Hand and Oral Hygiene Practices of South Korean Adolescents Before and During the COVID-19 Pandemic

Key Points Question How have the long-term trends of hand and oral hygiene among Korean adolescents changed since the COVID-19 outbreak? Findings This cross-sectional study of 963 644 Korean adolescents from 2008 to 2022 found an immediate improvement in hand hygiene behavior but a sustained decrease in both hand and oral hygiene practices during the pandemic. Female sex, older age, nonsmoking status, alcohol use, low household economic level, and poor school performance were considered risk factors for poor hand hygiene. Meaning This study encourages more effective promotion programs for hand and oral hygiene.


Introduction
Since the declaration of the COVID-19 pandemic by the World Health Organization (WHO), 1,2 further consideration has been given to hygiene practices to prevent exposure to pathogens via hands and saliva.Specifically, frequent handwashing was strongly recommended by health experts during the COVID-19 pandemic. 3The WHO provided a guideline that people should wash their hands with soap and running water before and after meals and after using the toilet. 4Because of the efforts made by government and health organizations to increase public interest in hand hygiene, people became aware of handwashing during the pandemic.
The American Dental Association (ADA) and WHO recommend brushing of teeth at least twice a day. 5,6A previous study 7 reported that the oral cavity may be a potential site for SARS-CoV-2 viral replication.Therefore, a few studies have explored the association of the COVID-19 pandemic with hand and oral hygiene (handwashing: Denmark [n = 72] 8 and France [modeling study] 9 ; toothbrushing: Nigeria [n = 996] 10 and multiple countries [n = 14 970]). 11These studies showed conflicting results and weak levels of evidence due to the limited small sample sizes, broad age ranges, restricted socioeconomic status, and short observation periods (mostly up to 2020).
There is a need to analyze long-term trends in handwashing and toothbrushing with representative samples and compare tendencies before and during the COVID-19 pandemic.Hence, this study aimed to investigate the 15-year trend in frequency of handwashing and toothbrushing using nationwide, large-scale data collected between 2008 and 2022.We examined whether the COVID-19 pandemic was associated with the frequency of handwashing and toothbrushing practices among South Korean adolescents.

Study Design
A total of 992 702 individuals participated in the survey during a period of 15 years.After excluding participants with missing data, the final sample size for this cross-sectional study was 963 644.We used general population-based data from these 963 644 respondents of the Korea Youth Risk Behavior Web-based Survey (KYRBS).This survey was conducted annually by the Korean Disease Control and Prevention Agency from January 1, 2008, to December 31, 2022, to assess health behaviors among Korean middle and high school students.This survey covered 98.2% of all Korean adolescents aged 12 to 18 years.It has also been established and reviewed by experts from the Ministry of Education and the Ministry of Health and Welfare.The target population of the survey consisted of both public and private schools in all South Korean provinces.Students were asked to complete a questionnaire in a computer laboratory in each school. 12Youth aged 12 to 18 years were recruited, and they voluntarily participated in the survey (mean response rate, 95%). 12,13The sampling strategy followed 3 steps.First, the population was stratified by 39 regions and level of school education.Second, proportional allocation methods were used for sampling distribution.
Third, school and class units were used for stratified cluster sampling, which minimized sampling errors.Weighting was also considered, allowing the sample to represent the entire population of Korean adolescents.The study protocol was approved by Kyung Hee University and the Korean Disease Control and Prevention Agency.All participants provided written informed consent.Our study adhered to the tenets of the Declaration of Helsinki. 14This study followed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guideline.

End Points
We investigated whether the COVID-19 pandemic changed hand and oral hygiene trends.Given that the first confirmed case of COVID-19 in South Korea was reported in January 2020, the years 2020, 2021, and 2022 were regarded as the COVID-19 pandemic era. 15The participants were asked to indicate whether they washed their hands with soap in the following circumstances: before meals at

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Adolescent Hygiene Practices Before and During the COVID-19 Pandemic school, after using the toilet at school, before meals at home, after using the toilet at home, and after coming in from outside.The response options for each circumstance were always, often, sometimes, and never.We recategorized the participants based on frequency of handwashing into 2 groups as follows: high (those whose response was always in every circumstance) and low.The question used to assess oral hygiene was, "How many times do you brush your teeth a day?"We followed the international guidelines set forth by the ADA and WHO for brushing teeth at least twice per day. 5,6,16 divided the respondents into 2 groups: those who brushed their teeth twice or more per day and those who did not.In addition, we compared the trends in hand and oral hygiene behaviors before and during the pandemic in each subgroup (by grade, sex, smoking status, current alcohol use, economic level, highest educational level of parents, and school performance).

