Schizophrenia Quiz: Epidemiology and Risk Factors

• The male:female ratio for the incidence of schizophrenia is approximately 1.4:1.

• However, as age increases, the onset of schizophrenia is more common in women. 

• Overall, men with schizophrenia have worse premorbid adjustment, greater negative symptoms and substance use comorbidity, and less depressive symptoms than women.

Source: Abel KM, Drake R, Goldstein JM. Sex differences in schizophrenia. Int Rev Psychiatry. 2010; 22:417.

• In this umbrella review, twin birth was associated with a non-significant increased risk of psychosis (OR=1.53, 95% CI 0.79-2.97). 

• Six risk factors had “highly suggestive” evidence, including ethnic minority in low ethnic density area, second generation immigrants, trait anhedonia, premorbid IQ, minor physical anomalies, and olfactory identification ability.

Radua J, Ramella-Cravaro V, Ioannidis JP, et al. What causes psychosis? An umbrella review of risk and protective factors. World Psychiatry. 2018;17:49-66.

• In this review, Ultra-high-risk state for psychosis (OR=9.32, 95% 4.91-17.72) and Black-Caribbean ethnicity in England (OR=4.87, 95% 3.96-6.00) were the risk factors with the most convincing evidence for association with psychosis.

Radua J, Ramella-Cravaro V, Ioannidis JP, et al. What causes psychosis? An umbrella review of risk and protective factors. World Psychiatry. 2018;17:49-66.

• A meta-analysis found a significant association between schizophrenia and infection by Human Herpesvirus 2 (OR=1.34; CI 95%: 1.09–1.70), Borna Disease Virus (OR=2.03; CI 95%: 1.35–3.06), Human Endogenous Retrovirus W (OR=19.31; CI 95%: 6.74–55.29), Chlamydophila pneumoniae (OR=6.34; CI 95%: 2.83–14.19), Chlamydophila psittaci (OR=29.05; CI 95%: 8.91–94.70) and Toxoplasma gondii (OR=2.70; CI 95%: 1.34–4.42).

• By contrast, there was not a significant association between risk of schizophrenia and exposure to Epstein-Barr virus, human herpesvirus (HHV)-1, HHV-2, HHV-6, varicella zoster virus, or cytomegalovirus

• The observation that a myriad of different infectious agents-bacteria, viruses, and protozoans-are association with schizophrenia risk raises the possibility that that the immune response to infection may play a role.

Arias I, Sorlozano A, Villegas E, de Dios Luna J, McKenney K, Cervilla J, Gutierrez B, Gutierrez J. Infectious agents associated with schizophrenia: a meta-analysis. Schizophr Res. 2012;136:128-36.

• A meta-analysis found a significant association between all of these risk factors and schizophrenia, but the association was strongest for diabetes in pregnancy (OR=7.76, 95% CI 1.37-43.90).

• Other obstetric complications that were significantly associated with schizophrenia risk in offspring included: congenital malformations, asphyxia, and bleeding in pregnancy.

Cannon M, Jones PB, Murray RM. Obstetric complications and schizophrenia: historical and meta-analytic review. Am J Psychiatry. 2002;159:1080-1092.

• A meta-analysis of 35 samples found an estimated 33.7% prevalence of comorbid cannabis use in patients with first-episode psychosis (95% CI 31-39%).

• The pooled estimate for the interval between initiation of regular cannabis use and age of onset of psychosis was 6.3 years.

Myles H, Myles N, Large M. Cannabis use in first episode psychosis: Meta-analysis of prevalence, and the time course of initiation and continued use. Aust N Z J Psychiatry. 2016;50:208-219.

This quiz was originally posted on March 5, 2018 and has since been updated.