Falling Temperature and Colder Weather Are Associated with an Increased Risk of Aneurysmal Subarachnoid Hemorrhage

OBJECTIVE: To use weather data to predict increased incidence of aneurysmal subarachnoid hemorrhage (aSAH) at a large institution with an extensive referral network in response to falling temperatures. METHODS: In a retrospective study, 1175 prospectively collected aSAH cases accrued over 18 years from one hospital were reviewed to determine if season, maximum ambient temperature (MAT), average relative humidity, and atmospheric pressure were related to incidence of aSAH at that institution on a given day. A Poisson regression model was used to assess daily risk of incident aSAH based on daily MAT and 1-day change in MAT. RESULTS: A MAT decrease of 1 degrees F from one day to the next was associated with a 0.6% increase in risk of aSAH (relative risk [RR] = 1.006, P = 0.016). The increased risk associated with MAT decrease from the previous day was especially strong for female patients (RR = 1.008/degrees F, P = 0.007) and drove the overall model, representing 72% of cases. In addition, warmer temperatures were associated with a decreased risk of aSAH; each 1 degrees F increase in temperature compared with the previous day was associated with a 0.3% decrease in risk of aSAH (RR = 0.997; P < 0.001). CONCLUSIONS: A 1-day decrease in temperature and colder daily temperatures were associated with an increased risk of incident aSAH at a single institution with a large referral network. These variables appeared to act synergistically and independently of season. These relationships were particularly predominant in the fall when the transition from warmer to colder temperatures occurred.