Definitions of Covariates
The study variables included age, sex, grade (7-9 [middle school] and 10-12 [high school]), body mass index (BMI; calculated as weight in kilograms divided by height in meters squared using height, weight, sex, and age in reference to the 2017 Korean National Growth Charts for children and adolescents 17 ), smoking status (yes or no), current alcohol use (yes or no), parents' highest educational level (high school or lower, college or higher, or unknown), school performance (high, middle-high, middle, middle-low, or low), and household economic level (high, middle-high, middle, middle-low, or low). 18All variables are based on self-reported data. 12Individuals who smoked at least once within the past 30 days were considered current smokers, whereas those who had not smoked for the past 30 days were considered nonsmokers.We defined alcohol consumers as those who consumed alcohol at least 1 day within the past 30 days. 19

Statistical Analysis
We analyzed the KYRBS data to investigate the national trends in hand and oral hygiene behaviors during the past 15 years in the context of before and after the pandemic.Interrupted time series analysis was performed using an ordinary least-squares model (linear regression), logistic regression, and estimate of adjusted odds ratio (OR) to investigate immediate and sustained changes in hand and oral hygiene behaviors before and during the pandemic. 20We conducted sex and age standardization and adjustment for sex, grade, BMI, current alcohol use, current smoking status, highest educational level of parents, household economic level, and school performance.Furthermore, to compare the latest prepandemic period (2017-2019) with the pandemic period (2020-2022) more thoroughly, adjusted and weighted ORs were derived using binary logistic regression models. 21,22In addition, we examined the individual factors associated with hand and oral hygiene practices using binary logistic regression.Weighted ORs with 95% CIs were obtained after adjusting for the covariates.To evaluate the magnitude of risk change before and after the pandemic, the ratio of the ORs (95% CIs) were used.
All analyses were performed using SAS software, version 9.4 (SAS Institute Inc).A 2-sided P < .05 was considered statistically significant.

Results
Among the 963 644 adolescents who participated in the KYRBS from 2008 to 2022, a total of 495 697 (51.4%) were male and 467 947 (48.6%) female.The mean (SD) age of the study population  time (β = −0.018;95% CI, −0.022 to −0.015%; P < .001).Meanwhile, no immediate increase in oral hygiene practice was observed at the onset of the pandemic, with a rate of 0.1% (95% CI, −0.9% to 1.1%; P = .82).However, oral hygiene practice showed a sustained decrease (β = −0.018;95% CI, −0.020 to −0.016; P < .001)during the pandemic.We observed similar tendencies for immediate and sustained changes in the subgroups according to grade, sex, smoking, current alcohol use, highest educational level of parents, economic level, and school performance (eTable 1 in Supplement 1).
Figure 2 shows the adjusted and weighted ORs for the 2020-2022 vs 2017-2019 periods.
Elevated hand hygiene and decreased oral hygiene practices were observed during the pandemic compared with these practices in the prepandemic era.A similar tendency of changes in hand and oral hygiene before and during the pandemic was observed in the subgroup analysis.The trend in changes in hand and oral hygiene behaviors (prepandemic period [2008-2019] vs pandemic period [2020-2022]) is presented in eTables 2 and 3 in Supplement 1.

Study Findings
To the best of our knowledge, this is the first nationwide, long-term study to examine the 15-year trends in hand and oral hygiene using a data set of approximately 1 million South Korean adolescents.
In addition, this study also analyzed the factors associated with hand and oral hygiene.We found that the estimated proportion of adolescents with an optimal level of handwashing decreased before the COVID-19 pandemic.However, as the pandemic began, the proportion increased and then subsequently decreased.Older age, female sex, nonsmoking status, current alcohol use, low household economic level, and poor school performance were significant risk factors for poor hand hygiene during the pandemic.Meanwhile, the estimated proportion of adolescents with good oral hygiene decreased steadily during the past 15 years, and this decrease became more prominent during the pandemic.Boys; nonsmokers; those with middle, middle-low, and low school performance; those without high household economic level; and those with underweight, overweight, or obesity had a higher risk of poor oral hygiene.

Plausible Mechanism
This study indicated that the proportion of adolescents with good handwashing habits increased remarkably after the advent of COVID-19.The hands are critical vectors for transmitting infectious diseases. 23However, previous research supports the idea that handwashing was not considered a serious issue as it should have been. 24Throughout the pandemic, governments and health organizations emphasized handwashing education not only for those who worked in the health sector but also for the general public.Nationwide campaigns promoting handwashing appeared in the daily news, print ads, and billboards, which likely led to a noticeable growth in interest in hand hygiene.In addition, we found that various factors were associated with hand and oral hygiene practices.Despite exposure to the same campaigns, the degree of health awareness may vary, depending on individual circumstances and health literacy levels. 25 observed that the proportion of adolescents exceeding the recommended guidelines for toothbrushing decreased during the last 15 years, particularly during the pandemic.There are 2 possible explanations for this finding.First, during the pandemic, there were few campaigns related to toothbrushing, unlike for hand hygiene.Adolescents may have been more likely to neglect their oral health status than before, prioritizing the health of other organs that are directly linked to COVID-19.Studies on the association between toothbrushing and COVID-19 are scarce.Therefore, there is a lack of strong guidelines related to toothbrushing.Nonetheless, the oral cavity may contain pathogens that predispose individuals to viral infection, including COVID-19. 26Some studies have concluded that poor toothbrushing may increase the risk of COVID-19. 27,28Second, COVID-19associated psychological distress may change oral health-related behaviors. 11,29Psychological distress caused by depression, 30 loneliness, and suicidal ideation 31 is known to be associated with a lower frequency of toothbrushing.Because social isolation increased during the pandemic lockdown, emotional distress increased, which may have negatively affected toothbrushing frequency.

