Abstracts

Introduction

As originally described in the 3^rd edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-III), the somatization disorder (SD) is characterized by a wide variety of somatic symptoms affecting different organ systems. Previous studies define SD as the psychological mechanism whereby psychological distress is expressed in the form of physical symptoms. The most common of these symptoms are abdominal, back, and chest pain; dyspnea; headache; fatigue; cough; nervousness, and dizziness ¹1. Lipowski ZJ. Somatization: medicine's unsolved problem. Psychosomatics 1987; 28:294-7.^,22. Lipowski ZJ. Somatization: the concept and its clinical application. Am J Psychiatry 1988; 145:1358-68..

The SD, characterized by complaints of unexplained physical symptoms, is commonly present in children and adolescents in both primary and secondary care settings. This disorder significantly impacts children, as well as healthcare resources: such as in adults, there is a wide range of severity and handicaps resulting from SD ³3. Silber TJ, Pao M. Somatization disorders in children and adolescents. Pediatr Rev 2003; 24:255-61.. In recent decades, there has been a growing awareness of SD in childhood and adolescence in the world, with plentiful evidence explaining the high prevalence of SD in the adolescent population ³3. Silber TJ, Pao M. Somatization disorders in children and adolescents. Pediatr Rev 2003; 24:255-61.^,44. Ruchkin V, Schwab-Stone M. A longitudinal study of somatic complaints in urban adolescents: the role of internalizing psychopathology and somatic anxiety. J Youth Adolesc 2014; 43:834-45.. More specifically, a general teenage population (aged 12-16 years) survey found that SD was present in 11% of girls and 4% of boys ⁵5. Silber TJ. Somatization disorders. Pediatr Rev 2011; 32:56-64.. However, in studies from some European countries, the reported prevalence of SD ranged from 0.1% to 0.8% in the general Western population ⁶6. Faravelli C, Salvatori S, Galassi F, Aiazzi L, Drei C, Cabras P. Epidemiology of somatoform disorders: a community survey in Florence. Soc Psychiatry Psychiatr Epidemiol 1997; 32:24-9.^,77. Lieb R, Pfister H, Mastaler M, Wittchen HU. Somatoform syndromes and disorders in a representative population sample of adolescents and young adults: prevalence, comorbidity and impairments. Acta Psychiatr Scand 2000; 101:194-208.. Furthermore, epidemiological studies of adolescents aged 13-18 years conducted in Oman and the Philippines found higher prevalence rates of SD compared with Western countries ⁸8. Viernes N, Zaidan ZA, Dorvlo AS, Kayano M, Yoishiuchi K, Kumano H, et al. Tendency toward deliberate food restriction, fear of fatness and somatic attribution in cross-cultural samples. Eat Behav 2007; 8:407-17..

In a literature review, we also found that younger females from specific ethnocultural groups, with certain family medical histories or who have endured childhood sexual abuse, substance abuse, anxiety and depressive disorders or traumatic events are at an increased risk for adolescent SD ³3. Silber TJ, Pao M. Somatization disorders in children and adolescents. Pediatr Rev 2003; 24:255-61.^,44. Ruchkin V, Schwab-Stone M. A longitudinal study of somatic complaints in urban adolescents: the role of internalizing psychopathology and somatic anxiety. J Youth Adolesc 2014; 43:834-45.. Another study demonstrates SD has a major impact on the functioning and quality of life and can often affect anyone in early life for sustained periods, thereby leading to many years of disease ⁹9. Kroenke K, Outcalt S, Krebs E, Bair MJ, Wu J, Chumbler N, et al. Association between anxiety, health-related quality of life and functional impairment in primary care patients with chronic pain. Gen Hosp Psychiatry 2013; 35:359-65.. Costello et al. ¹⁰10. Costello EJ, Egger H, Angold A. 10-year research update review: the epidemiology of child and adolescent psychiatric disorders: I. Methods and public health burden. J Am Acad Child Adolesc Psychiatry 2005; 44:972-86. assert that SD may result in significant social, economic, and health burdens in children and adolescents. As such, to reduce future SD cases, exploring potential SD impact factors - including modifiable ones -, is necessary.

