Relationship Of Aneurysmal Subarachnoid Haemorrhage And Climatic Conditions: A Retrospective Population-Based Study
E Shenouda, L Pobereskin
climate, population - based study, subarachnoid haemorrhage
E Shenouda, L Pobereskin. Relationship Of Aneurysmal Subarachnoid Haemorrhage And Climatic Conditions: A Retrospective Population-Based Study. The Internet Journal of Neurosurgery. 2004 Volume 2 Number 2.
The objective of this study was to investigate the relationship between climatic conditions and aneurysmal subarachnoid haemorrhage (SAH).
All patients with a diagnosis of SAH in the years 1992 - 1996 were identified. Data on these patients were obtained from a retrospective population-based study. Days with and without incidents were compared with data obtained from the Met Office; hourly barometric pressure changes, temperature, and humidity. Groups were compared with student's t test and the
2 test for continuous variables and proportions respectively.
Eight hundred cases of SAH were identified in the time period studied. There were 516 (64%) women and 284 men. The mean age at diagnosis was 61 (SD ± 15) years. Forty six percent of patients were over 65 years of age. SAH was more likely to occur on days with higher barometric pressure (P 0.031) however; the actual pressure differences were negligible. There was no relationship between temperature, humidity, and SAH. There was no seasonal variation in the incidence of SAH. There was no association between the severity of SAH and climatic conditions or the day of the week. SAH is less likely to occur over the weekend particularly Saturday 0.735 (0.611-0.885), (relative risk (95% confidence interval). SAH was more likely to occur on Tuesday with a relative risk of 1.153 (1.001 - 1.327).
There is a statistically significant relationship between SAH and barometric pressure but not with either temperature or humidity. The day of the week does influence the incidence of SAH. The underlying reasons remain uncertain.
Hippocrates (460-370 BC) observed that apoplexy was more common in rainy weather and in winter (2). This observation has prompted many researchers to investigate the relationship between the occurrence of stroke and climate changes. There have been many anecdotal reports of patients presenting with SAH and other cerebrovascular disorders particularly after abrupt changes in weather (8, 19, 22, 24, 31, 33, 39). However, all these studies were based on hospitalised patients and mortality statistics. Little is known about the relationship of climate changes and SAH among the general population (36). At our institution, a retrospectively acquired population-based database of all patients with SAH has been obtained for the years between 1992 and 1996. Using this data and the local atmospheric pressure, temperature, and humidity readings obtained from the Met Office, we have investigated the relationship between SAH and climate changes in the population of two English counties. Our hypothesis was that a rise in the incidence of aneurysmal SAH occurs when the weather conditions change, especially atmospheric pressure.
Ethical approval was obtained from the south and west Devon Health Authority ethics committee.
The two counties of Devon and Cornwall have an area of 10 347.4 Km2. The population in 1992 (1991 United Kingdom census) was 1 475 634 and in 1996 (midcensus estimate, Office of National Statistics (ONS)) it was 1 504 847, an increase of less than 2%. The population is overwhelmingly white (99.27%) (1991 United Kingdom census) The study area is isolated on a peninsula and is served by five district general hospitals and one tertiary referral centre for Neurosurgery. During the study period there was a CT unit at each of the hospitals in the two counties. A modern ambulance service, as well as two helicopters, operated in the study area.
Patients with sudden neurological catastrophe were first taken to the nearest hospital where they were stabilized and scanned. All tertiary care was provided at the Neurosurgery department at Plymouth.
Meteorological data were obtained from three different stations in the peninsula. These included daily statements of three variables, barometric pressure, temperature, and humidity. Each variable was provided in four readings; minimum, maximum, difference, and mean.
We compared days with and without incidents with data obtained from the Meteorological office; barometric pressure changes, temperature, and humidity. Groups were compared with Student's
Data handling was performed using Microsoft Access V 7.0 and analysis carried out with SPSS V 8.0 on a personal computer.