Comparison With Previous Studies
Few studies examined the association of the pandemic with hand or oral hygiene, and these studies were conducted in Nigeria, 10,11 Denmark, 8 and France. 9These studies showed conflicting results and a weak level of evidence because they were limited by small sample sizes, specific socioeconomic status, inappropriate statistical models, or short trends.Moreover, these studies conducted analyses over a wide age range.Importantly, we used a large population-based study with a data set that spanned 15 years to produce a representative sample and visualize long-term trends.Although another study conducted analyses over a wide range of ages, we focused specifically on adolescents because the formation of healthy hand and oral hygiene habits is important during adolescence and may subsequently be sustained into adulthood. 32

Policy Implications
Research has shown that although handwashing is a simple task for preventing the spread of infectious diseases, people tend to underestimate its importance. 33Because of the global endeavors to raise awareness about hand hygiene during the pandemic, there has been a significant increase in the frequency and quality of handwashing.We must ensure that this focus persists, even after the end of the pandemic.During the pandemic, campaigns using short videos on social media, poster advertisements, and mainstream television succeeded in promoting handwashing throughout the country.A previous study suggested that the promotion of hygiene behavior helps improve health outcomes and prevent the spread of infectious diseases. 34We should continue using platforms with high accessibility to reinforce awareness of hand hygiene practices.In addition, to maintain high hand hygiene adherence, the government should conduct training sessions on hand hygiene for adolescents, install handwashing stations with sanitizers in school, and organize awareness sessions for adolescents to help them understand the importance of preventing the spread of infections. 35like in hand hygiene, this study highlighted a decrease in the frequency of toothbrushing among adolescents during the pandemic.Although research supports the association between toothbrushing and COVID-19, there was a lack of oral hygiene promotion as a preventive approach to COVID-19. 36The oral cavity is known to be a crucial site for SARS-CoV-2 replication 7 ; however, the microbial pathway explaining its association has not been resolved yet. 379][40][41] According to an official guideline provided by the Korean Academy of Preventive Dentistry, it is recommended and safe to use toothpaste with antimicrobial properties 3 to 4 times a day for both children and adults. 40Stannous fluoride is known to disrupt bacterial glycolysis and, when combined with fluoride, acts to deter the buildup of dental plaque and calculus on the tooth's surface. 42Toothbrushing at least twice a day should be more strongly encouraged by dental professionals.We believe that oral hygiene should be regarded as an important approach for preventing SARS-CoV-2 infection.

Strengths and Limitations
This study has several strengths.This is the first study, to our knowledge, to explore the long-term trends of hand and oral hygiene behaviors among Korean adolescents and identify how the

was 15 .
01 (1.75) years.A total of 51.2% of the participants were in grades 7 to 9 (middle school) and 48.8% were in grades 10 to 12.The baseline characteristics of the adolescents are presented in the Table.

eTable 1 in
Supplement 1 and Figure 1 provide the age-and sex-standardized interrupted time series analyses of hand and oral hygiene practices among Korean adolescents from 2008 to 2022.An immediate increase of 73.3% (95% CI, 59.4% to 97.4%; P < .001) was observed in the overall hand hygiene practice at the outbreak of the COVID-19 pandemic; however, it gradually decreased over JAMA Network Open | Public Health Adolescent Hygiene Practices Before and During the COVID-19 Pandemic

Figure 1 .
Figure 1.Age-and Sex-Standardized Interrupted Time Series Analysis of Hand and Oral Hygiene Practices and the COVID-19 Pandemic Intervention Among Korean Adolescents, 2008-2022

Figure 3 .
Figure 3. Ratio of Odds Ratios (ORs) for the Association Between Hand and Oral Hygiene Practices and Sociodemographic Factors

SUPPLEMENT 1. eTable 1. Interrupted
Time Series Results for Change in Hand and Oral Hygiene Practices After Versus Before the COVID-19 Pandemic Among Korean Adolescents, 2008-2022 eTable 2. Adjusted and Weighted Estimation of Trend in Adolescent Hand Hygiene Practice in South Korea, 2008-2022 eTable 3. Adjusted and Weighted Estimation of Trend in Adolescent Oral Hygiene Practice in South Korea, 2008-2022 eTable 4. Adjusted and Weighted Logistic Regression Analysis for the Association Between Hand Hygiene Practice and Risk Factors eTable 5. Adjusted and Weighted Logistic Regression Analysis for the Association Between Oral Hygiene Practice and Risk Factors