For treatment and control of E. vermicularis infection, it is recommended to take albendazole 400 mg or pyrantel pamoate 10 mg/kg in a single dose at 20-day interval at least 3 times [6]. However, it is quite difficult to manage and control the infection because of frequent and rapid reinfection and incomplete anthelmintic efficacy [2]. For this reason, it is recommended that all members of the family and classmate should be medicated at the same time. It is also important to keep the body clean and improve the environment through washing or disinfection of bedding and underwear [6].

In the Republic of Korea (= Korea), surveys of E. vermicularis infection have been continuously conducted, and it has been shown that its prevalence is decreasing gradually over time [1–4, 7–26]. However, most of the previous surveys were conducted under limited conditions, i.e., in local regions and targeting specific group during a short period of time [1–4, 7–26]. Thus, it is insufficient to understand the nationwide status of pinworm infection. In this study, we performed a 12-year nationwide survey to investigate the status of E. vermicularis infection among preschool children in Seoul, 4 large cities, and 9 provinces in Korea.

The survey was conducted once a year using the cello-tape perianal swab method during 2008–2019 targeting preschool children (aged 1–6) selected by 16 regional branches of the Korea Association of Health Promotion (KAHP). The total number of subjected preschool children during the 12 years was 638,354. The participants were randomly selected from children attending preschools (1–234 preschools each year in each regional branch) under permissions of parents, guardians, and/or director of the preschools which are located in Seoul, 4 large cities (Busan, Daegu, Incheon, and Ulsan), and 9 provinces (grouped into 5, namely, Gyeonggi-do, Gangwon-do, Chungcheongbuk-do, Chungcheongnam-do, Jeollabuk-do, Jeollanam-do, Gyeongsangbuk-do, and Gyeongsangnam-do). The study protocol was approved by the Ethics Committee for Health Research, the Korea Association of Health Promotion (IRB no. 130750-202009-HR-020). The perianal swab samples were prepared by the parent according to the instructions provided by the survey staff and collected from the parent or the guardian. The samples were transported to the laboratories of 16 branches of the Korea Association of Health Promotion (KAHP) and examined using a light microscope. The egg positive children were prescribed with albendazole 400 mg in a single dose 3 times at 20-day intervals. All statistical analyses were conducted using the Excel program (Microsoft, Redmond, Washington, USA), and P values of <0.05 were considered statistically significant.

According to the results, the egg positive rate of E. vermicularis decreased gradually within the period of investigation from 1.8% in 2008 and 2.0% in 2009 to 0.6% in 2019 (Table 1; Fig. 1A) (P<0.05). The egg positive rate was significantly higher in boys (0.7–5.0%, mean 1.8%) than in girls (0.5–2.8%, mean 1.3%) at any time except in 2017 (Fig. 1B) (P<0.05). The mean egg positive rate of E. vermicularis according to geographical regions during the 12 years was highest in Jeju-do, followed by Gyeonggi-do and Jeolla-do (including Jeollabuk-do and Jeollanam-do) and lowest in Gangwon-do, Seoul, and Chungcheong-do (Fig. 1C).

Enterobiasis is the most common human parasitic disease worldwide, including developed and developing countries [5,6,27–29]. In Korea, the survey of the prevalence of E. vermicularis has been continuously performed in most cases targeting preschool and primary school children in various regions [1–4,7–26] (Table 2). According to the reports, the prevalence of E. vermicularis has been decreasing over time in Korea. The prevalence in 2019 was 0.6%, considerably lower than other countries. Even in developed countries, the prevalence of E. vermicularis infection was quite high [27–29]. For example, in Berlin, Germany, the prevalence of E. vermicularis was 17.4% from 2007 to 2017 [27]. In the Sivas region of Turkey, the prevalence of E. vermicularis was 17.0% (365/3,569) co-infected with other parasites [28]. In northeastern Poland, the prevalence of E. vermicularis was 10.1% between 2013 and 2015 [29].

In our study, the prevalence of E. vermicularis infection tended to decrease over the surveyed period from 2008 to 2019. One of the reasons for the decrease seems to be the continued hygiene education and preventive chemotherapy. In fact, Kim and Yu [3] reported that it was sharply reduced in the experimental group trained for preventive education about E. vermicularis infection than in the control group after 3 months of treatment. In addition, the prevalence of E. vermicularis was relatively lower in orphanage children than in preschool and primary school children, because the orphanage children were regularly educated about personal healthcare and infectious diseases and received medication with anthelmintics [26]. According to Kim et al. [23], parent’s knowledge about enterobiasis was correlated with E. vermicularis infection of their children. For this reason, it was recommended that children and their parents be consistently provided with health education for their knowledge and prevention of enterobiasis [3,23]. The second reason infers from the decrease in the number of students in each class and preschool followed by the decrease in the frequency of contact and transmission rate. Actually, the average number of children per class of preschools reported by the Korean Educational Statistics Service was 26.3 in 2000, 21.0 in 2010, and 17.0 in 2019 [30]. Therefore, it is considered that the possibility of E. vermicularis infection would be increased proportionally to the number of students in a class.

In our study, the egg positive rate in 2011 was exceptionally high compared to other years (Fig. 1A). Two factors were suggested to be the reasons. One was the high prevalence in large cities (6.6%) and Jeolla-do (including Jeollabuk-do and Jeollanam-do) (7.2%) compared to lower prevalences in other areas (0–3.0%). The other was the much smaller number of examinees in 2011 (1,626 children) compared with other years (34,866–113,610 children each year). We consider that there may have an outbreak of E. vermicularis infection at that time in a few preschools subjected in this study. However, thereafter, sudden rising of the prevalence was not seen throughout the survey period.

In previous papers, the prevalence of E. vermicularis infection was higher in girls than in boys by 1980s, but the pattern of pinworm infection changed since the 1990s in Korea [15,17, 19–21,23–25]. Our study showed a significantly higher prevalence among boys than in girls, except in 2017 (P<0.05) (Fig. 1). The precise reason why boys are more highly infected with E. vermicularis than girls is unknown. However, it is considered that inadequate personal hygiene, particularly among boys, could be a risk factor for E. vermicularis infection [19].

Our study has a few strong points and a few weak points. One of the strong points is the large subjected population, from around 35,000 to 114,000 subjects each year except in 2011, totaling 638,354 children during the total 12 years. Another strong point is that our study covered nationwide localities, including Seoul, 4 large cities, and 9 provinces, thus, it was fairly good to see the national trend of E. vermicularis prevalence among preschool children. One of the weak points is that our study was not based on strictly randomized selection of participants in each branch of the Korea Association of Health Promotion. Another weak point is that the cello-tape perianal swabs were prepared by the parents of children, not by experienced technologists.

In conclusion, the prevalence of E. vermicularis seems to be decreasing in Korea when compared with previous results, but a low-grade infection is still maintained. Therefore, monitoring and control programs of enterobiasis should be implemented consistently in preschools in Korea. In addition, it is necessary to provide health education on enterobiasis against children as well as their parents.