Comorbidities within mental illnesses in a multiethnic urban population.

The prevalence and patterns of comorbidities among mental illnesses including substance misuse have been rarely documented in urban communities. In this study, we aimed to examine the prevalence, diagnostic patterns, common risk factors and functioning associated with comorbid mental illness among community residents in an urban population. Using data from Singapore Mental Health Study (SMHS) 2010 (n = 6616) and SMHS 2016 (n = 6126), we investigated the changes in the overall prevalence of comorbid mental illness and the diagnostic patterns of multiple affective disorders, affective disorder comorbid with substance misuse and multiple substance misuse. The most common diagnostic pair of comorbid affective disorder was major depressive disorder (MDD) and obsessive-compulsive disorder (OCD) (0.4 % at 2010 and 0.7 % at 2016). Among comorbid substance misuse, comorbidity of MDD and alcohol related disorder (ARD) was most frequent (0.5 % and 0.7 % respectively), while comorbidity of nicotine dependence (ND) with ARD decreased from 0.5 % to 0.1 %. Logistic regression was utilized to identify the associations of socio-demographics/clinical characteristics with patterns of comorbid mental illness and the associations of number of comorbid mental illness with impaired functioning. The risk profileassociated with comorbid mental illnesses differed among various comorbidity groups. Moreover, in SMHS 2016, higher number of comorbidities within mental illness was associated with higher odds of functioning impairment. The increase in the prevalence of comorbid mental illnesses indicates the need for early diagnosis and integrated disease management. Moreover, certain subgroups in the general population are more at risk of comorbid mental illnesses.