Seasonal and meteorological determinants of aneurysmal subarachnoid hemorrhage: a systematic review and meta-analysis

Abstract

Many studies have assessed the relationships between seasonal or meteorological determinants and the occurrence of aneurysmal subarachnoid hemorrhage (SAH), but the data are conflicting. We systematically searched the literature and meta-analyzed data from all relevant articles when possible. We searched MEDLINE (1966-2011), EMBASE (1980-2011) and the Cochrane Library to identify all observational studies examining the relationship between seasonal and meteorological determinants (temperature, atmospheric pressure and relative humidity) and the occurrence of SAH. Two authors independently extracted data from articles that were included based on predefined criteria. We pooled relative risks (RR's) with corresponding 95 % confidence intervals (CI's) from the individual studies on season and month by means of the random effects method. We included 48 articles, totaling 72,694 patients. SAH occurred less often in summer than in winter (RR 0.89, 95 % CI 0.83-0.96), and was statistically significant more often in January than in the summer months of June-September. For atmospheric pressure seven of 17 studies found a significant association, six of 18 studies were significant for temperature, and three of 15 studies were significant for humidity, but the direction of these associations was conflicting and data on these determinants were too heterogeneous to pool. Seasons influence the occurrence of SAH, with SAH occurring less often in summer than in winter, and most often in January. The explanation for the seasonal differences remains uncertain, due to the lack of sound data on the influence of meteorological factors on SAH occurrence.

Seasonal variation in hemorrhage and focal neurologic deficit due to intracerebral cavernous malformations

“…Seasonal variation has been studied in many neurologic conditions with mixed and often conflicting results [9][10][11]. In addition, explanations for the seasonal variation are often lacking.…”

Increased incidence of subarachnoid hemorrhage during cold temperatures and influenza epidemics

“…10,13,16,22,32,36 These conflicting results may be explained by referral bias or lack of power due to small sample size in single-center or small regional studies, a limited study period, or variety in study definitions (i.e., mean/ maximum/minimum temperature, temperature difference, season, or wind chill). The evidence on recent infection in relation to the incidence of SAH is limited.…”

Associations between Temperature and Hospital Admissions for Subarachnoid Hemorrhage in Korea

“…For example, Piters et al [19] found a higher occurrence of SAH in January than in the summer months of June–September. In a retrospective study of SAH admissions in the Mid-Atlantic region of the United States, Gill et al [12] found a statistically significant increase in SAH when a decrease in temperature occurred within a 24-h period.…”

“…However, whether or not seasonal or meteorological factors influence SAH is still a matter of debate. Based on a systematic review and meta-analysis, Piters et al [19] observed that SAH occurs less often in summer than in winter, and most often in January. However, other studies failed to show any seasonal or meteorological associations [20,21,22].…”