CDC’s DOSE System leverages health record data to identify, track, and respond to emerging trends in NFODs within and among 47 states and the District of Columbia (hereafter, states) receiving funding for participation (A.M. Vivolo-Kantor et al., 2021). Twenty-five states submitted aggregate discharge data to CDC for ED visits only (N=4 states), hospitalizations only (N=3 states), or both (N=18 states) on a quarterly basis, with a one-quarter time lag (e.g., data from October–December 2019 were submitted in April 2020) for the time period January 1, 2018, through December 31, 2020. Discharge data on over 90% of all emergency visits (ED and hospitalization) within each included state are reported. Data include counts of NFOD-related ED visits and hospitalizations for four drug categories (all drugs, all opioids, heroin, and all stimulants), by county of patient residence, based on International Classification of Diseases, 10th Revision, Clinical Modification (ICD-10-CM) discharge diagnosis codes submitted for medical billing (A. Vivolo-Kantor et al., 2021). State reporting by county of patient residence excludes nonresident NFOD visits. Additionally, patients initially treated in an ED and subsequently admitted to the hospital were excluded from the ED visit dataset. Case definitions were nested; for example, an individual experiencing a heroin overdose would also be categorized as an all opioid overdose and an all drug overdose. Self-harm NFODs, which were identified by ICD-10-CM codes for intentional/self-harm poisonings, were excluded from analysis.

Two of the 25 states had incomplete county-level data and were excluded from analyses due to incomplete reporting (Nebraska and Oklahoma), leaving 20 states (1449 counties) submitting ED data and 19 states (1279 counties) submitting hospitalization data (Fig. 1).

We used the SVI to measure county-level social vulnerability, which comprises 15 ACS variables used to rank U.S. counties from 0 to 1 (low to high relative vulnerability), with an overall composite rank score, four SVI theme scores, and: (1) Socioeconomic Status (individuals below poverty level, unemployment among civilians aged ≥16 years, per capita income, adults aged ≥25 years with no high school diploma), (2) Household Composition and Disability (persons aged ≥65 years, persons aged ≤17 years, population living with disability, single-parent households), (3) Minority Status and Language (population identifying as members of a racial or ethnic group other than White, non-Hispanic, speak English “less than well”), and (4) Housing Type and Transportation (multi-unit housing, mobile homes, crowded housing, group quarters, and vehicle access). 2018 SVI data were obtained from CDC/Agency for Toxic Substances and Disease Registry’s (ATSDR’s) Geospatial Research, Analysis, and Services Program’s (GRASP’s) publicly available database, which represents the most current sociodemographic census data available for U.S. populations at the time of analysis. SVI methodological documentation, including calculation of relative vulnerability, is available from GRASP (Centers for Disease Control and Prevention, 2018). In addition to the SVI variables, we examined percentage uninsured, a variable included with the SVI data but not incorporated into the index, and urbanicity. Patient county of residence urbanicity was dichotomized as rural (referent; non-core counties) and urban (large metropolitan counties, medium/small metropolitan counties, and micropolitan urban clusters), based on the National Center for Health Statistics’ 2013 Urban-Rural Classification Scheme for Counties (Centers for Disease Control and Prevention, 2013). We classified overall SVI, themes, and individual variable scores into quartiles (using national percentile cutoffs) for our analyses (Q1=lowest vulnerability to Q4=highest vulnerability).

From January 2018 through December 2020, 537,549 all drug NFOD ED visits were reported to DOSE by the 20 states reporting ED visits. During this time, all drug NFOD rates increased 6.4% (115.7 per 100,000 to 123.2); opioid-involved overdoses increased 31.0% from 43.2 to 56.6, and heroin-involved overdoses increased 4.4% from 27.1 to 28.3; all changes were significant. Quarterly all drug, all opioid-, heroin-, and all stimulant-involved NFOD rates demonstrated seasonality, where the highest rates for each drug category were reported July–September, and the lowest rates were reported October–March during the study period (Fig. 2).

All drug, all opioid-, heroin-, and all stimulant-involved NFOD rates increased as overall social vulnerability increased; however, the highest rates were found among the Q3 vulnerability counties for overdoses involving all drugs (aRR= 1.44, 95% CI: 1.42–1.46), all opioids (aRR=1.55, 1.51–1.59), and heroin (aRR= 1.61, 1.53–1.70). In contrast, all stimulant-involved NFOD rates were highest among the most vulnerable counties (Q4 aRR=1.75, 1.66–1.84). A similar pattern was seen in Theme 1 (SES) and Theme 4 (housing and transportation) (Table 1). NFOD rates for all four drug categories were highest in the counties with highest Theme 2 (household and disability) vulnerability, and rates in all categories were lowest in counties with highest Theme 3 (minority status) vulnerability, indicating that counties with larger minority populations had lower ED visit NFOD rates.

