Environmental exposures resulting from climate change, such as extreme heat, often overlap with social determinants of poorer health. These include geographical factors (e.g., living closer to toxins or heat islands, or having poor access to health facilities) and structural conditions (e.g., racism and income inequality) that prevent equal access to opportunities such as education and employment.
In the first study of its kind, Leah Santacroce, MS, a programmer analyst in the Division of Rheumatology, Inflammation and Immunity at Brigham and Women’s Hospital, Paul F. Dellaripa, MD, and Candace H. Feldman, MD, MPH, ScD, rheumatologists in the division, and colleagues showed individuals with rheumatic conditions residing in neighborhoods with high social or heat vulnerability have greater odds of recurrent hospitalization than people in areas with lower vulnerability. They published their results in Arthritis Care & Research.
The study subjects were 14,401 adults who were treated at a Mass General Brigham-affiliated hospital rheumatology clinic for a systemic rheumatic condition, crystalline arthritis, or osteoarthritis between January 1, 2010, and April 28, 2021.
The primary exposures studied were:
- The Social Vulnerability Index (SVI), which was developed by the CDC and the Agency for Toxic Substances and Disease Registry. Based on U.S. Census tract–level data for 15 variables, the index assesses how susceptible a neighborhood is to hazardous events and how readily a community can mobilize to prevent adverse effects from those events.
- The Heat Vulnerability Index (HVI) for the Metro Boston area was developed by the Metropolitan Area Planning Council to show how the adverse effects of heat disproportionately affect certain populations living in and around the city.
The study’s primary outcome was hospitalization at a Mass General Brigham-affiliated hospital over a two year period. The frequency of hospitalization was classified as 0, 1–3, or ≥4 visits.
Key results about social vulnerability and hospitalization were:
- Individuals living in areas with the highest social vulnerability had 84% greater odds of ≥4 hospitalizations than individuals living in the least vulnerable areas, even after adjustment for individual-level demographics, insurance status, and the Deyo–Charlson Comorbidity Index
- A “dose-dependent” association was evident, with higher odds of repeated hospitalizations accompanying higher categories of social vulnerability
- Black individuals had 50% higher odds of ≥4 hospitalizations than white individuals after adjustment for neighborhood social vulnerability, and during the warmer months of May to September, the odds were more than two times higher
- Publicly insured individuals (both Medicaid and Medicare beneficiaries) had significantly higher odds of 1–3 and ≥4 hospitalizations than commercially insured individuals
10,862 of the study subjects were living in the Metro Boston area. Key results about their heat vulnerability and hospitalization were:
- Individuals living in areas with the highest heat vulnerability had a statistically significant 64% higher odds of ≥4 hospitalizations than people in the least vulnerable areas
- During the warmer months, findings were similar and statistically significant for 1–3 hospitalizations among individuals living in areas rated in the highest two (of four) categories of heat vulnerability
Results by Individual Disease
Associations between social and heat vulnerability and recurrent hospitalizations were stronger among individuals with systemic rheumatic conditions and crystalline arthritis than among those with osteoarthritis.
New Directions for Research
The effects of climate change are expected to become more frequent and severe. It’s imperative to determine which populations of patients with rheumatic conditions are at the greatest risk of avoidable adverse events from extreme heat and other climate-related harms, such as flooding. Scientists also need to uncover the mechanisms contributing to differences in hospitalization risk according to the type of rheumatic disease.