This study identified space–time clusters of cases of adolescent suicide using DBSCAN based on Korean student suicide data from 2016 to 2020. As a result, 9.7% (n = 63) corresponded to the space–time suicide cluster, and each cluster consisted of 3–9 suicide events and suicides temporally occurring between 7 and 59 days and corresponded to the distances between suicide cases within the top three most concentrated clusters, ranging from 6 to 32 km spatially. The suicide cluster group had low economic status and fewer psychiatric disorders compared to the non-clustered group. To the best of our knowledge, this is the first study to use latitude and longitude for spatial analysis and exact suicide dates for temporal analysis in the clustering of adolescent suicides, and it uses narrower spatiotemporal units of analysis than previous studies using DBSCAN without pre-setting spatiotemporal parameters.

In this study, 9.7% of adolescent suicides were classified into spatiotemporal suicide clusters, which was a higher percentage than previously reported. This increase could be attributed to differences in the analytic methods. The current findings suggest that interrelated suicides may be more frequent than expected in adolescents [5]. However, this study statistically identified spatiotemporal suicide clusters but did not confirm that suicides within clusters were actually related to suicides. Suicides that occurred within similar time periods in similar locations could have been classified into this space–time suicide cluster, even if there was no real connection. Future research should include a detailed case study of the suicide cases in these clusters.

The mechanisms leading to suicide clusters include social transmission, particularly person-to-person transmission and the media [5, 6, 18]. In addition, clustered suicide occurs through perceptions that suicidal behavior is widespread and assortative, leading to susceptible young people being likely to socialize with at-risk peers, and the social cohesion of the peer group contributes to the spread of ideas and attitudes [5, 6]. The effect of suicide clusters on schools is usually profound, and the early identification of suicide clusters and initiation of appropriate interventions is critical for preventing subsequent suicides. This study suggests that once an adolescent died by suicide, close monitoring and intervention may be needed to prevent subsequent suicides for about 2 months.

Several features of the clustered adolescent suicides in this study were similar to the socioeconomic characteristics of previously identified clustered suicides. Previous studies have identified deprivation [31, 43], poverty [22, 23, 43,44,45], and geological isolation [25, 30, 46] as significant risk factors for clustered suicide. In this study, economic status was lower among the clustered suicides than the non-clustered suicides in both the chi-square test and logistic regression analysis, which mirrors the results of previous studies.

In previous studies, young men were more frequently included in the clustered suicide groups than were young women [24, 47, 48]. However, this finding has not been replicated in other population-based studies targeting young adults and adolescents [5, 11, 25]. Similarly, there was no difference in the gender ratio between clustered and non-clustered suicides in our study, the first to report the gender characteristics of clustered suicides in Korean adolescents. This could be due to differences in the analytical method (DBSCAN) used to identify suicide clusters between this study and previous studies. Furthermore, 654 suicides were included in the analysis, which is fewer than in previous studies; this could have potentially influenced the results. Hence, future studies that target a larger number of suicides over an extended period are needed.

Regression analysis revealed that the clustered suicide groups had fewer psychiatric disorders than the non-clustered suicide group. This differs from previous findings and suggests that psychiatric history is a risk factor for clustered suicides [6]. However, it should be noted that the assessment of psychiatric disorders among students who died by suicide was based on parental reports after suicide rather than the direct application of standardized diagnostic tools, thus potentially failing to adequately capture the frequency of psychiatric disorders. Even if the students had clinically diagnosed psychiatric disorders, they may not have visited hospitals because of negative perceptions associated with mental health or that parents did not accurately report due to concerns about potential disadvantages the students might face at school. Additionally, no statistically significant differences were observed regarding the presence of psychiatric disorders between the two groups in the chi-square test. Given the limited number of participants, further research is necessary to address these findings.

Another distinctive characteristic of clustered group was their low economic status, which is consistent with previous studies [18, 22, 23, 31, 43,44,45]. However, earlier studies have not clarified the relationship between socioeconomic status and suicide clustering. In some studies [22], low economic status has been suggested as a proxy for factors associated with the clustering of suicides, such as limited access to mental health treatment. Since limited information was collected from each participant, our study could not clearly explain the underlying mechanism. Considering the multidimensional risk factors of adolescent suicide [49], and the general social stigma against psychiatric disorders in South Korea [50], having a low economic status might also decrease help-seeking behavior for the early detection of mental health problems of clustered suicide adolescents in Korea.

Although differences in peer problems were a non-significant trend (p < 0.10) between the groups, the clustered suicide group reported more peer problems than the non-clustered group. When examining each case of clustered suicide, it is apparent that the students included in the clustered suicide did not exhibit considerable vulnerability to suicide on a personal level. Considering the other characteristics mentioned above, this finding may be because they grew up in economically disadvantaged households with vulnerable support systems, delayed their development of introspection and help-seeking behaviors, and lacked resilience, leading to their immersion in peer relationships.

In summary, by using DBSCAN to analyze clustered adolescent suicides in Korea, we found a higher rate (9.7%) than that reported in previous studies. Moreover, the temporal range for the clustered suicides identified was within 2 months. These suicides were characterized by lower economic status, which is consistent with previous studies [22, 23, 43,44,45]. Our study differs from previous studies in that we used a methodology that did not use a specific window, providing a basis for identifying the critical time and regions for subsequent adolescent suicide prevention.

This study has several limitations. First, suicide cases among adolescents used in our study only included those reported by schools; thus, out-of-school adolescents were excluded. Second, our study exclusively focused on Korean students who died by suicide over 5 years, resulting in a limited sample size. This is because our study was a secondary analysis of data collected during a limited period, 2016–2020, as part of a suicide prevention policy in Korea. Correspondingly, given the exclusive focus on Korean adolescents, the distinct attributes of suicide may be influenced by national and cultural contexts, impeding the generalization of this study’s outcomes to diverse international settings. Third, we defined clustering as involving a minimum of three suicides; thus, cases in which two consecutive suicides occurred in a spatiotemporal context similar to clustered suicides were not included. Fourth, we did not account for factors that could link adolescents who died by suicide, even when not in geographically similar spaces, such as the Internet or social network services. Therefore, clustered suicides among adolescents might not have been adequately identified. Finally, the geographic data employed in this study were derived from school addresses rather than the residential addresses of adolescents who died by suicide, consequently failing to accurately reflect the specific locations of suicide incidents. However, Korean students are assigned to schools through a system known as the school district [51], wherein the proximity of a student’s residence serves as the paramount criterion for school assignment. Therefore, the addresses of the schools utilized in our research can indirectly represent the actual places of residence, and this window is much narrower than the previous studies that used county-level data. Additionally, in the Korean context, the living environment and peer groups of adolescents are often organized on a school-based scale, thereby highlighting the significance of the findings of this study.