Original Article
Ambient air pollution, weather and daily emergency department visits for headache
Cephalalgia 2015, Vol. 35(12) 1085–1091 ! International Headache Society 2015 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0333102415570300 cep.sagepub.com
Alina Vodonos1,2, Victor Novack2, Yair Zlotnik3 and Gal Ifergane3 Abstract Background: Headache is a common condition, and a common complaint leading patients to emergency departments (ED). There have been a number of studies of the effect of environmental factors on headache, such as weather and air pollutants. Methods: This retrospective cohort study included data on daily ED visits with a chief complaint of headache in Soroka University Medical Center (SUMC) during 2002–2012. Data on weather and air pollutants were obtained from monitor station in Be’er-Sheva. To estimate the short-term effects of air pollution and temperature on number of daily headache ED visits, we applied generalized linear mixed models (GLMM). Results: A total of 22,021 ED visits were included in the analysis. An increase in 5 C in temperature was associated with an increase in ED visits, relative risk (RR) ¼ 1.042, (95% CI 1.009; 1.076). RR for headache was associated with an increase in 10 units of nitrogen dioxide (NO2), RR ¼ 1.110 (95% CI 1.057; 1.167), with a higher effect for older patients. Discussion: The current findings give evidence of an association between air pollution, weather and ED visits for headache, especially for NO2. Short-term increases in air pollution exposure may trigger headache by increasing pulmonary and systemic inflammation, increasing blood coagulability or altering endothelial function. Keywords Dust exposure, air pollution, headache, emergency department visit Date received: 9 September 2014; revised: 23 October 2014; accepted: 6 December 2014
Introduction Acute headache is a common condition, and a common presenting complaint in patients at emergency departments (ED). It is estimated that 1%–3% of all ED visits are due to non-traumatic headache (1). Intracranial pathology is found in only a small minority of these patients (3.5%–10.1%) (2) and most of them suffer from primary headache disorders. Research directed at identifying precipitating factors for headache episodes in both disorders (commonly referred to as ‘‘triggers’’) identified several potential factors such as: menstrual changes, afferent stimulation, physical activity, psychological factors, sleep disorders, dietary factors and multiple environmental factors, such as weather, noise, electromagnetic fields, environmental lighting, visual stimuli, odors, cigarette smoke and air pollutants (3–8).
There have been a number of studies examining the effect air pollution on headache (9,10). Szyszkowicz (11) examined 8012 ED visits for headache recorded in Ottawa. This analysis revealed that ED visits for headache are associated with an increased concentration of anthropogenic air pollutants (sulfur dioxide (SO2), nitrogen dioxide (NO2) and carbon monoxide (CO)).
1 Public Health Department, Faculty for Health Sciences, Ben-Gurion University of the Negev, Israel 2 Clinical Research Center, Soroka University Medical Center, Israel 3 Neurology Department, Soroka University Medical Center, Israel
Corresponding author: A Vodonos, Clinical Research Center, Soroka University Medical Center, P.O.B. 151, Be’er-Sheva, Israel. Emails: [email protected]; [email protected]
1086 In this study, we investigated the role of meteorological parameters and air pollutants as headache triggers in the hot and arid geographic region of southern Israel.
Materials and methods Study population We obtained data on daily ED visits to Soroka University Medical Center (SUMC) with a primary complaint of headache in patients 18 years or older during the 10-year period (between December 1, 2002 and December 31, 2011). SUMC is a tertiary 1000-bed hospital and the only medical center area serving a population of 700,000 of Southern Negev. The annual adult ED visits volume is 100,000. We excluded from the analysis all cases that were hospitalized following the ED visit. The analyses for air pollution were restricted only to the residents of Be’er-Sheva (main city in the region, population 215,000), where data from monitor stations were available. The analyses for meteorological factors were analyzed for residents of all of the southern Negev.
