had symptoms like fever and a cough" showed the highest practice level, with mean scores of 4.12 for confirmed persons and 4.49 for quarantined persons. Overall, the precautionary behavior practice level was higher in quarantined persons than confirmed persons for all items (*p* < 0.001) (Table 4).


**Table 3.** Symptoms of infection in confirmed COVID-19 patients (*n* = 1130).

\* Including 765 duplicate respondents; n/a: Questionnaires are Not Applicable.

**Table 4.** Precautionary behavioral survey response results \*.


\* For a period of two weeks before confirmation/being quarantined.

The analysis conducted on the difference between genders in precautionary behavior practices showed that the mean scores for hand washing and cough etiquette were higher for women than men (*p* < 0.05); in regards to mask-wearing and person-to-person contact,

the results varied by item (Table 4). The age group difference was found in seven out of the total 14 items regarding precautionary behavior practices (*p* < 0.05). Of those, two items on person-to-person contact showed an opposite trend in comparison to the remaining items, which indicated higher scores as age increased (Supplementary Table S1).