Some studies suggest that young people show early signs before the onset of SD, such as somatization tendencies (ST) ⁸8. Viernes N, Zaidan ZA, Dorvlo AS, Kayano M, Yoishiuchi K, Kumano H, et al. Tendency toward deliberate food restriction, fear of fatness and somatic attribution in cross-cultural samples. Eat Behav 2007; 8:407-17.^,1111. Gardner RM, Morrell Jr. JA, Ostrowski TA. Somatization tendencies and ability to detect internal body cues. Percept Mot Skills 1990; 71:364-6.. A study by Zhou et al. ¹²12. Zhou X, Min S, Sun J, Kim SJ, Ahn JS, Peng Y, et al. Extending a structural model of somatization to South Koreans: cultural values, somatization tendency, and the presentation of depressive symptoms. J Affect Disord 2015; 176:151-4. explains that STs are the tendency to experience and communicate psychologic distress in the form of somatic symptoms - that is, in a somatic tendency mode -, widespread in both our own as in other cultures. As such, STs are not in any sense pathological nor constitutes a medical or psychiatric problem. Some of them are entirely subjective and may represent bodily metaphors with which the patient expresses emotional distresses or conflicts. What patients subjectively perceive as pain or some other somatic discomfort represents the experiential aspect ¹¹11. Gardner RM, Morrell Jr. JA, Ostrowski TA. Somatization tendencies and ability to detect internal body cues. Percept Mot Skills 1990; 71:364-6.. Other studies indicate that STs put individuals at risk for several adverse outcomes, including furthered SD, chronic pain, long-term sequelae, and a range of other mental health problems such as suicide, anxiety, and depression disorders ⁸8. Viernes N, Zaidan ZA, Dorvlo AS, Kayano M, Yoishiuchi K, Kumano H, et al. Tendency toward deliberate food restriction, fear of fatness and somatic attribution in cross-cultural samples. Eat Behav 2007; 8:407-17.^,1313. Vargas-Prada S, Martínez JM, Coggon D, Delclos G, Benavides FG, Serra C. Health beliefs, low mood, and somatizing tendency: contribution to incidence and persistence of musculoskeletal pain with and without reported disability. Scand J Work Environ Health 2013; 39:589-98.^,1414. McCall-Hosenfeld JS, Winter M, Heeren T, Liebschutz JM. The association of interpersonal trauma with somatic symptom severity in a primary care population with chronic pain: exploring the role of gender and the mental health sequelae of trauma. J Psychosom Res 2014; 77:196-204.. Several prior studies report that Korean depressives manifest more STs and fewer feelings of guilt and suicidal ideation when compared with Western patients ¹²12. Zhou X, Min S, Sun J, Kim SJ, Ahn JS, Peng Y, et al. Extending a structural model of somatization to South Koreans: cultural values, somatization tendency, and the presentation of depressive symptoms. J Affect Disord 2015; 176:151-4.^,1515. Yoo SK. The cultural impact on depression expression and attitudes toward seeking professional help: a comparative study of Americans and South Koreans. Asia Pacific Education Review 2001; 2:94-100..

The links between STs and adverse outcomes are thought to reflect early signs of SD overtime. Even so, there is little information about such association. For example, although the links between STs and adverse outcomes have been well documented ¹³13. Vargas-Prada S, Martínez JM, Coggon D, Delclos G, Benavides FG, Serra C. Health beliefs, low mood, and somatizing tendency: contribution to incidence and persistence of musculoskeletal pain with and without reported disability. Scand J Work Environ Health 2013; 39:589-98.^,1414. McCall-Hosenfeld JS, Winter M, Heeren T, Liebschutz JM. The association of interpersonal trauma with somatic symptom severity in a primary care population with chronic pain: exploring the role of gender and the mental health sequelae of trauma. J Psychosom Res 2014; 77:196-204.^,1515. Yoo SK. The cultural impact on depression expression and attitudes toward seeking professional help: a comparative study of Americans and South Koreans. Asia Pacific Education Review 2001; 2:94-100., no specific prevalence or risk estimates pertaining to adolescent STs are available. Additionally, there is scant research containing empirical investigations of environmental impact factors causing STs. The theoretical work concerning the ST pathological mechanisms is also scarce. In a stark contrast, SD risk factors have been extensively researched. To effectively decrease the risk and prevalence of adolescent SD, we investigated potential ST impact factors using large-scale epidemiological studies to develop effective interventions against STs.

The purpose of this study is to estimate the prevalence of STs in adolescents. In particular, we are interested in evaluating environmental impact factors associated with STs across three eastern Chinese provinces. For this purpose, we designed a multicenter cross-sectional study to discuss the prevalence of adolescent STs. In addition, we conducted a multicenter case-control study to ascertain the ST environmental impact factors in this population.

Subjects and methods

Sample size calculation

To calculate sample size, we used the following formula ¹⁶16. Daniel WW. Biostatistics: a foundation for analysis in the health sciences. 7th Ed. New York: John Wiley & Sons; 1999.:

,where n = sample size; Z = Z statistic for confidence level; P = expected prevalence or proportion (in proportion of 1; if 50%, p-value = 0.50); and d = precision (in proportion of 1; if 2%, d = 0.02). Multistage sampling methods require a larger sample size to achieve the same precision; therefore, the sample size calculated using the formula above was multiplied by the design effect deff.

Z statistic (Z) ¹⁶16. Daniel WW. Biostatistics: a foundation for analysis in the health sciences. 7th Ed. New York: John Wiley & Sons; 1999.: for a 95% confidence level, which is conventional, the Z-value is 1.96. In this study, the investigators present their results with 95% confidence intervals (95%CI) and deff = 3. In addition, considering the loss to follow-up (referring to students who were lost in the follow-up survey), student rejection rate, sampling error, and stratification factors, the final sample size was determined to be 12,960.