Environmental data Data on meteorological parameters (temperature and relative humidity) and air pollutants were obtained from the monitoring station in Be’er-Sheva operated by the Ministry of Environmental Protection. This is the only monitoring station in the area, which measures all pollutants simultaneously in 20-minute intervals. Historical data for the entire study period include particles with median aerodynamic diameter of 10 mm or less (PM10) concentrations (mg/m3) over time along with NO2 (parts per billion (ppb)) and SO2 (ppb) and average, minimum and maximum temperature ( C). Seasons were defined according to the Alpert et al. synoptic definition (12), where winter and the summer each last approximately four months (three months and 23 days), and the autumn and spring each last nearly a half of this period, 75 days and 61 days, respectively. Desertification and global warming trends pose significant global ecological and environmental problems (13); e.g. land degradation processes resulting in increasing exposure of population to dust sources in arid and semiarid soils and possible dust storms (14). The Negev region is located between the Saharan and the Arabian deserts (the world’s largest dust belt) and every year is exposed to several intensive dust storms (15,16). A dust-storm (DS) day was defined as a day with an averaged PM10 concentration that was two standard deviations (SD) above the background value and was equal to 71 mg/m3 (16).
Cephalalgia 35(12)
Statistical analysis Data were summarized using frequency tables for categorical variables and summary statistics (mean with SD) for continuous variables. To estimate the shortterm effects of air pollution and temperature on number of daily headache ED visits, we applied a generalized linear mixed models (GLMM) methodology described by Szyszkowicz (17). This technique is based on Poisson regression applied to clustered counts. Poisson random-effects models were applied to analyze the cluster counts where the groups of days, determined by the triplet (day of the week, month, year), form the clusters. The hierarchical construction of the clusters allows the model to incorporate level-specific random effects. The behavior of an individual is associated with this hierarchical structure and by consequence many health outcomes are cluster dependent. We used the glmmPQL function from the R statistical package to perform the analysis (17). Relative risk (RR) with 95% confidence intervals (CIs) represent the risk of ED visits for headache associated with an increase in average of pollutant concentration. Each pollutant (PM10, NO2 and SO2) was examined in a separate model, adjusted for temperature and relative humidity. The dust-storm variable was treated as a dichotomous yes/no variable based on occurrence on a given day. For testing possible nonlinear association with temperature variable, we used penalized splines with five degrees of freedom. Additionally, we stratified our analysis by gender and by season (summer, fall, winter and spring). P values less than 0.05 were considered statistically significant.
Results The study population comprised 18,065 patients with 22,021 visits, thus 18% of the patients had more than one visit during the study period. Among them, 42.5% were residents of Be’er-Sheva, 56.6% were female and 59.9% were younger than 40 years old (Table 1). During the weekends, there was a significantly lower Table 1. Frequency of emergency department (ED) visits for headache. Number of ED visits (%) Age (years) 60 Gender Male Residents of Be’er-Sheva Total number of headache ED visits
13,194 (59.9%) 6,019 (27.3%) 3,362 (15.3%) 9,556 (43.3%) 9,354 (42.5%) 22,021
1087
Vodonos et al. Table 2. Mean, SD of daily levels of air pollutants, meteorological factors and daily numbers of ED visits for headache. Variable (unit), mean SD
All seasons
Summer (May 31–Sep 22)
Autumn (Sep 23–Dec 6)
Winter (Dec 7–Mar 30)
Spring (Mar 31–May 30)
Meteorological factors Temperature ( C) Minimum temperature ( C) Maximum temperature ( C) Humidity (%)
20.3 5.9 14.7 5.6 26.8 7.1 67.9 16.0
26.5 1.9 20.4 2.6 33.5 2.9 70.5 10.5
20.5 3.9 15.2 4.7 26.9 3.9 66.9 16.9
13.7 3.3 8.8 4.8 19.7 2.7 69.7 18.5
20.7 3.7 14.3 5.1 27.8 3.3 61.4 16.6
Air pollutants PM10 (mg/m3) NO2 (ppb) SO2 (ppb)
56.5 95.5 9.9 5.0 1.9 0.8
41.9 17.5 7.3 2.7 1.5 0.7
50.7 43.5 12.1 5.1 1.9 0.9
70.9 142.6 12.1 5.9 2.1 0.8
64.3 114.5 8.5 3.4 2.0 0.7
5.4 2.6 4.0 1.9 0.3 0.5 2.3 1.6
5.4 2.6 3.9 2.0 0.3 0.5 2.2 1.6
5.4 2.7 4.0 2.0 0.3 0.5 2.3 1.6
5.5 2.6 4.0 1.9 0.3 0.5 2.3 1.6
5.3 2.5 4.0 2.0 0.3 0.5 2.4 1.6
Daily ED visits All Weekday Weekend Residents of Be’er-Sheva
Effect of temperature on the incidence of headache ED visits A positive association was found between an increase in five units of temperature in C and incidence of ED visits for headache (Figure 1): For all cases, RR (1.042, 95% CI 1.009; 1.076, p ¼ 0.005), for the fall seasons, RR (1.052, 95% CI 1.004; 1.102, p ¼ 0.034) and winter season, RR (1.063, 95% CI 1.034; 1.125, p ¼ 0.038) (Figure 2). Higher associations were observed one day after the exposure during the fall and winter seasons only, RR (1.063, 95%CI 1.015; 1.114, p ¼ 0.010) and RR (1.084, 95% CI 1.023; 1.148, p ¼ 0.006).
