The burden of disease among people with severe substance use disorders

Abstract

Background: A substance use disorder (SUD) is a potentially severe clinical condition with high co-occurrence of somatic and mental disorders. The burden of disease attributable to substance use contributes to 11.8 million deaths worldwide each year or 1.5% of the global disease burden. Prevalence of chronic hepatitis C (HCV) have reached endemic proportions among people with severe SUD, more than half will experience a mental health disorder at some point during their lives and it may cause poor health-related quality of life (HRQoL). Few studies have assessed HCV treatment uptake, impact of substance use patterns and mental health, or measured HRQoL as health outcome among long-term patients in opioid agonist therapy (OAT).

Methods: In paper I, HCV treatment uptake among OAT patients was estimated by medication dispensation from 2014 to 2017 in Sweden and Norway using data from nationwide registries; The Swedish Prescribed Drug Register and The Norwegian Prescription Database. HCV prevalence was estimated from a mix of primary and secondary data. Paper II and three are nested prospective cohort studies, which recruited 707 and 609 participants, respectively, across nine OAT outpatient clinics and low-threshold municipality clinics in Norway, during 2017-2020.

The ten-item Hopkins Symptom Checklist (SCL-10) and EQ-5D-5L were used to assess symptoms of mental health disorders and HRQoL. The SCL-10 involves ten items, which are each scored on four dimensions from not bothered at all (item score = 1) to extremely bothered (item score = 4). A linear mixed model analysis examined the impact of substance use patterns and sociodemographic factors on SCL-10 sum score with beta coefficients with 95% confidence intervals (CI). EQ-5D-5L measures five health dimensions on a five-point Likert scale (from no problems (item score = 1) to extreme problems (item score = 5)). A UK value set was applied to calculate index values (from 0 to 1). Self-perceived health was measured with EQ-VAS (from 0 to 100). Descriptive statistics were derived at baseline and central tendency and dispersion reported by means and standard deviation (SD).

Results: For the HCV treatment uptake study, altogether 3,529 individuals were identified with dispensed OAT in the Swedish cohort and 7,739 individuals in the Norwegian cohort. HCV prevalence was estimated to be over 50%. Calculations showed that annual HCV and DAA treatment uptake increased in both countries. The estimated cumulative HCV treatment uptake among people in need of HCV treatment at the end of 2017 was 28% in Sweden and 31% in Norway. In Sweden, DAA treatment was associated with increased age (adjusted odds ratio (aOR) 1.8; 95% CI 1.0-3.2) and dispensation of drugs used for diabetes (aOR 3.2; 95% CI 1.8-5.7), whereas in Norway, dispensation of cholesterol modifying agents and antibacterials were associated with decreased odds (aOR 0.4; 95%CI 0.2-0.9, aOR 0.8; 95%CI 0.6-1.0).

Overall, many individuals reported considerable mental distress and impaired HRQoL. The mean (SD) SCL-10 score for all items was 2.2 (0.8) at baseline, which showed that 65% of the cohort had a mean score >1.85, the standard threshold for likely mental health disorders. Among people with frequent use of substances, more symptoms of mental health disorders were observed amid those using benzodiazepines (3.6, 95% CI:2.4;4.8), cannabis (1.3, 0.2;2.5), opioids (2.7, 1.1;4.2) compared to those with no or less frequent use of these substances. On the contrary, less mental health symptoms were observed among people using frequently stimulants (-2.7, -4.1;-1.4). The study also showed that females (1.8, 0.7;3.0), having debt worries (2.2, 1.1;3.3) and unstable living conditions (1.7, 0.0;3.3) were associated with higher burden of mental health symptoms. There were large individual variations in SCL-10 score from baseline to follow-up, but no consistent time trends indicating change over time for the whole cohort.

The mean (SD) EQ-5D-5L index value at baseline was 0.7 (0.3) and EQ-VAS 57 (22) compared to 0.9 (0.2) and 80 (19) for the Norwegian reference population. The study found large individual variations in index values, where 43% had >0.8 and 5% had <0.2 at baseline. The lowest EQ-5D-5L index values were observed for female patients, age groups older than 40 years and for methadone users. At follow-up, improvements in HRQoL were observed across almost all health dimensions. Mean (SD) overall index value and EQ-VAS at follow up were 0.7 (0.2) and 59 (22) respectively.

Conclusion: This thesis has revealed numerous challenges related to people with severe SUD, in addition to being a very heterogeneous population. Despite increased HCV treatment uptake in both Sweden and Norway it was estimated that more than two thirds of the OAT populations in need of treatment were left untreated at the beginning of 2018. While the vast majority is experiencing a high burden of mental health symptoms and considerable impaired HRQoL, around one third had few mental health symptoms and very good HRQoL. These findings emphasize the urgent need for more research, and perhaps more gender-and age-adopted treatment. The wide variations seen in SCL-10 and HRQoL support more focus on individualized treatment and personalized patient care, and the need for regular assessment of these health outcomes in SUD and OAT treatment programs.