Study methods

This research was a multicenter school-based, cross-sectional study. The schools were selected using a random number table and a stratified cluster sampling method, from three School Health Surveillance System (SHSS) centers from three provinces (Anhui, Jiangsu, and Zhejiang) in China; in total, 24 schools were recruited. A sample of 540 students aged 13-18 years was randomly selected at each of the enrolled schools using a random number table and a stratified sampling method. For inclusion, adolescents had to be mainstream students (i.e. have no intellectual disability), aged 13-18 years, and able to converse in Chinese. They were excluded in cases of a reported history of psychosis or neurocognitive deficits, or if they received a secondary mental health service. Further details are available in Figure 1.

In this study, adolescent STs were assessed in a two-stage appraisal procedure. In the first stage, STs were screened by the somatic subscale of the Brief Symptom Inventory (BSI) ¹³13. Vargas-Prada S, Martínez JM, Coggon D, Delclos G, Benavides FG, Serra C. Health beliefs, low mood, and somatizing tendency: contribution to incidence and persistence of musculoskeletal pain with and without reported disability. Scand J Work Environ Health 2013; 39:589-98.^,1717. Derogatis LR, Melisaratos N. The Brief Symptom Inventory: an introductory report. Psychol Med 1983; 13:595-605.. In the second stage, individuals whose responses to the BSI suggested they might have STs were further assessed by three psychiatrists to obtain a final diagnosis. About 60 trained fieldworkers administered 2 questionnaires to subjects who were assessed as presenting STs; face-to-face assessments and investigations were conducted in each of the 3 SHSS centers by the fieldworkers. In addition, 6 trained fieldworkers were present in each of these centers to control the quality of the research process.

We also designed a school-based collaborative case-control study, in which each center used a common protocol and core questionnaire. For each ST case, 2 control individuals matching in age, gender, and residence area were randomly selected from the 3 SHSS centers using a random number table method. Then, 3 or 4 control individuals were randomly selected to compensate for non-response and to ensure balance in the number of cases and control individuals at each center. For consideration, the control individuals had to be mainstream students (i.e. had no intellectual disability or history of psychosis/neurocognitive deficits); have a somatic symptoms score (SSS) < 10; be from the same area and of the same sex and age as the corresponding student in the case group; and be mentally healthy. To ensure the consistency of inclusion and exclusion criteria, all control individuals were assessed by a psychiatrist. Trained fieldworkers evaluated the potential ST impact factors in case and control students using standardized assessment instruments, including the Family Environment Scale (FES), the Chinese Adaptation Scale for Adolescents (CASA), the Student-Teacher Relationship Scale (STRS), the Chinese version of the Peer Relationship Inventory (CPRI), and the Hospital Anxiety and Depression Scale (HADS).

Measures and procedure

Adolescent ST measurement

This study featured a two-stage appraisal procedure to identify adolescent STs. In the first stage, the STs were screened with the BSI somatic subscale ¹⁷17. Derogatis LR, Melisaratos N. The Brief Symptom Inventory: an introductory report. Psychol Med 1983; 13:595-605., which involved questions about the distress caused by faintness or dizziness, pain in the heart or chest, nausea or upset stomach, trouble breathing, hot or cold spells, numbness or tingling in parts of the body, and weakness in parts of the body within 7 days before the screening. The BSI is a broadly applied self-reporting somatic symptoms scale discussed by Likert as five-point counts ¹⁸18. Clason DL, Dormody TJ. Analyzing data measured by individual Likert-type items. J Agric Educ 1994; 35:31-5., where each symptom was scored 0-4, depending on the distress it caused, yielding a total score of 0-28. The SSS were low (0-9), medium (10-19), and high (20-28) ¹⁷17. Derogatis LR, Melisaratos N. The Brief Symptom Inventory: an introductory report. Psychol Med 1983; 13:595-605.. Sample’s internal consistency was 0.84 (Cronbach’s alpha).

Individuals whose responses to the BSI suggested they might have STs (i.e. a medium or high SSS [≥ 10]) were further assessed by three psychiatrists (including two chief physicians and a senior attending doctor) to obtain a final diagnosis, as follows. First, aimed at improving the diagnostic consistency and accuracy of the three psychiatrists, they carefully reviewed the SD diagnostic criteria, as well as related studies on STs. Next, the psychiatrists excluded all patients with SD and other mental or personality disorders using the DSM and the Chinese classification of mental disorders. Then, they independently estimated STs in participants using a semi-structured questionnaire including demographic characteristics and somatization personality (SP) traits ¹⁹19. Villanueva Badenes L, Prado-Gascó V, González Barrón R. Emotion awareness, mood and personality as predictors of somatic complaints in children and adults. Psicothema 2016; 28:383-8.^,2020. Zijlema WL, Morley DW, Stolk RP, Rosmalen JG. Noise and somatic symptoms: a role for personality traits? Int J Hyg Environ Health 2015; 218:543-9.^,2121. De Gucht V, Fischler B, Heiser W. Job stress, personality, and psychological distress as determinants of somatization and functional somatic syndromes in a population of nurses. Stress Health 2003; 19:195-204.. To ensure the consistency of the different psychiatrists’ assessments, they utilized a mutual evaluation form; therefore, adolescent STs were only confirmed when consistently diagnosed by all three psychiatrists.

