The detection of CHR samples in both the clinical settings[10, 33-36] and non-clinical settings[31, 37, 38] attracted a great deal of attention around the world, while the detection rate of CHR subjects in these studies varied considerably. Previous studies reported that the prevalence of CHR in the clinician-referred samples was 32-42%[33-35], which correspond roughly to one another. While the detection rate in samples of help-seeking individuals ranged from 4.2% to 80%, which varied from site to site[10, 39-41]. For the general population (primarily focused on young adults and adolescents), the annual incidence of new cases of CHR was estimated at 1/10 000[33], and the prevalence ranged from 0.3% to 2.4%[31, 37, 38]. The diagnostic instruments were considered to be a great factor contributing to the inconsistency of the detection rate. Schultze et al.[31] screened CHR in a young adult community with SIPS and SPI-A, and reported that 2.4% of the participants met at least one CHR criterion, while only 0.6% met the APS criteria identified by the SIPS. Salazar et al.[42] reviewed 56 studies and suggested that the 0.3% of the general non-help-seeking population of youth met the DSM-5-APS criteria, while 1.3% of the general population met the SIPS-APSS criteria. In this study, the detection rate of CHR subjects identified based on the SIPS criteria in Chinese college students was 0.3%. To our knowledge, this is the first multicentre epidemiological study on the detection of CHR subjects in Chinese college students. The participants were recruited from three different cities, including highly developed cities like Shanghai and Nanjing, and also a second-tier city like Nanchang, through a random sampling way. In addition, the colleges involved included both general higher educational institutions and vocational colleges. Therefore, the sample in the present study was representative of Chinese college students. Although the detection rate reported in our study was below 1.1% in a single-centered study of Chinese college students[38], it was generally consistent with other studies mentioned above.
Since first-episode psychosis usually occurs in late adolescence and early adulthood, CHR or prodromal psychosis were believed to have an earlier onset[43, 44]. Our research demonstrated that the peak age range of the CHR identification by SIPS was between 17 to 20 years in the sample of Chinese college students, which was largely in line with previous studies, but somewhat narrower (e.g. SHARP reported 16 to 21 years in a Chinese sample)[10, 27]. The mean age of CHR was 18.3 (SD=1.5) years in this sample, which was similar to the sample of NAPLS[33], but younger than that of SHARP[10], and older than that of RAP[27]. The demographic chracteristics of the participants enrolled in these studies may account for the age discrepancy. As the participants recruited in this study were college students with an age range of 14 to 31 years, while NAPLS recruited clinician-referred subjects aged 12 to 35 years, SHARP included help-seeking subjects aged 15 to 45 years, and RAP included help-seeking subjects aged 12 to 22 years.
Similar to previous studies using PQ-B to screen CHR in Chinese population[16, 22, 45-47], our research proved that PQ-B could be a feasible first-step tool to detect suspected CHR subjects in college students. Both the sensitivity and specificity of PQ-B were excellent in this study. Also, the results showed that 8 items of PQ-B including the PQ1 (asking “Do familiar surroundings sometimes seem strange, confusing, threatening or unreal to you?”), the PQ3 (asking “Do things that you see appear different from the way they usually do (brighter or duller, larger or smaller, or changed in some other way)?”), the PQ4 (asking “Have you had experiences with telepathy, psychic forces, or fortune telling?”), the PQ12 (asking “Do you worry at times that something may be wrong with your mind?”), the PQ13 (asking “Have you ever felt that you don't exist, the world does not exist, or that you are dead?”), the PQ15 (asking “Do you hold beliefs that other people would find unusual or bizarre?”), the PQ17 (asking “Are your thoughts sometimes so strong that you can almost hear them?”) and the PQ18 (asking “Do you find yourself feeling mistrustful or suspicious of other people?”) had significant predictive value of SIPS diagnosis, which indicated that delusional ideas, perceptual abnormalities and suspiciousness were key symptoms in identifying CHR subjects. Similarly, Xu et al.[22] and Schultze et al.[31] also reported that perceptual abnormalities, delusional ideas and suspiciousness were the most prevalent psychosis-risk symptoms.
Nevertheless, our results recommended higher cutoff points for the total score and distress score of PQ-B (13 and 46) than those of SHARP did in the Chinese population (7 and 24)[22], which were also much higher than the cutoff points reported in the initial validation study of PQ-B (3 and 6)[16]. Despite the cultural background and language may lead to the differences of PQ-B cutoff points[48], there are still other reasons underlying the differences between the present study and SHARP. First, the participants in this study were college students who were tested with PQ-B in non-clinical settings (online or in the colleges), while SHARP recruited help-seeking outpatients from a psychological counselling center[22]. As prodromal symptoms mentioned in PQ-B were easily mixed with psychotic-like experiences (PLEs) that commonly existed in the general population[49-52], subjects who only had PLEs may also be tested positive with PQ-B, causing false positives. In addition, being rated in a clinical setting, rather than a non-clinical setting, may help the participants better understand the prodromal symptoms mentioned in the scale, and thus reducing false positive errors. Indeed, if we used the same cutoff points as SHARP did in their screening procedure, 72.0% (16595/23063) of the participants would be screened positive with PQ-B in this study, while the positive rate of PQ-B in SHARP was 62.1% (1681/2705)[10], which may indicate that our false positive rate in PQ-B screening was higher. Second, the screening procedure differed. SHARP employed a 2-stage method where the PQ-B-positive subjects would all be invited to the SIPS interview, and 18.3% of the PQ-B-negative subjects were also interviewed[10]. However, we used a 3-stage method that applied a telephone interview to the PQ-B-positive subjects, and only subjects screened as positive in the telephone interview were invited to the SIPS interview. Moreover, no further investigations were provided to the negative subjects in the present study. These variance in the screening procedure may have contributed to the underestimation of CHR subjects, which would interfere the examination of the psychometric properties of PQ-B.
As discussed in the last paragraph, the telephone assessment can cause the missed diagnosis of CHR, which was a limitation of this study, whereas, it saved a lot of human resources in the process of CHR screening, in fact, particularly in a large sample of general population. It is worth mentioning that the telephone assessment employed in this study was not a semi-structured or structured interview that can be seen in other studies, although we also use SIPS as the assessing instrument[31, 53, 54]. In the present study, researchers only needed to ask questions following the SIPS subscale for positive symptoms, and to rate the severity for each domain based on the participants’ subjective reports. Consequently, it only took 5 minutes on average, which was much time-saving compared to a structured/semi-structured interview. In fact, it has also enhanced the screening efficiency by preventing almost 90% of the PQ-B-positive subjects from receiving a face-to-face SIPS interview, despite the fact that it was, of course, based on the sacrifice of the detection rate.
Another limitation is that, due to limited resources, the information received from the participants was incomplete. On the one hand, we missed some important clinical features of the subjects, including family history and psychiatric comorbidity. On the other hand, the CHR subjects were not followed after being diagnosed, and therefore the transition to psychosis or other mental disorders was not investigated in this study.