Prevalence and prognosis of schizophrenia in Jinuo people in China: A prospective 30-year follow-up study

Abstract

Background:

There are few studies investigating the influence of the development on mental health of minorities in China.

Aims:

To follow up the prevalence, natural course and prognosis of schizophrenia in Jinuo people, the last group to be recognized as a ‘national minority’ in China, every 10 years since 1979.

Methods:

From 1979 to 2009, 15%–19% of Jinuo residents were evaluated by random cluster sampling and followed up every 10 years using the Chinese version of the Composite International Diagnostic Interview (CIDI) as the screening tool and the International Classification of Diseases (ICD) as diagnostic criteria tool.

Results:

There were no significant differences for the lifetime prevalence and current prevalence of schizophrenia across the three decades. Neither were there any significant differences for the prognosis of schizophrenia; however, at least half the patients had deteriorated or had residual symptoms in the follow-up. PANSS symptoms were significantly different according to different illness duration.

Conclusions:

During the three decades, there was no increasing trend for schizophrenia prevalence in Jinuo society; however, the prognosis of schizophrenia was not optimistic. In the natural, untreated status, schizophrenia patients with an illness duration of more than 20 years had more serious symptoms.

Keywords

Schizophrenia prevalence follow-up study Jinuo people

Introduction

There is now very strong evidence that the incidence of schizophrenia and other psychoses is elevated (albeit to varying degrees) in many migrant and minority ethnic populations (Morgan, Charalambides, Hutchinson & Murray, 2010). The evidence provisionally suggests that these high rates are largely social in origin (Morgan et al., 2010). Recently, Van Os, Kenis and Rutten (2010) reviewed that although heritability is often emphasized in schizophrenia, onset is associated with environmental factors such as early life adversity, growing up in an urban environment, minority group position and cannabis use.

Regarding the prognosis of schizophrenia, much evidence shows better outcomes of patients taking medication. Lambert, De Marinis, Pfeil, Naber and Schreiner (2010) found that after treatment with risperidone long-acting injection, improved outcome occurred in 21% of patients, and predictors of this included baseline symptom severity, baseline functioning, country, schizophrenia type and early positive treatment course. Despite this evidence, little is known about the natural course and prognosis of schizophrenia, especially for those patients without medication in rural regions of China.

Since 1978, Chinese society has experienced rapid and dramatic socio-economic development, especially apparent in rapid technical modernization and urbanization. All Chinese people, those of the Han majority population as well as those of the more than 50 distinct Chinese ethnic ‘nationalities’, have been directly and indirectly impacted by these changes. According to the literature mentioned above, there is the hypothesis that the prevalence of mental disorders will increase in Chinese society, especially among ethnic nationalities. Recent data has shown the increasing prevalence of mood disorders, anxiety disorders, substance abuse disorders and psychotic disorders in four provinces of China (Phillips et al., 2009). However, research so far has lacked data about the prevalence, natural course and prognosis of schizophrenia in ethnic nationalities, particularly in longitudinal studies.

The Jinuo nationality is one of the minorities that is unique to Yunnan Province, which is famous for its multiple minorities in China, and was the last group to be recognized by the Chinese Central Government, in 1979, as a ‘national minority’. Now there are nearly 11,000 Jinuo people in total and almost all live in Jinuo Mountain in Xishuanbanna of Yunnan Province. Before the 1970s, Jinuo people had lived poorly in an isolated agricultural society. With the help of the Chinese government after that, Jinuo society moved directly from a low level of productivity with quite poor agricultural tools and at the mercy of ruthless natural forces, to the much richer life. During these developments, modernization and urbanization gradually affected the local people’s life. A modern way of life, culture and education have integrated into Jinuo society. Will these changes bring the Jinuo people mental problems as well as wealth? To look into this, a longitudinal study was carried out every 10 years from 1979 to follow up the mental health problems of Jinuo people (Li, Zhu & Wan, 1994; Li et al., 2008; Wan et al., 1981, 1982; Zhu, Li & Wan, 1994). This paper will present the three decades of follow-up results on schizophrenia.