During such evaluation, the psychiatrists were primarily responsible for the ST diagnosis and differential diagnosis. The STs were noted if a subject had (a) a medium or high SSS (≥ 10); (b) SP traits (i.e. neuroticism, vulnerability to stress, and histrionic behavior) ¹⁹19. Villanueva Badenes L, Prado-Gascó V, González Barrón R. Emotion awareness, mood and personality as predictors of somatic complaints in children and adults. Psicothema 2016; 28:383-8.^,2020. Zijlema WL, Morley DW, Stolk RP, Rosmalen JG. Noise and somatic symptoms: a role for personality traits? Int J Hyg Environ Health 2015; 218:543-9.^,2121. De Gucht V, Fischler B, Heiser W. Job stress, personality, and psychological distress as determinants of somatization and functional somatic syndromes in a population of nurses. Stress Health 2003; 19:195-204.; (c) precluding organic diseases, SD, or other mental or personality disorders; (d) no history of psychosis or neurocognitive deficits; and (e) intact intellectual functioning (i.e. an intelligence quotient [IQ] > 70).

ST independently estimated by psychiatrists

A semi-structured questionnaire with 45 self-reported items (including demographic characteristics and SP traits) was designed to assess the participants’ STs. The questionnaire reliability was tested on 72 individuals in Suzhou, Jiangsu, whose STs are not included in this study. Responses were analyzed using Cronbach’s alpha, and the results revealed an internal consistency of 0.84 regarding demographic characteristics and of 0.81 in terms of SP traits, suggesting the validity of the designed questionnaire.

IQ measurement

To assess the participants’ IQs, we administered the Chinese revision of the Wechsler Adult Intelligence Scale for adolescents aged 17-18 years and of the Wechsler Intelligence Scale for Children for adolescents aged 13-16 years ²²22. Gong Y. The manual of Wechsler adult intelligence scale revised in China. Changsha: Hunan Medical University Press; 1992.. The IQ tests were age-standardized with a mean of 100 and a standard deviation of 15 in the general population ²³23. Breslau N, Paneth N, Lucia VC, Paneth-Pollak R. Maternal smoking during pregnancy and offspring IQ. Int J Epidemiol 2005; 34:1047-53.. Adolescents were individually assessed under the same standardized laboratory conditions, at all ages. In this study, intact intellectual functioning was assessed on a full scale. The fieldworkers were trained with a uniform standard, and all tests were scored by two independent testers.

Demographic characteristics measurement

A questionnaire was designed for assessing the demographic factors that contribute to STs. Such questionnaire included three main aspects: individual characteristics (gender, age, left-behind adolescents, and somatotype [referring to the overall outlook of the body to convey the totality of morphological features]), family factors (family income, family size, and superstitious beliefs [ranging from psychic powers to beliefs that are not attributable to scientific or religious explanations, such as supernatural, paranormal, or otherwise magical beliefs]), family medical history (i.e. a history of psychosis or neurocognitive diseases), and school characteristics (boarding school, administration model, and class size).

Social adjustment status measurement

The CASA is comprised of three factors: emotional adaptation (6 items), social adaptation (6 items), and study and life adaptation (5 items) ²⁴24. Zhang YB. The current situation and relationship of self-cognition, self-evaluation and adaptation of Chinese junior high school students. Beijing: Tsinghua University; 2008.. Related research suggests the CASA has high reliability and validity, with a 0.80 Cronbach’s alpha ²⁴24. Zhang YB. The current situation and relationship of self-cognition, self-evaluation and adaptation of Chinese junior high school students. Beijing: Tsinghua University; 2008.^,2525. Zhang DJ, Jiang Q. A report on construction of adaptation scale for adolescent. Studies of Psychology and Behavior 2006; 4:81-4.; hence, it was used as an effective tool to assess adolescents’ adaptation to social life. The adolescent adaptation was discussed using a four-point Likert scale for a total score of 17-68 points. In this sample, the internal consistency was 0.88.

School environment status measurement

Teacher-student relationship: the STRS is a 28-item self-report instrument designed to measure a teacher’s perception of their relationship with a given student ²⁶26. Pianta RC. The student-teacher relationship scale. Charlottesville: University of Virginia; 2001.. The Chinese version of the STRS (STRS-CV) is a version of the scale translated and revised by Qu ²⁷27. Qu ZY. The characteristics of class environment and its relationship with students' school adjustment in primary and middle school. Beijing: Beijing Normal University; 2002., based on Pianta’s STRS ²⁸28. Wei YH. A study on structure model and factors influencing the self-esteem development in children and adolescents. Beijing: Beijing Normal University; 1997.. It includes four domains: intimacy, conflict, support, and satisfaction. Good internal consistency and acceptable test-retest reliability (with a Cronbach alpha of 0.71-0.87) were assessed in the related research ²⁷27. Qu ZY. The characteristics of class environment and its relationship with students' school adjustment in primary and middle school. Beijing: Beijing Normal University; 2002.. The teacher-student relationship was tested using a five-point Likert scale for a total score of 23-115 points. In this study, the internal consistency was 0.87.