The details of case ascertainment can be found in our previous study (30). Briefly, a total of 901 medical records were reviewed. Cases were excluded for the following reasons: arteriovenous malformation (24), primary head injury (18), previous subarachnoid haemorrhage (13), primary intracerebral haemorrhage (10), and lack of verification by CT, lumbar puncture, or necropsy (five). The medical records of 31 patients could not be found. Eight hundred cases of first ever subarachnoid haemorrhage were identified during the 5-year study period. Computerized Tomography (CT) verified subarachnoid haemorrhage in 609 (77%) patients, autopsy in 181 (22%), and a typical history and lumbar puncture in 10 (1%).
There were 516 (64%) women and 284 men. The mean age at diagnosis of the cohort was 61 (SD 15) years. Women were significantly older than men (p<0.0005). The mean age for women was 63 (range 11-96) years and for men it was 57 (19 - 91) years. Forty six percent of patients were over 65 years of age.
There were 1827 days during the study period. There were 800 events during this period and 106 days had two events, 20 days had 3 events and on one day 4 events occurred. In total, an event occurred on 651 of the days in the study period.
Comparing the days on which SAH occurred with days free of incidents, we noted that barometric pressure on days with SAH (mean value = 1016.95 Mb) was higher than on days without (1015.87 Mb) (P= 0.031).
Air temperature and relative humidity
There was no significant relationship between humidity and temperature and the occurrence of SAH. This was true for comparisons of minimum, maximum and range of both variables. The results were the same when subgroup analysis was performed based on age and gender.
Severity of SAH
Patients with severe SAH were defined as those who died within 30 days (45%). We found no association between climactic conditions or day of the week and the severity of SAH.
Seasonal variations in the occurrence of aneurysmal SAH, stratified by sex are shown in Figure 1. In males there was a tendency for the incidence of SAH to fall from winter to autumn but this was not statistically significant. For females the percent of days with events was constant across the seasons.
Day of the week
The distribution of SAH onset across the day of the week is shown in Figure 2.
This retrospective population-based study suggests that the risk of SAH increases with atmospheric pressure. This agrees with previously published reports looking at either cerebrovascular accident in general or SAH in particular. Madzhibov
Attempts to relate the occurrence of stroke in general or SAH in particular to climatic conditions have usually considered not only atmospheric pressure changes but also, atmospheric temperature (1,2,6,7,12,34,36,38,40,44), and humidity (4,6,7,12,40). Chyatte
Seasonal variations in the incidence of SAH have been investigated in many previous studies (1,2,8,9,15,16,17,18, 19,21,26,27,28,32,.33,34,35,36,37, 38,40,42). However, there is still a considerable debate over this issue. Studies that have demonstrated significant seasonal variation in SAH have all been hospital-based (8,9,15,19,24,27,28,33,40,42). This is not surprising as the use of hospital based data to study seasonal variations of SAH occurrence is prone to bias because it does not include a substantial proportion (~15%) of patients who die from SAH before reaching the hospital (10,35) However, no statistically significant seasonal variation was observed in any of the population-based studies (16,17,18,21,32,34,35,36,38) but one (10). Feigin
There are only a few reports in the literature which have examined the possible relationship between day of the week and stroke (3, 10, 14, 20, 21, 24, 29, 41). Feigin
In conclusion, we found a statistically significant relationship between SAH and barometric pressure but not with either temperature or humidity. The day of the week does influence the incidence of SAH. However, there is obvious inconsistency in weather data and SAH in the literature. Publication bias may explain these apparent inconsistencies as negative data tend not to be published; the preponderance of published data supports some kind of association between weather and SAH (13). Further prospective epidemiological and physiological studies are warranted to clarify the influence of weather on SAH.
We wish to express special thanks to Met Office team in Devon and Cornwall for providing the climate data.
Mr Emad Shenouda Department of Neurosurgery Frenchay Hospital Bristol BS16 1LE, UK E-mail: email@example.com