Method

Subjects

Most of the Jinuo people live in 44 unincorporated villages in Jinuo Mountain. According to 2009 official census data, their population totals 10,610. Every 10 years we explored the 44 villages to screen schizophrenic patients using random cluster sampling. The total population in 1979 was 1,432 families and 8,682 individuals (4,303 male, 4,379 female); in 1989 it was 2,105 families and 10,403 individuals (5,372 male, 5,031 female); in 1999, 2,310 families and 10,398 individuals (5,485 male, 4,913 female); and in 2009, 2,578 families and 10,610 individuals (5,634 male, 4,976 female).

Methods

Instruments

Socio-demographic information

A number of socio-demographic variables were assessed, including gender, age, ethnicity, education level, occupational status, marital status and average annual income of family in the last year.

The International Classification of Diseases (ICD) (Slee, 1978; WHO, 1992). The 1979 ninth revision (ICD-9) was used for the classification of almost all diseases in China until the Ministry of Health announced the national unified use of ICD-10 in 2002. Therefore, ICD-10 was used as diagnosis criteria in the 2009 survey and ICD-9 was used in the earlier surveys.

Composite International Diagnostic Interview (CIDI) (Kessler & Üstün, 2004). The Chinese version of CIDI (Su, Zhang & Wang, 1993), provided by the Chinese Center for Disease Control and Prevention, was used as the screening tool and the diagnoses were made with the ICD criteria for schizophrenia. In the 2009 survey, CIDI 3.0 was used (Huang et al., 2010).

Positive and Negative Syndrome Scale (PANSS) (Kay, Opler & Fiszbein, 1987; Si et al., 2004). In 2009, the PANSS was used to evaluate all recruited schizophrenic patients for positive, negative and general symptoms.

Clinical Global Impressions Scale (CGI) (Guy, 1976). The CGI was developed for use in clinical trials sponsored by the National Institute of Mental Health to provide a brief, stand-alone assessment of the clinician’s view of the patient’s global functioning (Guy, 1976). Over the past 30 years, the CGI has been shown to correlate well with standard scales (Hamilton Rating Scale for Depression, Hamilton Rating Scale for Anxiety, Positive and Negative Syndrome Scale, Brief Psychiatric Rating Scale) across a wide range of psychiatric conditions (Bandelow, Baldwin, Dolberg, Andersen & Stein, 2006; Leucht & Engel, 2006; Leucht et al., 2005; Spielmans & McFall, 2006; Zaider, Heimberg, Fresco, Schneier & Liebowitz, 2003). In the present study, we used the Clinician Global Impression of Severity (CGI-S) and Clinician Global Impression of Improvement (CGI-I) to evaluate patients’ functioning. In the seven-point scale of CGI-S, a score of 1 was rated as normal. In the follow-up, a score of 2 indicated remission.

Sampling, follow-up and screening

The research undertaken in 1979 was the first survey, so it just screened the patients. After that, each survey included two parts: following up old patients and screening new-onset patients.

Randomized cluster sampling methods were used to identify subjects. In each household all Jinuo adults over 18 years of age who had resided in the villages for at least six months in the year prior to the interview were identified and one in each household was selected as the target subject using a random numbers table. In the surveys carried out in 1979, 1989 and 1999, more than 15% of residents in each village were randomly selected (Li, Zhu & Wan, 1994; Li et al., 2008; Wan et al., 1981, 1982; Zhu et al., 1994).

In 1979, 1989 and 1999, schizophrenic patients were diagnosed according to ICD-9. However, as the Ministry of Health announced in 2002 the national unified use of ICD-10, in 2009 all the patients identified in the first three studies were ‘blinded’ to re-diagnose them according to ICD-10. In addition, the PANSS scores and prognoses of these patients were also evaluated in 2009.

In 2009, 1,984 subjects were recruited from 44 villages, accounting for 19% of the total population. Of these, 1,047 (53%) were male and 937 (47%) were female, the mean age was 39.84 ± 15.61 years, and average years of education was 6.02 ± 3.41. All positive subjects and 5% of negative subjects who were screened by CIDI 3.0 were assigned to complete the face-to-face diagnostic assessment using the ICD-10 with three experienced psychiatrists. Multiple current (one-month) and lifetime diagnoses ranked according to clinical importance were recorded in this interview.

Quality control

The studies were carried out smoothly with the help of the local health bureau and village committees. During the surveys, doctors from the local hospital and guides from the villages assisted us in communicating with participants, and the local hospital also provided patient information for all 44 villages.