Peer relationship: the CPRI is a 20-item self-report instrument designed to assess an adolescent’s peer relationship. The CPRI was revised by Wei et al. ²⁸28. Wei YH. A study on structure model and factors influencing the self-esteem development in children and adolescents. Beijing: Beijing Normal University; 1997. based on the 13-item Missouri Peer Relations Inventory²⁹29. Borduin CM, Blaske DM, Cone L, Mann BJ, Hazelrigg M. Development and validation of a measure of adolescent peer relations: the Missouri Peer Relations Inventory. Columbia: Department of Psychological Sciences, University of Missouri; 1989., and measures three analytically derived dimensions of peer relations: social maturity, aggression, and independence. The scale has high reliability and validity (with a Cronbach’s alpha of 0.58-0.86) ²⁸28. Wei YH. A study on structure model and factors influencing the self-esteem development in children and adolescents. Beijing: Beijing Normal University; 1997.. Peer relationship was analyzed using a five-point Likert scale for a total score of 20-100 points. In this sample, the internal consistency was 0.86.

FES measurement

The FES is a 90-item self-report instrument used to measure relationships, personal growth, and system maintenance in the context of one’s family environment ³⁰30. Phillips MR, West CL, Shen Q, Zheng Y. Comparison of schizophrenic patients&apos; families and normal families in China, using Chinese versions of FACES-II and the family environment scales. Fam Process 1998; 37:95-106.. The Chinese version of the FES (FES-CV) was amended by Phillips et al. ³⁰30. Phillips MR, West CL, Shen Q, Zheng Y. Comparison of schizophrenic patients&apos; families and normal families in China, using Chinese versions of FACES-II and the family environment scales. Fam Process 1998; 37:95-106.. Previous studies found that 10 subscales of the FES-CV demonstrate moderate to excellent internal consistency (ranging from 0.63-0.75) and acceptable test-retest reliability (0.55-0.92) ³¹31. Hong JS, Tian J. Prevalence of anxiety and depression and their risk factors in Chinese cancer patients. Support Care Cancer 2014; 22:453-9.. The internal consistency of this instrument was 0.85.

Assessment of anxiety and depression

Anxiety and depression were evaluated using the HADS, which was specifically developed to detect anxiety and depression in patients with somatic conditions ³²32. Bjelland I, Dahl AA, Haug TT, Neckelmann D. The validity of the Hospital Anxiety and Depression Scale: an updated literature review. J Psychosom Res 2002; 52:69-77.. The HADS is divided into an anxiety subscale (HADS-A) and a depression subscale (HADS-D), both of which containing seven items scored 0-3, leading to a possible maximum score of 21. Scores < 8 indicate no clinical distress, scores 8-10 point out possible psychiatric morbidity, and scores ≥ 11 suggest probable pathologic levels of distress ³²32. Bjelland I, Dahl AA, Haug TT, Neckelmann D. The validity of the Hospital Anxiety and Depression Scale: an updated literature review. J Psychosom Res 2002; 52:69-77.. Good internal consistency and acceptable reliability were demonstrated for the Chinese version of the HADS (with Cronbach’s alphas of 0.81 for anxiety and 0.83 for depression) ³¹31. Hong JS, Tian J. Prevalence of anxiety and depression and their risk factors in Chinese cancer patients. Support Care Cancer 2014; 22:453-9.. In this sample, the internal consistency was 0.84.

Statistical analysis

All data were entered twice, verified, and de-identified in the EpiData open-source database, version 3.1 (http://www.epidata.dk/). Data were analyzed using R version 3.4.2 (http://www.r-project.org). Missing data imputation was conducted separately for each center, leading to three imputed datasets.

We used descriptive statistics to calculate the frequencies and percentages of the categorical variables as well as the mean ± standard deviation of the normally distributed continuous variables. The matched odds ratio (mOR), the adjusted mOR (amOR), and a 95% CI were used to measure the associations between impact factors and adolescent STs.

Univariate analyses were used to separately select all the covariates that were potentially associated with STs, to enter them into multiple regression models at a 0.05 significance level. We used three different analysis methods depending on the number and variety of variables: Independent t-tests were used for continuous variables with a normal distribution; Bartlett’s one-factor variance test was used for three or more variables with a normal distribution and variance homogeneity; Pearson’s chi-square test was used for categorical independent variables and to identify equilibrium between case and control students.

A conditional multiple logistic regression model was used to evaluate whether the covariates were associated with STs. A subsequent procedure was used to further select the covariates that were associated with ST at a significance level of p > 0.05, for removal, and a significance level of p < 0.05, for reentry. The final model was selected according to the minimum statistics of the Akaike information criterion. Hypothesis testing was conducted using a two-sided test with an alpha value of 0.05 to indicate statistical significance.