0.4 0.2 0.0 – 0.2 – 0.4 – 0.6
number of daily headache ED visits (5.9 2.6 vs. 4.1 2.1, p < 0.001). The distribution of the daily 24-hour average concentrations of PM10, NO2, SO2 and daily meteorological factors are presented in Table 2. For 1041 (26.1%) days of the study period, the PM10 levels exceeded the World Health Organization (WHO) recommended daily guideline of 50 mg/m3 (18). We have identified 469 (12.8%) dust-storm days during the study period based on our calculated value (71 mg/m3) with the majority occurring during the winter and spring seasons (from December to May). The average daily temperature was 20.3 5.9 C, reaching a maximal temperature of 42.4 7.1 C. Variability of daily number of headache ED visits by season was small: 5.4 2.6, 5.4 2.7, 5.5 2.6 and 5.3 2.6 for summer, autumn, winter and spring, respectively.
Change in number of daily headache ED visits
Study period: January 1, 2002–December 31, 2011. CO: carbon monoxide; ED: emergency department; IQR: interquartile range; NO2 ¼ nitrogen dioxide; SO2 ¼ sulfur dioxide; PM10 ¼ particles with median aerodynamic diameter of 10 mm or less; ppb: parts per billion.
5
10
15 20 Temperature (C°)
25
Figure 1. Change in number of daily emergency department (ED) visits for headache associated with daily average temperature ( C).
Effect of anthropogenic air pollution on the incidence of headache ED visits The association between air pollution and incidence of headache in the city of Be’er-Sheva by pollutant and
RR
1.300 1.200 1.100 1.000 0.900 0.800 0.700 0.600
RR
1.062 1.044 1.026 1.008 0.990 0.972 0.954
Temperature (C°)
1.023
Summer
1.013 Spring
1.063
Winter
1.052
Fall
1.042
Figure 2. The effect of short-term increase in temperature on emergency department (ED) visits for headache, by season. Relative risk (RR) and 95% confidence interval for ED visits per 5 C increase in daily temperature concentrations. Results of the separated Poisson regression models, for study period 2002–2012 (N ¼ 22,021 ED visits), adjusted for temperature and relative humidity in all and divided by season.
season is presented in Figure 3. The strongest effect was observed between an increase in NO2 (10 units) and headache visits incidence. For all cases the RR for headache visit on the same day was 1.11 (95% CI 1.057; 1.167, p < 0.001). Analysis stratified by season revealed that ED visits for headache were significantly associated with increase in 10 units of NO2 in the winter and spring seasons (RR ¼ 1.18, 95% CI 1.45; 1.19, p ¼ 0.001 and RR ¼ 1.32 (95% CI 1.12; 1.56, p ¼ 0.001 respectively), but not during the summer and fall, respectively.
Effect of particulate matter air pollution on the incidence of headache ED visits An association between PM10 and ED visits on the same day was found during the fall season, RR for increase in 10 units of PM10 ¼ 1.01(95% CI 1.00; 1.02, p ¼ 0.006). This association was immediate and did not remain the day after the exposure. No significant association between dust-storm days and ED visits was found, but a positive association was shown during the winter and fall season.