In each survey, all interviewers were carried out by the same researchers over three weeks. Diagnostic inter-rater agreement was 0.79.

During the study, interviewers were divided into three groups of two to four. Each group was supervised by an experienced psychiatrist. All questions were administered to subjects orally. Interviewers mainly spoke Mandarin during the interviews, which was adequate in half of the cases. In situations when communication was difficult, mutual translation between Mandarin and the local dialect was provided by a local guide or doctor. We hired one or two local guides for each group of interviewers to assist with gaining access to a household.

This study was approved by the ethics commission of the Second People’s Hospital of Yunnan Province and the First Affiliated Hospital of Kunming Medical University, Yunnan Province, China. Oral informed consent was obtained before the interviews.

Statistical methods

The data were analysed descriptively using analyses of frequency and means for sample demographic data and PANSS scores. Prevalence of schizophrenia was then estimated. χ² tests were used to compare prevalence and different prognosis rates over the 30 years. Analyses of covariance (ANCOVA) and t-tests were used to compare the PANSS scores among patients with different illness duration. Statistical significance was determined with an α level of 0.05. All calculations were carried out using SPSS 15.0. The statistic power of this sample was calculated by the GPower 3.1.2 program (Faul, Erdfelder, Buchner & Lang, 2009; Faul, Erdfelder, Lang & Buchner, 2007).

Results

Prevalence and prognosis of schizophrenia from 1979 to 2009

Table 1 shows the prevalence and prognosis of schizophrenia. There were no significant differences in the lifetime and current prevalence across the three decades.

Table 1.

Prevalence and prognosis of schizophrenia from 1979 to 2009.

	Number interviewed	Lifetime prevalence			Adjusted lifetime prevalence (‰)^**	Current prevalence			Adjusted current Prevalence (‰)^**	Estimated prognosis n (%)^**
	Number interviewed	NP	ENP	Prevalence (‰)	Adjusted lifetime prevalence (‰)^**	NP	ENP	Prevalence (‰)	Adjusted current Prevalence (‰)^**	D1	D2	R
1979	M: 886 F: 51	M: 4 F: 3	M: 18 F: 13	4.03	M: 4.62 F: 3.55 T: 4.09	M: 4 F: 1	M: 18 F: 4	2.42	M: 4.62 F: 1.09 T: 2.91
1989	M: 891F: 928	M: 4F: 3	M: 17F: 12	3.85	M: 4.36F: 3.27T: 3.84	M: 4F: 1	M: 17F: 4	2.40	M: 4.36F: 1.09T: 2.78	9 (29.03)	18 (58.06)	4 (12.90)
1999	M: 1071F: 950	M: 4F: 4	M: 15F: 15	3.96	M: 3.85F: 4.09T: 3.97	M: 4F: 2	M: 15F: 8	2.91	M: 3.85F: 2.18 T: 3.04	7 (24.69)	18 (60.51)	5 (14.80)
2009	M: 1047F: 937	M: 5F: 3	M: 19F: 8	4.03	M: 4.88F: 3.27T: 4.09	M: 4F: 1	M: 15F: 4	2.5	M: 3.85F: 1.09T: 2.51	5 (18.87)	17 (62.26)	5 (18.87)

NP = number patients; ENP = estimated number patients; D2 = deteriorated or residual; R = remission; F = female; M = male; D1 = death; T = total.

p > .05

In the 2009 study, of the 1,984 subjects recruited, only seven were schizophrenic patients, with a mean age 49.53 ± 14.35 years old, which led to the total adjusted lifetime prevalence of schizophrenia being 4.09‰ (Table 1). Five of these patients were male, with a lifetime prevalence of 4.88‰, whereas the lifetime prevalence for females was significantly lower at 3.27‰ (χ² = 9.78, p < .01).

Among the seven schizophrenic patients, five were still in illness status in 2009 (total PANSS > 60), with a mean age of 50.65 ± 14.71 years. The current prevalence of schizophrenia for males (3.85‰) was significantly higher than that for females (1.09‰) (χ² = 9.56, p < .01). The total adjusted current prevalence was 2.51‰ (Table 1).

Table 1 also showed that there were no significant differences for the prognosis of schizophrenia patients in 1989, 1999 and 2009.