Results

Baseline subject characteristics

Refusal and loss-to-follow-up rates were 7.7% (994/12,960) and 4.7% (605/12,960), respectively, in the cross-sectional study. Overall, 11,361 questionnaires were completed at 24 schools. After removing questionnaires with incomplete data in any of the study’s dependent variables (n = 208, accounting for 1.8%), 11,153 participants were retained for subsequent analyses.

The overall positive ST rate among the eastern Chinese adolescents was 12.1% (95%CI: 11.5-12.7) at 13.8% (95%CI: 12.9-14.8) for females, and 10.3% (95%CI: 9.5-11.1) for males. The SSS (t = 6.37, p < 0.001) and positive ST rate (chi-square = 33.21, p < 0.001) in females were higher than in males. Remarkably, when comparing adolescents aged 13-18 years, the SSS and positive ST rate for the 18-year-old group were significantly higher than in other age groups (F = 32.84, p < 0.001; chi-square = 16.51, p = 0.006, respectively). In junior high school students (aged 13-15 years), grade 3 (aged 15 years) students’ SSS was higher than grade 1 or grade 2 students (F = 24.03, p < 0.001). Adolescents from rural areas had significantly higher SSS (t = 13.91, p < 0.001) and positive ST rates (chi-square = 7.78, p = 0.005) compared with adolescents from urban areas. The remaining two baseline characteristics, including nationality and sampling area, did not significantly relate to the SSS or positive ST rate in adolescents (p > 0.05) (Table 1).

Association between environmental impact factors and STs in eastern Chinese adolescents

We enrolled a total of 1,226 ST cases and 2,467 control individuals in our multicenter, case-control study. Refusal and loss-to-follow-up rates were 2% (26/1,300) and 3.7% (48/1,300) in the case group, and 1.8% (47/2,600) and 3.3% (86/2,600) in the control group, respectively. Case and control subjects were matched by age, gender, and residence area (1:2). Statistical differences in baseline characteristics, including age, gender, and nationality, were not found in the multicenter case-control study (p > 0.05). Therefore, this study was balanced.

Tables 2 and 3 summarize results of univariate analyses of the association between potential covariates and STs. About 21 of the 37 covariates tested were significantly associated with STs (p < 0.05), being the most significant: (a) demographic characteristics including family income, left-behind adolescents, family medical history, and superstitious beliefs; (b) social adjustment characteristics in terms of emotional adaptation; (c) teacher-student relationships, including intimacy, support, and conflict; (d) peer relationships for social emotion; e) family environment characteristics, including cohesion, conflict, and independence; and (f) psychological factors according to the HADS-A and HADS-D scores. The remaining 16 covariates (including parent education levels and occupations, environmental pollution, class staff, number of family members, social adaptation, study and life adaptation, teacher-student satisfaction, peers’ interpersonal interaction and harmony, family expressiveness and organization, family intellectual-cultural orientation, and family activity-recreational orientation) did not significantly relate to ST risk (p > 0.05) (Tables 2 and 3).

To further explore the possible associations between STs and impact factors, a conditional multiple regression analysis was performed, showing that family medical history, HADS-A and HADS-D scores, superstitious beliefs, left-behind adolescents, teacher-student support, family conflict, and family independence and achievement orientation were significantly linked to STs in adolescents (Table 4). The models also indicated that, out of all independent variables, family medical history was the strongest ST impact factor (amOR = 3.02, 95%CI: 1.88-5.76, p < 0.001) (Table 4).

Discussion

The prevalence of ST and SSS in adolescents

This is the first study to investigate and prove the prevalence of STs within a large sample of Chinese adolescents. Adolescent STs may become a serious public health problem in East China. Kihlstrom et al. ³³33. Kihlstrom JF, Glisky ML, Angiulo MJ. Dissociative tendencies and dissociative disorders. J Abnorm Psychol 1994; 103:117-24. report that the prevalence of dissociative tendencies in adolescents lies between 10% and 19%; results similar to those of our study. Other results have likewise been found in some studies with depressive and anxiety tendencies ³⁴34. Saluja G, Iachan R, Scheidt PC, Overpeck MD, Sun W, Giedd JN. Prevalence of and risk factors for depressive symptoms among young adolescents. Arch Pediatr Adolesc Med 2004; 158:760-5.^,3535. Lewinsohn PM, Gotlib IH, Lewinsohn M, Seeley JR, Allen NB. Gender differences in anxiety disorders and anxiety symptoms in adolescents. J Abnorm Psychol 1998; 107:109-17.. Our results indicate that, for preventing SD, STs and other mental disorders in adolescents, intervention strategies should be implemented.