Associations for ED visits for age and gender groups The analysis of association between temperature and ED visits stratified by gender did not reveal any significant effect: RR for increase in five units of temperature in C in women ¼ 1.052 (95% CI 0.981; 1.123, p ¼ 0.081) and men, RR ¼ 1.014 (95% CI 0.991; 1.037, p ¼ 0.241). Similarly, the effect of temperature on headache ED visits did not increase with age. On the contrary, analysis stratified by age and gender for association with air pollutants (Table 3) showed that older patients (above 60) were at higher risk for headache ED visits associated with dust-storm exposure compared to younger patients (age 40–60 and younger
Dust Storm 0.978
Summer
All
1.480
1.048 0.936
Spring
Winter
1.011
Fall
0.997
All
PM10 1.020
1.014 1.000
Summer 1.650
RR
1.600 1.500 1.400 1.300 1.200 1.100 1.000 0.900 0.800
Cephalalgia 35(12)
Spring
0.998
Winter
Fall
1.000
All
NO2 1.321
1.310 1.140
1.118
1.085
1.119
1.111
0.970 0.800 Spring 2.300
Winter
Fall
Summer
All
SO2
1.800 1.620 RR
RR
1088
1.357
1.300
1.246
1.249 0.883
0.800 0.300 Spring
Winter
Fall
Summer
All
Figure 3. The effect of short-term increase in pollutant concentrations on emergency department (ED) visits for headache, by season. Relative risk (RR) and 95% confidence interval for ED visits per 10 units increase in the daily pollutants concentrations. Results of the separated Poisson regression models, for study period 2002– 2012 (N ¼ 9354 ED visits), adjusted for temperature and relative humidity in all and divided by season. NO2 ¼ nitrogen dioxide; SO2 ¼ sulfur dioxide; PM10 ¼ particles with median aerodynamic diameter of 10 mm or less.
than 40); RR ¼ 1.132 (95% CI 1.014; 1.265, p ¼ 0.028), RR ¼ 1.075 (95% CI 0.985; 1.174, p ¼ 0.106) and RR ¼ 1.003 (95% CI 0.943; 1.066, p ¼ 0.935), respectively. The effect of NO2 also increased with age: RR ¼ 1.141 (95% CI 1.049; 1.241, p ¼ 0.002) for the group age 40–60 compared to the younger patients; RR ¼ 1.057 (95% CI 0.989; 1.131, p ¼ 0.105).
Discussion In this analysis of more than 22,000 visits with headache to the ED, we have assessed the short-term effects of meteorological and air pollution factors. We have found that an increase in temperature and NO2 was associated with increased risk of headache ED visits. This effect of the ambient temperature was particularly evident during colder seasons (winter and fall). The effect of NO2 and dust storm increased with age.
1089
Vodonos et al.
Table 3. Relative risk of headache emergency department (ED) visits associated with increase in pollutant concentrations by age, gender.
Category Gender Male Female Age groups Age 60
Dust storm
PM10 (mg/m3)
NO2 (ppb)
SO2 (ppb)
RR
95% CI
RR
95% CI
RR
95% CI
RR
95% CI
0.980 1.046
0.878 0.962
1.095 1.138
1.002 1.000
0.998 0.997
1.005 1.003
1.100 1.121
1.020 1.058
1.186 1.188
1.290 1.108
0.804 0.770
2.068 1.595
1.003 1.075 1.132
0.943 0.985 1.014
1.066 1.174 1.265
1.000 1.001 1.002
0.997 0.997 0.996
1.003 1.005 1.007
1.057 1.141 1.063
0.989 1.049 0.975
1.131 1.241 1.160
1.050 1.577 1.403
0.687 0.925 0.723
1.606 2.690 2.720
Relative risk (RR) and 95% confidence interval (CI) for ED visits per 10 units increase in the daily pollutants concentrations. Results of the separated Poisson regression models for study period 2002–2012 (N ¼ 9354 ED visits), adjusted for temperature and relative humidity in all and divided by season. NO2 ¼ nitrogen dioxide; SO2 ¼ sulfur dioxide; PM10 ¼ particles with median aerodynamic diameter of 10 mm or less; ppb: parts per billion. Boldface indicates positive statistical significant results (p-value
Ambient air pollution, weather and daily emergency department visits for headache
Cephalalgia 2015, Vol. 35(12) 1085–1091 ! International Headache Society 2015 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0333102415570300 cep.sagepub.com
