The prevalence and disability of bipolar spectrum disorders in the US population: re-analysis of the ECA database taking into account subthreshold cases.

BACKGROUND: Despite emerging international consensus on the high prevalence of the bipolar spectrum in both clinical and community samples, many skeptics contend that narrowly defined bipolar disorder with a lifetime rate of about 1% represents a more accurate estimate of prevalence. This may in part be due to the fact that higher figures proposed for the bipolar spectrum (5-8%) have not been based on national data and have not included all levels of manic symptom severity. In the present secondary analyses of the US National Epidemiological Catchment Area (ECA) database, we provide further clarification on this fundamental public health issue.
METHODS: All respondents in the first wave (first interview) of the ECA household five site sample (n=18252) were classified on the basis of DSM-III criteria into lifetime manic and hypomanic episodes, as well as those with at least two lifetime manic/hypomanic symptoms below the threshold for at least 1 week duration (subsyndromal manic symptoms [SSM] group). Odds ratios were calculated on lifetime service utilization for mental health problems, measures of adverse psychosocial outcome, and suicidal behavior compared to subjects with no mental disorders or manic symptoms.
RESULTS: As originally reported nearly two decades ago by the primary investigators of the ECA, the lifetime prevalence for manic episode was 0.8%, and for hypomania, 0.5%. What is new here is the inclusion of subthreshold SSM subjects, which accounted for 5.1%, yielding a total of 6.4% lifetime prevalence for the bipolar spectrum. All three (manic, hypomanic and SSM) groups had greater marital disruption. There were significant increases in lifetime health service utilization, need for welfare and disability benefits and suicidal behavior when the SSM, hypomanic and manic subjects were compared to the no mental disorder group. Suicidal behavior was non-significantly highest in the hypomanic (bipolar II) group. Otherwise, hypomanic and manic groups had comparable level of service utilization and social disruption. LIMITATIONS: Comorbid disorders, which might influence functioning, were not included in the present analyses.
CONCLUSION: These secondary analyses of the US National ECA database provide convincing evidence for the high prevalence of a spectrum of bipolarity in the community at 6.4%, and indicate that subthreshold cases are at least five times more prevalent than DSM-based core syndromal diagnoses at about 1%. These SSM subjects, who met the criteria of "caseness" from the point of view of harmful dysfunction, are of great theoretical and public health significance.