Dual Diagnosis Health and Social Care Services Systematic Review

EXECUTIVE SUMMARY

Dual diagnosis refers to people with a severe mental illness (including schizophrenia, schizotypal and delusional disorders, bipolar affective disorder and severe depressive episodes with or without psychotic episodes) combined with the misuse of substances (the use of legal or illicit drugs, including alcohol and medicine, in a way that causes mental or physical damage). Recent studies have estimated prevalence rates of 20-37% in secondary mental health services and 6-15% in substance misuse settings (Carrà & Johnson, 2009).

However, methodological challenges including differing definitions of dual diagnosis, varying timescales for assessing comorbidity, difficulties with diagnosis including diagnostic overshadowing, and the lack of a good theoretical model of the association between severe mental illness and substance misuse, mean that it is still unclear how many people in the UK have a severe mental illness and comorbid substance misuse problems.

There is a growing awareness that individuals with dual diagnosis experience some of the worst health, wellbeing and social outcomes, and are among the most vulnerable in society.

A clear understanding of the scale of the problem, the current service (including variations), and the mechanisms of change, are vital in order to interpret differences in outcomes and costs for alternative current models of service delivery, new models of service delivery and/or aspirational models of service delivery.

The National Collaborating Centre for Mental Health (NCCMH) was commissioned by NICE Centre for Public Health (now the Public Health and Social Care Centre) to conduct 4 evidence reviews to help inform the development of a guideline aimed at optimising service organisation and delivery of community health and social care services for adults and young people with coexisting severe mental illness and substance misuse.

This systematic review of the epidemiology and current practice for individuals with dual diagnosis living in the community in the UK is the first of these 4 evidence reviews

This review considered epidemiological data derived from cohort studies, cross-sectional studies, surveys, health needs assessments, and the control arm of randomised clinical trials, and data about the current practice from surveys, cross-sectional studies and national/regional/local reports, assessments or evaluations, in order to address the following review questions:

RQ 1.1: What are the health and social care needs of people in the UK with a severe mental illness who also misuse substances?

RQ 1.2: What is the current configuration of health and social care community services and the care pathway through which people in the UK with coexisting severe mental illness and substance misuse are recognised, treated, managed and followed-up?

Severe mental illness and substance misuse (dual diagnosis) – community health and social services – Draft Review 1This review was conducted in accordance with Developing NICE Guidelines: The Manual (NICE, 2014). A systematic search was conducted in 18 electronic databases for RQ 1.1 and 3 databases for RQ 1.2 (for studies published from 2000 onwards) and 31 websites.

Given the variability across studies, particularly in a service setting and sampling frame, the results were largely summarised narratively in text and tables. In addition, some meta-analyses were possible, allowing a comparison between cases with comorbid severe mental illness and substance misuse and controls with severe mental illness-only to examine differences in the probabilities of health and social care needs associated with dual diagnosis.

Overall, 48 studies met the inclusion criteria; 36 for RQ 1.1 and 12 for RQ 1.2. The studies reporting prevalence data for RQ 1.1 (N=31) were subdivided by service setting and sampling frame: 7 studies reported prevalence data for dual diagnosis obtained using comprehensive catchment area survey sampling frames (as a percentage of the general population in a catchment area [N=2] or of individuals with severe mental illness in a catchment area [N=5]) (3 additional studies also used a comprehensive catchment area survey but did not report prevalence data); 21 studies estimated prevalence rates amongst caseloads of secondary mental health services (an additional study sampled from secondary mental health services but did not report prevalence data); 5 studies reported prevalence data for severe mental illness amongst individuals with substance misuse problems who were in contact with community drug or alcohol addiction services; 3 studies reported prevalence data for dual diagnosis across secondary mental health and substance misuse service settings; 2 studies estimated prevalence and incidence respectively amongst those in contact with primary care. Some studies reported prevalence for multiple settings and are reported in each relevant section.

Of the 36 studies identified for RQ 1.1, 13 studies were rated as high quality (++), 10 studies were rated as moderate quality (+) and the remaining 13 studies were rated as poor quality (-), based on the Newcastle-Ottawa Scale (NOS) for assessing the quality of nonrandomised studies. Of the 12 studies identified for RQ 1.2, 2 studies were rated as high quality (++), 9 studies were rated as moderate quality (+) and 1 study as poor quality (-), based on the NICE-adapted AACODS checklist (checklist 1.5 in the NICE ‘Interim methods guide for developing service guidance 2014’). The key findings from these studies are summarised below in Evidence statements.