# Comparison of Mental Illness Comorbidity Pre-Pandemic vs. Pandemic-Era and Associations with Clinical and Demographic Characteristics for Virginia Public Hospital Inpatient Discharges with a Substance Use Disorder

## TL;DR

This study compares mental illness comorbidity in patients with substance use disorders before and during the pandemic, finding significant increases and associations with demographics and physical health conditions.

## Contribution

The study is the first to examine pandemic-era increases in mental illness comorbidity among inpatients with substance use disorders and their associations with physical and demographic factors.

## Key findings

- Mental illness comorbidity significantly increased from pre- to post-pandemic (p < 0.0001).
- Comorbid mental illness was significantly associated with age, race, sex, and physical illnesses (p < 0.0001).
- Children/adolescents, females, American Indians, and those with HIV/AIDS had the highest comorbidity rates.

## Abstract

Public health relevance—How does this work relate to a public health issue?
Substance use disorders are of great public health concern given their high prevalence and associated mortality, morbidity, and socioeconomic burden.Patient discharge data enable the study of public health issues through large population-based datasets.

Substance use disorders are of great public health concern given their high prevalence and associated mortality, morbidity, and socioeconomic burden.

Patient discharge data enable the study of public health issues through large population-based datasets.

Public health significance—Why is this work of significance to public health?
While increases in mental illness rates are well documented, it is not known whether the increases in rates of mental illness are increases in single mental illness diagnoses or comorbid mental illness diagnoses.The specific associations between COVID-19, physical illness, and mental illness comorbidity have not been studied before among inpatients with SUD.

While increases in mental illness rates are well documented, it is not known whether the increases in rates of mental illness are increases in single mental illness diagnoses or comorbid mental illness diagnoses.

The specific associations between COVID-19, physical illness, and mental illness comorbidity have not been studied before among inpatients with SUD.

Public health implications—What are the key implications or messages for practitioners, policy makers, and/or researchers in public health?
It is important for healthcare leaders to be aware of increases in comorbid mental illnesses as they may interact and affect the course and prognosis of these illnesses.These findings are important for healthcare leaders as new highly transmissible coronavirus subvariants are rising worldwide, chronic physical illnesses such as obesity and hypertension remain major healthcare challenges, and SUD and mental illness rates continue to increase.

It is important for healthcare leaders to be aware of increases in comorbid mental illnesses as they may interact and affect the course and prognosis of these illnesses.

These findings are important for healthcare leaders as new highly transmissible coronavirus subvariants are rising worldwide, chronic physical illnesses such as obesity and hypertension remain major healthcare challenges, and SUD and mental illness rates continue to increase.

The rise in mental illnesses after the COVID-19 pandemic is well documented. However, it is not known whether the rates of mental illness comorbidity increased. The objectives of this study were to compare mental illness comorbidity rates before and after the pandemic among inpatients with SUD and to test associations between mental illness comorbidity, physical illness, and demographics. We used a retrospective cross-sectional design in a sample of inpatient discharges (N = 233,017) at Virginia public hospitals from January 2018 to December 2022. We used Z tests to compare rates of mental illness comorbidity pre- and post-pandemic and Chi-square tests to examine associations of mental illness comorbidity with physical illness and demographics. Single and comorbid mental illness significantly increased from pre- to post-pandemic, p < 0.0001. Mental illness comorbidity was significantly associated with sex, age, race, insurance, COVID-19/Long COVID, HIV/AIDS, COPD, hypertension, obesity, CVD, cancer, and diabetes (p < 0.0001). There was a significant increase in mental illness comorbidity, which was significantly associated with age, race, sex, and physical illnesses. Children/adolescents, females, American Indians, and individuals with HIV/AIDS had the highest rates of mental illness comorbidity. Public health action is needed to address the increase in complex medical needs among people with SUD.