Changes in the prevalence of bipolar disorders between 1998 and 2008 in an Australian population

Abstract

To identify any changes in the prevalence of bipolar disorder (BD) between 1998, 2004, and 2008. Cross-sectional population-based surveys were conducted involving random and representative samples of South Australian adults aged ≥ 15 years. BD was assessed using the mood module of the Primary Care Evaluation of Mental Disorders instrument (PRIME-MD), a single question related to doctor-diagnosed BD and the Mood Disorder Questionnaire (MDQ), which defines bipolar spectrum disorder. The PRIME-MD-derived prevalence of BD increased significantly from 0.5% [95% confidence interval (CI): 0.27-0.79] in 1998 to 1.0% (95% CI: 0.61-1.31) in 2004 and 1.5% (95% CI: 1.05-1.91) in 2008, demonstrating a significant increased linear trend (χ² =13.91, df=2, p=0.002). Similarly, reported doctor-diagnosed BD increased significantly from 1.1% (95% CI: 0.75-1.51) in 1998 to 1.7% (95% CI: 1.26-2.18) in 2004 and 2.9% (95% CI: 2.28-3.48) in 2008 (Linear trend test χ²=24.55, df=2, p<0.001). The MDQ-derived diagnosis of bipolar spectrum disorder changed from 2.5% (95% CI: 1.96-3.08) in 2004 to 3.3% (95% CI: 2.66-3.94) in 2008 (χ² =3.22, df=1, p<0.10), but this difference did not attain statistical significance. Confining the analysis to those positive for BD on all three methods, there was a significant increase in the prevalence of the detection of BD using all three measures (χ² =4.43, df=1, p=0.03) between 2004 and 2008. There has been an increased prevalence of BD in South Australia over the last decade, but this may be related to changing diagnostic practices rather than a true increase.