Alina Vodonos1,2, Victor Novack2, Yair Zlotnik3 and Gal Ifergane3 Abstract Background: Headache is a common condition, and a common complaint leading patients to emergency departments (ED). There have been a number of studies of the effect of environmental factors on headache, such as weather and air pollutants. Methods: This retrospective cohort study included data on daily ED visits with a chief complaint of headache in Soroka University Medical Center (SUMC) during 2002–2012. Data on weather and air pollutants were obtained from monitor station in Be’er-Sheva. To estimate the short-term effects of air pollution and temperature on number of daily headache ED visits, we applied generalized linear mixed models (GLMM). Results: A total of 22,021 ED visits were included in the analysis. An increase in 5 C in temperature was associated with an increase in ED visits, relative risk (RR) ¼ 1.042, (95% CI 1.009; 1.076). RR for headache was associated with an increase in 10 units of nitrogen dioxide (NO2), RR ¼ 1.110 (95% CI 1.057; 1.167), with a higher effect for older patients. Discussion: The current findings give evidence of an association between air pollution, weather and ED visits for headache, especially for NO2. Short-term increases in air pollution exposure may trigger headache by increasing pulmonary and systemic inflammation, increasing blood coagulability or altering endothelial function. Keywords Dust exposure, air pollution, headache, emergency department visit Date received: 9 September 2014; revised: 23 October 2014; accepted: 6 December 2014
Introduction Acute headache is a common condition, and a common presenting complaint in patients at emergency departments (ED). It is estimated that 1%–3% of all ED visits are due to non-traumatic headache (1). Intracranial pathology is found in only a small minority of these patients (3.5%–10.1%) (2) and most of them suffer from primary headache disorders. Research directed at identifying precipitating factors for headache episodes in both disorders (commonly referred to as ‘‘triggers’’) identified several potential factors such as: menstrual changes, afferent stimulation, physical activity, psychological factors, sleep disorders, dietary factors and multiple environmental factors, such as weather, noise, electromagnetic fields, environmental lighting, visual stimuli, odors, cigarette smoke and air pollutants (3–8).
There have been a number of studies examining the effect air pollution on headache (9,10). Szyszkowicz (11) examined 8012 ED visits for headache recorded in Ottawa. This analysis revealed that ED visits for headache are associated with an increased concentration of anthropogenic air pollutants (sulfur dioxide (SO2), nitrogen dioxide (NO2) and carbon monoxide (CO)).
1 Public Health Department, Faculty for Health Sciences, Ben-Gurion University of the Negev, Israel 2 Clinical Research Center, Soroka University Medical Center, Israel 3 Neurology Department, Soroka University Medical Center, Israel
Corresponding author: A Vodonos, Clinical Research Center, Soroka University Medical Center, P.O.B. 151, Be’er-Sheva, Israel. Emails: [email protected]; [email protected]
1086 In this study, we investigated the role of meteorological parameters and air pollutants as headache triggers in the hot and arid geographic region of southern Israel.
Materials and methods Study population We obtained data on daily ED visits to Soroka University Medical Center (SUMC) with a primary complaint of headache in patients 18 years or older during the 10-year period (between December 1, 2002 and December 31, 2011). SUMC is a tertiary 1000-bed hospital and the only medical center area serving a population of 700,000 of Southern Negev. The annual adult ED visits volume is 100,000. We excluded from the analysis all cases that were hospitalized following the ED visit. The analyses for air pollution were restricted only to the residents of Be’er-Sheva (main city in the region, population 215,000), where data from monitor stations were available. The analyses for meteorological factors were analyzed for residents of all of the southern Negev.