As reported in our study, differences of adolescent gender, age, and dwelling area emerged in the SSS and positive ST rate of teenagers. Adolescent ST seems to affect more females than males, and a similar phenomenon appears in SD rates ³⁶36. Milani RM, Parrott AC, Turner JJ, Fox HC. Gender differences in self-reported anxiety, depression, and somatization among ecstasy/MDMA polydrug users, alcohol/tobacco users, and nondrug users. Addict Behav 2004; 29:965-71.. The reason for such gender discrepancy might be related to differences in emotional development during adolescence. We found the SSS and positive ST rate in adolescents aged 18 years old (grade 3 senior high school students) were significantly higher than in other age groups. In addition, the SSS of grade 3 junior high school students is higher than grades 1 or 2. Compas et al. ³⁷37. Compas BE, Connor-Smith JK, Saltzman H, Thomsen AH, Wadsworth ME. Coping with stress during childhood and adolescence: problems, progress, and potential in theory and research. Psychol Bull 2001; 127:87-127. suggest that successful adaptation to stress includes the ways in which individuals manage their emotions and think constructively, as well as how they act in social and nonsocial environments so as to alter or decrease stress levels. In contrast, failed adaptation to stress probably results in psychological problems. However, some adolescents aged 15-18 years most likely cannot effectively decrease sources of severe stress featured in this study. Thus, the prevalence of STs is higher in this population.

Another reason for the high prevalence of STs might be that there is a serious shortage of mental health education in schools. Evidence exists that, compared with adolescents at other levels of urbanization, rural adolescents fare worse on many indicators of mental health ³⁸38. Srinath S, Girimaji SC, Gururaj G, Seshadri S, Subbakrishna DK, Bhola P, et al. Epidemiological study of child & adolescent psychiatric disorders in urban & rural areas of Bangalore, India. Indian J Med Res 2005; 122:67-79.. Our study also found that adolescents in rural areas had significantly higher SSS and ST prevalence than in urban areas. As before, we suggest sex-specific, age-specific, and area-specific intervention programs should be considered to prevent STs in adolescents.

The environmental impact factors of adolescent STs

To our best knowledge, this is the first study to examine the associations between adolescent STs and a broad range of potential impact factors using a large population sample. In this study, family medical history, HADS-A and HADS-D scores, superstitious beliefs, left-behind adolescents, teacher-student support, family conflict, and family independence and achievement orientation contributed to the STs impact. It is worth noting that family medical history, HADS-A and HADS-D scores, superstitious beliefs, and family conflicts are significantly associated with STs. Our study implicates that bio-genetic, psychological, and family factors are the key impact factors in adolescents with STs. As reported in a recent study, possible genetic and environmental factors contribute to somatic symptoms in children and adolescents ³⁹39. Tøt-Strate S, Dehlholm-Lambertsen G, Lassen K, Rask CU. Clinical features of functional somatic symptoms in children and referral patterns to child and adolescent mental health services. Acta Paediatr 2016; 105:514-21.; a result which appears to be consistent with our study. Previous studies also state an association between SD and depression or anxiety disorders ⁷7. Lieb R, Pfister H, Mastaler M, Wittchen HU. Somatoform syndromes and disorders in a representative population sample of adolescents and young adults: prevalence, comorbidity and impairments. Acta Psychiatr Scand 2000; 101:194-208.. Similarly, exposure to depressive or anxiety symptoms was a risk factor for adolescent STs in our study. Why are depression and anxiety patients more likely to suffer from STs in adolescence? Such results may be due to the fact these patients likely experience more medical testing, days away from home and school, and also family financial burden compared with mentally healthy adolescents who are still in school. Moreover, previous work with patient samples highlights that frequent and recurrent somatic symptoms in children predict a substantially increased risk for emotional distress disorders (such as depression and anxiety) during young adulthood ⁷7. Lieb R, Pfister H, Mastaler M, Wittchen HU. Somatoform syndromes and disorders in a representative population sample of adolescents and young adults: prevalence, comorbidity and impairments. Acta Psychiatr Scand 2000; 101:194-208.. Therefore, the relationship between SD and depression or anxiety disorders are that of a psychiatric comorbidity.

Studies confirm that religious beliefs were found to significantly impact mental health ⁵5. Silber TJ. Somatization disorders. Pediatr Rev 2011; 32:56-64.. For instance, negative approaches to superstitious beliefs appear to be positively associated with anxiety disorders, as reported by James & Wells ⁴⁰40. James A, Wells A. Death beliefs, superstitious beliefs and health anxiety. Br J Clin Psychol 2002; 41:43-53.. This study shows that a significant association is found between STs and superstitious beliefs and, therefore, the existence of superstitious beliefs among adolescents should be emphasized as a high-risk ST indicator. As a result, Education and mental health professionals should observe high-risk adolescents with superstitious beliefs.

Our findings also indicate that left-behind adolescents are associated with STs. Parental migration may result in left-behind adolescents who are raised by other family members, such as grandparents ⁴¹41. Zhang N, Bécares L, Chandola T. Does the timing of parental migration matter for child growth? A life course study on left-behind children in rural China. BMC Public Health 2015; 15:966.. Any subsequent differences between parents and other caretakers in terms of family roles, education levels, and lifestyles may contribute to an unfavorable environment for the adolescents’ psychological development ⁴¹41. Zhang N, Bécares L, Chandola T. Does the timing of parental migration matter for child growth? A life course study on left-behind children in rural China. BMC Public Health 2015; 15:966..