Among ED visits, many socioecological factors were found to be associated with higher NFOD rates for all categories. Counties with higher percentages of unemployment, adults with no high school diploma, people with a disability, or single parent households had higher NFOD rates involving all drugs, all opioids, heroin, and all stimulants. Counties with the highest percentage population with no vehicle had higher NFOD rates than counties with the lowest percentage; other quartiles had equivalent or slightly lower NFOD rates compared to Q1. In general, lower NFOD rates were associated with counties where a greater proportion of people were older, uninsured, or living in crowded housing. As county minority population increased, ED NFOD rates decreased or remained equivalent for heroin-involved and stimulant-involved NFOD. Compared to counties with the lowest percentage of residents identifying as part of a racial or ethnic minority group, counties with the next lowest percentage of residents identifying as part of a racial or ethnic minority group (Q2) were marginally associated with higher all drug and all opioid-involved NFOD rates; however, counties with the highest percentage of residents identifying as part of a racial or ethnic minority group (Q3 and Q4) were associated with lower or equivalent rates of all drug or all opioid-involved NFOD rates compared to Q1.

Stimulant-involved NFODs displayed several inverse associations compared to the other drug categories. All drug, all opioid-, and heroin-involved NFOD rates were highest in urban counties and in those counties with the highest percentage of multi-unit housing, and lowest in counties with the highest percentage of younger people and highest percentage of population living in group quarters. Additionally, greater percentage of mobile home housing was associated with lower or equivalent All drug, all opioid-, and heroin-involved NFOD rates. All stimulant-involved NFOD rates were slightly lower in urban counties and slightly higher in counties with more group quarters and mobile home housing. Unlike the results that were found with other drug categories, percentage multi-unit housing and population ≤17 years generally were not associated with all stimulant-involved NFOD rates.

From January 2018 through December 2020, 182,274 all drug NFOD hospitalizations were reported to DOSE by the 19 states in our hospitalizations analysis. The all drug NFOD rates among patients decreased 7.4% during this period (55.6 per 100,000 to 51.5). All opioid- and heroin-involved NFOD rates remained stable at 18.7 and 5.6, respectively, and all stimulant-involved NFOD rates increased 4.2% from 10.8 to 11.2; however, the decrease in the all-drug NFOD rate was the only significant change among hospitalized NFODs. Like ED visits, quarterly NFOD hospitalization rates fluctuated seasonally across drug categories. The highest rates were reported April–September, and the lowest rates were reported October–March each year (Fig. 2).

Similar to NFOD ED visit rates, increased overall county-level social vulnerability was associated with higher NFOD hospitalization rates involving all drugs (Q4 aRR=2.30, 2.14–2.48), all opioids (Q4 aRR=1.86, 1.70–2.04), heroin (Q3 aRR=2.09, 1.81–2.40), and all stimulants (Q4 aRR=3.60, 3.35–3.86) (Table 2). Among hospitalizations, higher county-level vulnerability for SVI themes 3 and 4 (minority status and housing and transportation, respectively) was associated with increased NFOD rates for all four drug categories. Theme 1 (SES) NFOD hospitalization rates increased with increasing vulnerability across all drug categories in Q2 and Q3 vulnerability quartiles, however compared to the least vulnerable counties (Q1), hospitalization rates in the most vulnerable counties (Q4) only increased for all drug NFODs. Additionally, Q4 all opioid-involved and all stimulant-involved NFOD rates were equivalent to those in Q1, while all heroin-involved NFOD rates were lower in Q4 counties. Conversely all drug NFOD rates increased as vulnerability increased For Theme 2 (household and disability), the most vulnerable counties had equivalent rates to the least vulnerable, except all stimulant-involved NFOD, for which rates were higher among the most vulnerable counties. Twenty-one percent of NFOD hospitalizations involved stimulants, while only 6.7% of NFOD ED visits involved stimulants. Heroin-involved NFODs made up a smaller proportion of hospitalizations (10.2% of NFODs) compared to ED visits (22.6%).

Our analysis of the individual SVI variables found that counties with higher percentage of people with a disability, single-parent households, higher levels of unemployment, and population living in multiunit structures or crowded housing generally had higher NFOD hospitalization rates involving all drugs, all opioids, heroin, and all stimulants. While increased county population adults with no high school diploma was associated with increased all drug, all opioid-, and heroin-involved NFOD rates, this was not associated with stimulant-involved NFOD rates.

Lower NFOD hospitalization rates were associated with higher percentages of senior or youth populations. Additionally, counties with the highest percentage of population living in group quarters or uninsured (Q4) were associated with lower or equivalent NFOD rates across the four drug categories. Lower NFOD rates were not observed in the other quartiles, where NFOD rates were equivalent or higher. Unlike NFOD ED visits, counties reporting the highest percentage (Q4) of people from racial and ethnic minority groups were associated with higher all drug, all opioid-, heroin-, and all stimulant-involved NFOD rates. While the percentage of the population reporting to speak English “less than well” does not exhibit as consistent a pattern, NFOD hospitalization aRRs were generally higher than NFOD ED aRRs. Additionally, NFOD hospitalization rates were more strongly associated with urbanicity than NFOD ED visit rates were. Compared to rural counties, NFOD hospitalization rates in urban counties were higher for those involving all drugs (aRR=1.99, 1.87–2.12), all opioids (aRR=2.54, 2.24–2.87), heroin (aRR=9.65, 3.69–25.19) and all stimulants (aRR=3.28, 2.38–4.50).