Environmental data Data on meteorological parameters (temperature and relative humidity) and air pollutants were obtained from the monitoring station in Be’er-Sheva operated by the Ministry of Environmental Protection. This is the only monitoring station in the area, which measures all pollutants simultaneously in 20-minute intervals. Historical data for the entire study period include particles with median aerodynamic diameter of 10 mm or less (PM10) concentrations (mg/m3) over time along with NO2 (parts per billion (ppb)) and SO2 (ppb) and average, minimum and maximum temperature ( C). Seasons were defined according to the Alpert et al. synoptic definition (12), where winter and the summer each last approximately four months (three months and 23 days), and the autumn and spring each last nearly a half of this period, 75 days and 61 days, respectively. Desertification and global warming trends pose significant global ecological and environmental problems (13); e.g. land degradation processes resulting in increasing exposure of population to dust sources in arid and semiarid soils and possible dust storms (14). The Negev region is located between the Saharan and the Arabian deserts (the world’s largest dust belt) and every year is exposed to several intensive dust storms (15,16). A dust-storm (DS) day was defined as a day with an averaged PM10 concentration that was two standard deviations (SD) above the background value and was equal to 71 mg/m3 (16).
Cephalalgia 35(12)
Statistical analysis Data were summarized using frequency tables for categorical variables and summary statistics (mean with SD) for continuous variables. To estimate the shortterm effects of air pollution and temperature on number of daily headache ED visits, we applied a generalized linear mixed models (GLMM) methodology described by Szyszkowicz (17). This technique is based on Poisson regression applied to clustered counts. Poisson random-effects models were applied to analyze the cluster counts where the groups of days, determined by the triplet (day of the week, month, year), form the clusters. The hierarchical construction of the clusters allows the model to incorporate level-specific random effects. The behavior of an individual is associated with this hierarchical structure and by consequence many health outcomes are cluster dependent. We used the glmmPQL function from the R statistical package to perform the analysis (17). Relative risk (RR) with 95% confidence intervals (CIs) represent the risk of ED visits for headache associated with an increase in average of pollutant concentration. Each pollutant (PM10, NO2 and SO2) was examined in a separate model, adjusted for temperature and relative humidity. The dust-storm variable was treated as a dichotomous yes/no variable based on occurrence on a given day. For testing possible nonlinear association with temperature variable, we used penalized splines with five degrees of freedom. Additionally, we stratified our analysis by gender and by season (summer, fall, winter and spring). P values less than 0.05 were considered statistically significant.
Results The study population comprised 18,065 patients with 22,021 visits, thus 18% of the patients had more than one visit during the study period. Among them, 42.5% were residents of Be’er-Sheva, 56.6% were female and 59.9% were younger than 40 years old (Table 1). During the weekends, there was a significantly lower Table 1. Frequency of emergency department (ED) visits for headache. Number of ED visits (%) Age (years) 60 Gender Male Residents of Be’er-Sheva Total number of headache ED visits
13,194 (59.9%) 6,019 (27.3%) 3,362 (15.3%) 9,556 (43.3%) 9,354 (42.5%) 22,021
1087
Vodonos et al. Table 2. Mean, SD of daily levels of air pollutants, meteorological factors and daily numbers of ED visits for headache. Variable (unit), mean SD
All seasons
Summer (May 31–Sep 22)
Autumn (Sep 23–Dec 6)
Winter (Dec 7–Mar 30)
Spring (Mar 31–May 30)
Meteorological factors Temperature ( C) Minimum temperature ( C) Maximum temperature ( C) Humidity (%)
20.3 5.9 14.7 5.6 26.8 7.1 67.9 16.0
26.5 1.9 20.4 2.6 33.5 2.9 70.5 10.5
20.5 3.9 15.2 4.7 26.9 3.9 66.9 16.9
13.7 3.3 8.8 4.8 19.7 2.7 69.7 18.5
20.7 3.7 14.3 5.1 27.8 3.3 61.4 16.6
Air pollutants PM10 (mg/m3) NO2 (ppb) SO2 (ppb)
56.5 95.5 9.9 5.0 1.9 0.8
41.9 17.5 7.3 2.7 1.5 0.7
50.7 43.5 12.1 5.1 1.9 0.9
70.9 142.6 12.1 5.9 2.1 0.8
64.3 114.5 8.5 3.4 2.0 0.7
5.4 2.6 4.0 1.9 0.3 0.5 2.3 1.6
5.4 2.6 3.9 2.0 0.3 0.5 2.2 1.6
5.4 2.7 4.0 2.0 0.3 0.5 2.3 1.6
5.5 2.6 4.0 1.9 0.3 0.5 2.3 1.6
5.3 2.5 4.0 2.0 0.3 0.5 2.4 1.6
Daily ED visits All Weekday Weekend Residents of Be’er-Sheva
Effect of temperature on the incidence of headache ED visits A positive association was found between an increase in five units of temperature in C and incidence of ED visits for headache (Figure 1): For all cases, RR (1.042, 95% CI 1.009; 1.076, p ¼ 0.005), for the fall seasons, RR (1.052, 95% CI 1.004; 1.102, p ¼ 0.034) and winter season, RR (1.063, 95% CI 1.034; 1.125, p ¼ 0.038) (Figure 2). Higher associations were observed one day after the exposure during the fall and winter seasons only, RR (1.063, 95%CI 1.015; 1.114, p ¼ 0.010) and RR (1.084, 95% CI 1.023; 1.148, p ¼ 0.006).