Prevalence of psychotic symptoms (from CIDI) from 1999 to 2009

As shown in Table 2, there were no significant differences for either negative or positive symptoms across the two surveys, even after adjusting for demographics.

Table 2.

Prevalence of negative and positive psychotic symptoms from 1999 to 2009.

	Number interviewed	Prevalence of negative symptoms n (%)	Odds ratio (95% CI)	Prevalence of positive symptoms n (%)	Odds ratio (95% CI)
1999	2,021	26 (1.29)	1^a	324 (16)	1^a
2009	1,984	25 (1.26)	1.48 (0.87–2.17)	316 (15.9)	1.34 (0.77–1.94)
Odds ratio linear trend^b			1.16 (0.69–1.34)		1.21 (0.87–1.49)
Adjusted for demographics^c			1.11 (0.60–1.28)		1.15 (0.69–1.41)

Reference category.

The summary increase in risk with one unit change in each survey.

Age, gender, marital status, unemployment, educational level.

Status of schizophrenic patients

PANSS symptoms at the 2009 follow-up

From 1979 to 2009, 30 schizophrenic patients were identified in total. By 2009, two had died from suicide, five had died from heart attack and accident, and two were missing. This left 21 patients that could be contacted for the 2009 survey. Among these, only one had received perphenazine treatment for half a year. Among the 20 untreated patients, 10 had a mean illness duration of more than 20 years, six had a duration of 10–20 years, two of less than 10 years, and two of four to six months.

Table 3 shows the PANSS symptoms of the 20 untreated patients. The post hoc test showed that the patients whose illness duration was less than one year had the highest positive sub-score (p < .001), and those whose illness duration was more than 20 years had the lowest (p < .001). For the negative sub-score, the patients whose illness duration was less than one year scored lowest (p < .001), and those with a duration of more than 20 years scored highest (p < .001). For the general psychopathological sub-score, patients with an illness duration of more than 10–20 years scored highest (p < .001), and those with a duration of less than one year scored lowest (p < .001). Finally, patients with an illness duration of more than 20 years had the highest total score (p < .001), while those with a duration of less than one year had the lowest (p < .001).

Table 3.

PANSS symptoms of the 20 untreated schizophrenic patients in 2009.

	≥ 20 years duration (n = 10)	10–20 years duration (n = 6)	< 10 years duration (n = 2)	< one year duration (n = 2)	F	p
Positive sub-score	16.4	16.9	16.8	17.4	28.922	< .001
Negative sub-score	19.7	19.2	19.1	18.3	167.704	< .001
General psychopathological sub-score	34.3	34.5	33.7	32.0	136.897	< .001
Total score	69.7	69.3	68.4	66.5	196.063	< .001

When α was set under 0.05, according to the prevalence of the 1999 study, the power analysis showed that the statistical power was 71.4% for the 2009 study.

Discussion

The Jinuo nationality is an ethnic group that is unique to Yunnan, and is one of the smallest ethnic groups in China. They seldom intermarry with other ethnic groups. From 1999 to 2009, 510 persons surveyed had married, but less than 10% had intermarried with other ethnics. So, to a large extent, the Jinuo people preserve their original lifestyle and habits. However, on the other hand, the course of modernization is now enriching their life. Although lack of relevant data means that it is not known whether the Jinuo Mountain is already urbanized, the demographics (average annual family income) have already demonstrated that the whole ethnic group may have become more modern and more affluent. Following up the change in the mental health status of the Jinuo people could contribute much to a better understanding of the effect that modernization and urbanization have on their mental health. Also, as far as we know, this is the first paper to present a 30-year longitudinal study to follow up the schizophrenia status of an ethnic group in China since the economic reform era beginning in 1979.

Prevalence of schizophrenia in Jinuo ethnic group

In our longitudinal study, both the adjusted current prevalence and the adjusted lifetime prevalence of schizophrenia in the Jinuo people showed little change since 1979: around 2.5‰ and 4.0‰, respectively. The data suggest that during the three decades, there was no increasing trend for schizophrenia prevalence in Jinuo society. These prevalence data were lower than those in Han people in other provinces and cities of China when using the same screening and diagnosis tools, such as in Hebei Province (Cui et al., 2007).

