Grading disorder severity and averted burden by access to treatment within the GBD framework: a case study with anxiety disorders

Background: The Global Burden of Disease Study (GBD) estimates burden by cause with major relevance for resource allocators globally. Non-fatal burden estimates are influenced by disorder severity. However, for many disorders, global severity is sourced from a single high-income country survey. We aimed to estimate severity distributions that vary by Healthcare Access Quality Index (HAQI) using anxiety disorders as a case study and present the usefulness of this method in simulating averted and avoidable burden globally. Methods: In this case study, we estimated treatment use among respondents with anxiety disorder in the 1997 Australian National Survey of Mental Health and Wellbeing (NSMHWB), the source used to estimate severity of anxiety disorders in GBD. Treatment effects were sourced from the Cochrane Database of Systematic Reviews and pooled via network meta-analysis. Severity distribution was established via a meta-regression of their disability weights, derived from 12-item short form survey scores. We simulated the shift in severity across scenarios without access to treatment and with full access to optimal treatment (cognitive behavioural therapy and antidepressants). We interpolated this shift linearly along the HAQI, extrapolated country-specific severity from HAQI scores, and calculated averted and avoidable burden. Findings: The database review sourced 56 reviews, of which eight were eligible for inclusion. These eight reviews reported on 156 randomised controlled trials, with 194 treatment effects. Respondents to the 1997 NSMHWB consisted of 5936 women (55·8%) and 4705 (44·2%) men aged 18 years or older (mean age and ethnicity data not available). The survey-weighted treatment effect size was –0·28 (95% uncertainty interval –0·45 to –0·12). The pooled treatment effect for full coverage optimal treatment was –1·07 (–1·47 to –0·64). The sequela-weighted disability weight among people with anxiety disorder in the NSMHWB was 0·141 (0·042 to 0·275). The estimated disability weight was 0·188 (0·070 to 0·341) after removing the benefits of treatment and 0·056 (0·013 to 0·140) after providing all people with anxiety disorder access to optimal treatment. Globally, 12·5% (4·6 to 21·5) of anxiety disorder burden was averted because of available treatment. However, 71·1% (46·2 to 87·6) of global anxiety disorder burden could be averted if all people with anxiety disorders had access to optimal treatment. Interpretation: Because it is based on guidance from a single survey done in one high-income country, the burden of anxiety disorders in low-income and middle-income countries is probably underestimated by GBD. Despite the availability of effective treatments, low use of these treatments means that most burden is still avoidable. Most of the burden could be averted if all people with anxiety disorders had access to optimal treatment, highlighting the importance of public promotion and referral pathways of treatment for anxiety disorders. Location-specific severity distributions in GBD would greatly increase precision in burden estimates and highlight avertable burden to clinicians, public health practitioners, and policy makers. Funding: Queensland Health and Bill & Melinda Gates Foundation.