With respect to limitations, this study focused on county-level SVI characteristics without inclusion of individual-level sociodemographic characteristics, which may modify associations with substance use outcomes (Boardman et al., 2001). While we evaluated the association between county percentage of people from any racial and ethnic minority group and NFOD, identified associations may vary between racial and ethnic minority groups as well as by sex or age and warrant further research. Improvements to demographic data in overdose surveillance sources would allow public health to better address disparities. Additionally, while the SVI includes many relevant sociodemographic variables, it was designed for disaster management and does not include several indicators that may contribute to substance use and overdose inequities. These include mental health, incarceration, and healthcare provider access, as well as individual racial and ethnic groups (Centers for Disease Control and Prevention, 2021). Development and validation of a drug overdose-specific index that includes additional demographic, prescription drug monitoring program, criminal justice, and mental health variables could better characterize geographic vulnerability and magnitude of associations between SDOH and NFOD. The overall and theme-level vulnerability scores for each county are summations of the theme level and individual variable scores, respectively; however, variables may have differential impact on NFOD rates.

This study period comprises years leading up to and including the onset of the COVID-19 pandemic, which in 2020 was associated with significant decreases in all-cause ED visits and increases in overdose-related ED visits and overdose-related deaths, as compared to 2019 and early 2020 (Hartnett et al., 2020; Holland et al., 2021; Kariisa, 2022). The main analysis did not stratify NFOD rates by year, and therefore, the impact of the pandemic on associations between 2020 NFOD rates and SVI characteristics is not described. Additionally, the pandemic may have impacted community-level social vulnerability, as trends in community characteristics, such as proportion of adults who were unemployed, housing stability, and food security rapidly shifted across the United States (Budget and Policy Priorities, 2021).

Finally, DOSE leverages administrative discharge diagnosis-coded data not originally collected for surveillance purposes (i.e., primary purpose is for medical billing); thus, counts from this data source may not provide accurate NFOD cost estimates. NFOD cost estimates of the four drug categories are reported to DOSE as aggregate counts; therefore, polysubstance use and analysis of drug categories not reported to DOSE (e.g., benzodiazepine, cocaine) could not be examined in this analysis. Furthermore, an ICD-10-CM code for methamphetamine poisoning was not available during our study period, while an ICD-10-CM code for fentanyl poisoning was only introduced during the last quarter of our study period; hence, these types of overdoses could not be analyzed specifically. While included states provided data from over 90% of their healthcare facilities, this analysis was not nationally representative, and some states report only ED data (n=4) or only hospitalization data (n=3). Therefore, differences between ED and hospitalization findings may be influenced by these geographic differences. While we did adjust for urbanicity in our analysis, we did not account for spatial geographic clustering. States exclude from county-level discharge data ED visits and hospitalizations for individuals who were not a resident of the state, which may artificially decrease NFOD rates within the patient’s county of residence if they reside in another state included in the analysis.

As nonfatal and fatal overdoses continue to rise, more community-level interventions that address risk factors at all socioecological levels are needed. The findings of this study highlight community-level characteristics associated with increased NFOD rates including urbanicity, common types of housing (e.g., multi-unit, group quarters), population demographics including minority status, disability, single-parent households, and unemployment and how the magnitude of these associations differs between ED visit and hospitalization NFOD. Increasing public awareness of inequities associated with increased overdose rates in all communities may decrease stigma and raise support for programs that address the underlying disparities and barriers associated with increased overdose rates. This could include social support resources to address economic instability or providing access to harm reduction resources (e.g., naloxone, fentanyl test strips), as well as improving linkage to substance use disorder treatment as part of NFOD follow-up care.

Additionally, it is essential that overdose response strategies address SDOH that contribute to racial and ethnic disparities in NFOD rates. Public health and healthcare providers can work collectively to identify and address systemic inequities in both communities and health systems that contribute to substance use and overdose among racial and ethnic minorities. Interventions could include partnerships with community- and faith-based organizations to develop culturally sensitive messaging and to identify community members to serve as trusted liaisons, helping to destigmatize drug use.

Finally, ongoing surveillance and analysis of community-level risk factors for NFODs as well as associated patient demographic data are needed to drive public health program development and evaluate changes needed as the socioecological characteristics of communities change over time. Public health and clinicians can work together to ensure standardized, complete patient data are collected and reported to inform and evaluate work to decrease overdose rates and minimize disparities.