Short-Term Extreme Temperatures, Temperature Fluctuations, and the Risk of Aneurysmal Subarachnoid Hemorrhage: A Nationwide Case-Crossover Study

BACKGROUND: Previous studies have shown inconsistent links between seasonal variation or ambient temperature and aneurysmal subarachnoid hemorrhage (aSAH) onset. Furthermore, the impact of short-term temperature fluctuations on aSAH remains unclear. This study aims to quantify the exposure-response relationship between short-term extreme temperatures or temperature fluctuations and aSAH risk. METHODS: This time-stratified case-crossover study used a multicenter registry database (May 1, 2017, to December 31, 2022) from 33 tertiary hospitals in China, including 6004 consecutive aSAH cases with onset dates and residential addresses. Exposures were short-term extreme temperatures and temperature fluctuations (diurnal temperature range and temperature change between neighboring days) lagging up to 6 days before onset. Main outcomes were analyzed using conditional logistic regression with a distributed lag nonlinear model to assess associations between aSAH onset and daily mean ambient temperature, diurnal temperature range, and temperature change between neighboring days. Subgroup, sensitivity, and attributable analyses were also performed. RESULTS: The final analysis included 5842 patients with aSAH (mean age, 57.1±11.6 years; 61.9% women). Higher or lower daily mean ambient temperature (95% CI, ≤6.6 °C or ≥21.3 °C), higher diurnal temperature range (95% CI, ≥14.1 °C), and larger absolute values of temperature change between neighboring days (95% CI, ≤−2.1 °C or ≥0.8 °C) were associated with an increased risk of aSAH, with effects lasting 3 days for them. Hypertension ( P =0.018; odds ratio, 3.78 [95% CI, 1.85–7.74]) and low annual income ( P =0.033; odds ratio, 3.45 [95% CI, 1.80–6.60]) were significantly associated with increased aSAH risk under low daily mean ambient temperature condition; furthermore, the odds ratios associated with extreme temperature exhibited higher trends for patients who aged ≥65 years or lived in northern China. CONCLUSIONS: In this nationwide, case-crossover study, exposure-response relationships of higher risks of aSAH onset with short-term extreme temperatures and temperature fluctuations were identified, especially for high-risk populations, indicating the need for tailored prevention strategies. REGISTRATION: URL: https://www.clinicaltrials.gov ; Unique identifier: NCT03115905.