0.4 0.2 0.0 – 0.2 – 0.4 – 0.6
number of daily headache ED visits (5.9 2.6 vs. 4.1 2.1, p < 0.001). The distribution of the daily 24-hour average concentrations of PM10, NO2, SO2 and daily meteorological factors are presented in Table 2. For 1041 (26.1%) days of the study period, the PM10 levels exceeded the World Health Organization (WHO) recommended daily guideline of 50 mg/m3 (18). We have identified 469 (12.8%) dust-storm days during the study period based on our calculated value (71 mg/m3) with the majority occurring during the winter and spring seasons (from December to May). The average daily temperature was 20.3 5.9 C, reaching a maximal temperature of 42.4 7.1 C. Variability of daily number of headache ED visits by season was small: 5.4 2.6, 5.4 2.7, 5.5 2.6 and 5.3 2.6 for summer, autumn, winter and spring, respectively.
Change in number of daily headache ED visits
Study period: January 1, 2002–December 31, 2011. CO: carbon monoxide; ED: emergency department; IQR: interquartile range; NO2 ¼ nitrogen dioxide; SO2 ¼ sulfur dioxide; PM10 ¼ particles with median aerodynamic diameter of 10 mm or less; ppb: parts per billion.
5
10
15 20 Temperature (C°)
25
Figure 1. Change in number of daily emergency department (ED) visits for headache associated with daily average temperature ( C).
Effect of anthropogenic air pollution on the incidence of headache ED visits The association between air pollution and incidence of headache in the city of Be’er-Sheva by pollutant and
RR
1.300 1.200 1.100 1.000 0.900 0.800 0.700 0.600
RR
1.062 1.044 1.026 1.008 0.990 0.972 0.954
Temperature (C°)
1.023
Summer
1.013 Spring
1.063
Winter
1.052
Fall
1.042
Figure 2. The effect of short-term increase in temperature on emergency department (ED) visits for headache, by season. Relative risk (RR) and 95% confidence interval for ED visits per 5 C increase in daily temperature concentrations. Results of the separated Poisson regression models, for study period 2002–2012 (N ¼ 22,021 ED visits), adjusted for temperature and relative humidity in all and divided by season.
season is presented in Figure 3. The strongest effect was observed between an increase in NO2 (10 units) and headache visits incidence. For all cases the RR for headache visit on the same day was 1.11 (95% CI 1.057; 1.167, p < 0.001). Analysis stratified by season revealed that ED visits for headache were significantly associated with increase in 10 units of NO2 in the winter and spring seasons (RR ¼ 1.18, 95% CI 1.45; 1.19, p ¼ 0.001 and RR ¼ 1.32 (95% CI 1.12; 1.56, p ¼ 0.001 respectively), but not during the summer and fall, respectively.
Effect of particulate matter air pollution on the incidence of headache ED visits An association between PM10 and ED visits on the same day was found during the fall season, RR for increase in 10 units of PM10 ¼ 1.01(95% CI 1.00; 1.02, p ¼ 0.006). This association was immediate and did not remain the day after the exposure. No significant association between dust-storm days and ED visits was found, but a positive association was shown during the winter and fall season.
