Sickle cell, thalassemia, and heat: risk estimates and equity policy considerations from an exploratory timeseries study in California

Background: People born with hemoglobinopathies, such as sickle cell disease (SCD) and thalassemia, as well as people who are carriers for these disorders [sickle cell trait (SCT), thalassemia trait or thalassemia minor (TM)], may experience increased symptom-triggers and related illnesses from heat because their cells are susceptible to dehydration. Additionally, historical, and structural injustices could also exacerbate risk vulnerabilities among some communities. Methods: In this work, we (1) present an overview of biological plausibility linking heat and hemoglobinopathy-related hospitalizations; (2) analyze the relationship between daily apparent temperature and such hospitalizations in California using Patient Discharge Data (PDD) and a two-stage timeseries study design with Poisson regression to estimate a state-wide hospitalization risk estimate; (3) discuss how structural barriers working in conjunction with demographic and genetic factors have conferred added risk to some Californians, thereby presenting deep-seeded equity ramifications. Results: Our final dataset, restricted to the warm season, consisted of 96,908 daily counts of any hemoglobinopathy, listed as primary or secondary hospital diagnoses in PDD data. For an overall result, we observed an elevated risk of 3.0% (95% CI: 0.6, 5.5) per 10-degree Fahrenheit (°F) increase in apparent temperature at the last 30-day cumulative exposure window. For secondary hospital diagnoses of SCT-associated outcomes, when limited to very populous areas, we observed an elevated association of 7.0% at lag 23 (95% CI: 2.2, 12.1). Conclusions: We observed excess symptom associations at various heat exposure levels, highlighting the need to examine longer exposure periods and potential care delays (stigma, medical racism, healthcare access). Differences and uncertainties could also stem from other comorbidities, age, genetics, housing and socioeconomic characteristics, or lifestyle variations. Education on the possible links between climate and hemoglobinopathy symptoms, changing demographics, and long overdue research funding may help close the gap in this interconnecting, critical environmental justice issue.