In our study, teacher-student support is associated with a decreased risk of adolescent STs. Teacher support may be especially important for student engagement in school when adolescents are coping with stressful life events and their independent coping skills are developing ⁴²42. Reddy R, Rhodes JE, Mulhall P. The influence of teacher support on student adjustment in the middle school years: a latent growth curve study. Dev Psychopathol 2003; 15:119-38.. A secure relationship with a teacher may serve as a resource that permits young students to cope more effectively with novel academic and social demands. For example, Wang et al. ⁴³43. Wang MT, Brinkworth M, Eccles J. Moderating effects of teacher-student relationship in adolescent trajectories of emotional and behavioral adjustment. Dev Psychol 2013; 49:690-705. report that, among adolescents, emotional security with a teacher attenuates stress reactivity to negative events in the classroom. Other studies also show that the quality of teacher-student relationships in school has implications for the adolescents’ future academic, social, and behavioral outcomes ⁴¹41. Zhang N, Bécares L, Chandola T. Does the timing of parental migration matter for child growth? A life course study on left-behind children in rural China. BMC Public Health 2015; 15:966..

We found that interpersonal relationships in families of ST adolescents are characterized by more conflicts and less independence in comparison with families of non-ST adolescents; a negative family climate, for instance, may also affect the maintenance of mental disorders ⁴⁴44. Peris TS, Sugar CA, Bergman RL, Chang S, Langley A, Piacentini J. Family factors predict treatment outcome for pediatric obsessive-compulsive disorder. J Consult Clin Psychol 2012; 80:255-63.. This is most likely due to the complex and reciprocal influences of the overall family environment on the mental health development of adolescents. Conversely, a positive family climate may provide a “safe haven” for high-risk adolescents, support healthy development and optimal learning and living, and discourage the maladaptive behavior. Sheeber et al. ⁴⁵45. Sheeber L, Hops H, Alpert A, Davis B, Andrews J. Family support and conflict: prospective relations to adolescent depression. J Abnorm Child Psychol 1997; 25:333-44. assert that a stable family circumstance can play a key role in promoting the psychological health of adolescents. A related study suggests that family conflict has unique and direct associations with the emotional health of adolescents ⁴⁶46. Timmons AC, Margolin G. Family conflict, mood, and adolescents' daily school problems: Moderating roles of internalizing and externalizing symptoms. Child Dev 2015; 86:241-58.. It is well known that favorable family growth environments are conducive to adolescent mental health; hence, this study suggests that family achievement orientation is helpful in reducing adolescent STs. Given our and others’ studies, we believe mental therapies and family interventions are key to addressing the high ST prevalence among adolescents.

Most notably, our study suggests that family medical history is the strongest impact factor of adolescent STs. Early data found a highly significant association between family medical history and somatoform symptoms in children and adolescents ⁴⁷47. Schulte IE, Petermann F. Familial risk factors for the development of somatoform symptoms and disorders in children and adolescents: a systematic review. Child Psychiatry Hum Dev 2011; 42:569-83.; the World Health Organization also proved that each parent disorder examined, with the exception of suicide, was associated with an increased risk of offspring mental disorders ⁴⁸48. McLaughlin KA, Gadermann AM, Hwang I, Sampson NA, Al-Hamzawi A, Andrade LH, et al. Parent psychopathology and offspring mental disorders: results from the WHO World Mental Health Surveys. Br J Psychiatry 2012; 200:290-9.. Both of these sources are consistent with our findings.

Although the causes of both SD and STs are not very clear, the genetic transmission of mental disorders (meaning family medical history as an independent ST impact factor) is a likely mechanism. Whatever the pathogenesis of STs may be, a word of caution is justified given their adverse outcomes. As such, we suggest that early diagnosis and treatment of mental disorders in family members may effectively reduce the risk of adolescent STs and disease burdens, as well as supportive intervention for existing STs.

Limitations

Several limitations of this study shall be considered. Firstly, some of the data in our study were self-reported and, possibly, underreported; however, the confidential nature of our questionnaire may have significantly decreased underreporting. Second, because there is no standard approach for measuring STs, misclassification of some outcomes may have resulted in the underestimation of the associations between STs and impact factors; such underestimation may have been reduced by integrating both subjective and objective methods to measure ST. Additionally, only adolescents attending school were sampled; out-of-school adolescents were not included in this study. Thus, some caution should be exercised when generalizing the results from this study population to the entire adolescent population in China.

Acknowledgments

We would like to thank the participants and their guardians for kindly participating in this study, and the staff members of three School Health Surveillance System (SHSS) centers for their assistance in the field investigation for adolescents’ STs. This study was funded by the National Health and Family Planning Commission of the People’s Republic of China (grant n. 201202010) and Health and Family Planning Commission of Hangzhou Municipality (grant n. 2012A060).

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