Associations for ED visits for age and gender groups The analysis of association between temperature and ED visits stratified by gender did not reveal any significant effect: RR for increase in five units of temperature in C in women ¼ 1.052 (95% CI 0.981; 1.123, p ¼ 0.081) and men, RR ¼ 1.014 (95% CI 0.991; 1.037, p ¼ 0.241). Similarly, the effect of temperature on headache ED visits did not increase with age. On the contrary, analysis stratified by age and gender for association with air pollutants (Table 3) showed that older patients (above 60) were at higher risk for headache ED visits associated with dust-storm exposure compared to younger patients (age 40–60 and younger
Dust Storm 0.978
Summer
All
1.480
1.048 0.936
Spring
Winter
1.011
Fall
0.997
All
PM10 1.020
1.014 1.000
Summer 1.650
RR
1.600 1.500 1.400 1.300 1.200 1.100 1.000 0.900 0.800
Cephalalgia 35(12)
Spring
0.998
Winter
Fall
1.000
All
NO2 1.321
1.310 1.140
1.118
1.085
1.119
1.111
0.970 0.800 Spring 2.300
Winter
Fall
Summer
All
SO2
1.800 1.620 RR
RR
1088
1.357
1.300
1.246
1.249 0.883
0.800 0.300 Spring
Winter
Fall
Summer
All
Figure 3. The effect of short-term increase in pollutant concentrations on emergency department (ED) visits for headache, by season. Relative risk (RR) and 95% confidence interval for ED visits per 10 units increase in the daily pollutants concentrations. Results of the separated Poisson regression models, for study period 2002– 2012 (N ¼ 9354 ED visits), adjusted for temperature and relative humidity in all and divided by season. NO2 ¼ nitrogen dioxide; SO2 ¼ sulfur dioxide; PM10 ¼ particles with median aerodynamic diameter of 10 mm or less.
than 40); RR ¼ 1.132 (95% CI 1.014; 1.265, p ¼ 0.028), RR ¼ 1.075 (95% CI 0.985; 1.174, p ¼ 0.106) and RR ¼ 1.003 (95% CI 0.943; 1.066, p ¼ 0.935), respectively. The effect of NO2 also increased with age: RR ¼ 1.141 (95% CI 1.049; 1.241, p ¼ 0.002) for the group age 40–60 compared to the younger patients; RR ¼ 1.057 (95% CI 0.989; 1.131, p ¼ 0.105).
Discussion In this analysis of more than 22,000 visits with headache to the ED, we have assessed the short-term effects of meteorological and air pollution factors. We have found that an increase in temperature and NO2 was associated with increased risk of headache ED visits. This effect of the ambient temperature was particularly evident during colder seasons (winter and fall). The effect of NO2 and dust storm increased with age.
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Table 3. Relative risk of headache emergency department (ED) visits associated with increase in pollutant concentrations by age, gender.
Category Gender Male Female Age groups Age 60
Dust storm
PM10 (mg/m3)
NO2 (ppb)
SO2 (ppb)
RR
95% CI
RR
95% CI
RR
95% CI
RR
95% CI
0.980 1.046
0.878 0.962
1.095 1.138
1.002 1.000
0.998 0.997
1.005 1.003
1.100 1.121
1.020 1.058
1.186 1.188
1.290 1.108
0.804 0.770
2.068 1.595
1.003 1.075 1.132
0.943 0.985 1.014
1.066 1.174 1.265
1.000 1.001 1.002
0.997 0.997 0.996
1.003 1.005 1.007
1.057 1.141 1.063
0.989 1.049 0.975
1.131 1.241 1.160
1.050 1.577 1.403
0.687 0.925 0.723
1.606 2.690 2.720
Relative risk (RR) and 95% confidence interval (CI) for ED visits per 10 units increase in the daily pollutants concentrations. Results of the separated Poisson regression models for study period 2002–2012 (N ¼ 9354 ED visits), adjusted for temperature and relative humidity in all and divided by season. NO2 ¼ nitrogen dioxide; SO2 ¼ sulfur dioxide; PM10 ¼ particles with median aerodynamic diameter of 10 mm or less; ppb: parts per billion. Boldface indicates positive statistical significant results (p-value