Wechsler and Pugh (1967) believed that when people with a particular characteristic live in an area where this characteristic is less common, a higher rate of mental illness is often observed. Boydell et al. (2001) examined this with regard to ethnicity and found that incidence rates of schizophrenia increased in ethnic minority groups as the proportion of ethnic minorities decreased; this association has already been replicated by Veling et al. (2008). However, we did not find this phenomenon in the Jinuo ethnic group, and the prevalence of schizophrenia during the three decades appeared to remain stable.

One of the reasons for the above differences between our study and others might reflect the complexity of the genetic etiology of schizophrenia, since we know that some positive susceptible genes of schizophrenia such as the catechol-O-methyltransferase gene (COMT) (Hywel et al., 2005) cannot be replicated in other ethnicities. In a genetic comparative study between Han and Jinuo schizophrenia patients, a difference was found between the two ethnic groups in tryptophan hydroxylase 2 gene polymorphism (rs 1386494) (Chen et al., 2009).

Another reason might be differences in research methods. Therefore, in the present study we used the methods of the WHO collaborative study on psychological problems in general care (Von Korff & Üstün, 1995) to facilitate comparison between our results and other similar studies.

Prognosis of schizophrenia in Jinuo ethnic group

Although the prevalence of schizophrenia in the Jinuo people was lower compared to other ethnic groups in China, as it is a severe mental disorder, this is not optimistic. Even though the remission rate increased from 12.90% in 1989 to 18.87% in 2009, 62.26% of patients still had deteriorated or residual symptoms in 2009. From 1989 to 2009, the death rate gradually decreased from 29.03% to 18.87%; however, this decreasing trend was not statistically significant different according to the χ² test. In the 2009 survey, only one patient was receiving antipsychotic treatment. This huge treatment gap might be one of the major reasons accounting for the bad prognosis.

When dividing untreated patients into different groups according to illness duration, the patients whose duration was more than 20 years had the most serious negative and general psychopathological symptoms, and the highest total PANSS score. To some extent, the findings in the Jinuo ethnic group support the notion that natural, never-treated people are more likely to have a longer duration of illness, more marked symptoms and accept less support than treated individuals in rural China (Ran et al., 2009). Similarly, some authors have suggested that there is a better prognosis for individuals with schizophrenia in low- and middle-income countries (Leff, Sartorius, Jablensky, Korten & Ernberg, 1992). Our study, however, showed a contrary result, which indicated that in a region of low economic development and fewer mental health services, there is a greater need to educate the public about psychopathology, to improve the ability of professionals to identify the nature of the illness, and to pay close attention to the diagnosis, treatment, prognosis and outcomes of schizophrenia.

Gender difference of prevalence

In the present study, a gender difference of lifetime and current prevalence of schizophrenia in the Jinuo people was found. Statistical analysis showed that, in this population, prevalence of schizophrenia in males was one to three times higher than that in females. This gender difference of schizophrenia prevalence in the Jinuo people supports the idea that the schizophrenic population always displays far more gender differences than any other psychotic patient group (McGlashan & Bardenstein, 1990).

Limitations

During the survey, we only screened people who were older than 18 years. Therefore the data in this study does not illustrate the schizophrenia status of children and adolescents.

Some early data could not be analysed well and compared to the later follow-up data because we were unable to use CIDI and PANSS until the last two surveys. This limitation meant that this study could not show the change of symptoms over time.

Another limitation of this study is the small sample size. Although the total population of the Jinuo people is only 10,610, they live quite scattered across a huge mountain area, which makes it very hard to recognize and recruit schizophrenia patients. However, despite the small sample size, the power analysis showed that the sample has 71.4% reliability. Despite these limitations, our results reveal, to some extent, the association between cultural changes and schizophrenia incidence in the Jinuo people.

Footnotes

Acknowledgements

We want to express our gratitude to all subjects, JingHong Health Bureau and Jinuo Hospital, without whose cooperation this work would not have been possible. We also want to thank Professor Ronald Wintrob of Brown University for reviewing an earlier version of the article and offering suggestions for its revision.

Funding

This work has been supported by the National Natural Science Foundation of China (Grant 81160170), Natural Key Technology Research and Development Program of the Ministry of Science and Technology of China (2009BAI77B05), and the Natural Scientific Foundation of Yunnan Province (Grant 2010CD121).

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