Emicrania ed inquinamento

1. American Journal of Epidemiology Vol. 170, No. 8
ª The Author 2009. Published by Oxford University Press on behalf of the Johns Hopkins Bloomberg School of Public Health. DOI: 10.1093/aje/kwp217
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distribution, and reproduction in any medium, provided the original work is properly cited. September 9, 2009
Original Contribution
Air Pollution and Hospitalization for Headache in Chile
Robert E. Dales, Sabit Cakmak, and Claudia Blanco Vidal
Initially submitted February 11, 2009; accepted for publication June 25, 2009.
The authors performed a time-series analysis to test the association between air pollution and daily numbers of
hospitalizations for headache in 7 Chilean urban centers during the period 2001–2005. Results were adjusted for
day of the week and humidex. Three categories of headache—migraine, headache with cause specified, and
headache not otherwise specified—were all associated with air pollution. Relative risks for migraine associated
with interquartile-range increases in specific air pollutants were as follows: 1.11 (95% confidence interval (CI): 1.06,
1.17) for a 1.15-ppm increase in carbon monoxide; 1.11 (95% CI: 1.06, 1.17) for a 28.97-lg/m3 increase in nitrogen
dioxide; 1.10 (95% CI: 1.04, 1.17) for a 6.20-ppb increase in sulfur dioxide; 1.17 (95% CI: 1.08, 1.26) for a 69.51-
ppb increase in ozone; 1.11 (95% CI: 1.00, 1.19) for a 21.51-lg/m3 increase in particulate matter less than 2.5 lm in
aerodynamic diameter (PM2.5); and 1.10 (95% CI: 1.04, 1.15) for a 37.79-lg/m3 increase in particulate matter less
than 10 lm in aerodynamic diameter (PM10). There was no significant effect modification by age, sex, or season.
The authors conclude that air pollution appears to increase the risk of headache in Santiago Province. If the relation
is causal, the morbidity associated with headache should be considered when estimating the burden of illness and
costs associated with poor air quality.
air pollution; environment; headache
Abbreviations: ICD-10, International Classification of Diseases, Tenth Revision; PM2.5, particulate matter less than 2.5 lm in
aerodynamic diameter; PM10, particulate matter less than 10 lm in aerodynamic diameter.
Acute and chronic exposure to urban air pollution in tion were significantly worse (P < 0.05) when the women
North America and Europe has been associated with in- were exposed to ozone at 60–80 ppb as compared with <2
creased respiratory symptoms, reduced lung function, and ppb (10). Between 1992 and 2000, the daily number of
hospitalization and death from cardiac and respiratory headache-related visits to an Ottawa, Canada, hospital
diseases (1–5). emergency department increased by 4.9% (95% confidence
Headache is an important cause of morbidity in modern interval: 1.2, 8.8) with each 3.9-ppb increase in sulfur di-
society. There are many self-reported triggers for migraines, oxide level, lagged by 2 days (11). The same author also
including weather, fatigue, stress, food, menstruation, and reported an increase in headache-related visits in Montreal,
infections (6, 7). There have been few studies of the effect of Canada, associated with increases in nitrogen dioxide and
air pollution on headache. A daily diary study of 32 head- carbon monoxide levels (12).
ache sufferers in Turin, Italy, revealed that the severity and We studied the association between gaseous and particu-
frequency of headache was related to numbers of days with late air pollution and hospitalization for headache in San-
increased carbon monoxide and nitrogen dioxide levels (8). tiago Province, Chile. Santiago is densely populated and is
Reported headache was more common in a neighborhood situated in a valley surrounded by the Coastal and Andes
with a pulp mill than in one without one (9). Among 29 mountains (13–15). In 2001, Kavouras et al. (16) observed
women aged 19–27 years who were studied in an environ- that concentrations of particulate matter less than 10 lm in
mental chamber, headache, eye irritation, and nasal irrita- aerodynamic diameter (PM10) in several Chilean cities were
Correspondence to Dr. Sabit Cakmak, Division of Statistics, Health Canada, 50 Columbine Driveway, Ottawa, Ontario, Canada K1A 0K9 (e-mail:
sabit_cakmak@hc-sc.gc.ca).
1057 Am J Epidemiol 2009;170:1057–1066

2. 1058 Dales et al.
high by US and European standards, making it easier to each pollutant, using the optimal lags—those that maxi-
detect adverse effects of air pollution. mized the observed effect size. The interquartile range,
the middle 50% of the exposure data, provides a realistic es-
timate of day-to-day changes. It is nonparametric, so it will
MATERIALS AND METHODS not be influenced by skewed data. It excludes extreme
Air pollution data
values and outliers which are unstable and infrequently
seen. Results from each region were pooled using a ran-
Daily air pollution data from 2001–2005 for the urban dom-effects model.
centers that make up Santiago Province were obtained from
7 monitoring stations in 7 regions: Las Condes, Cerrillos, El
Bosque, La Florida, Independencia, Santiago, and Pudahuel. RESULTS
The Las Condes, Santiago, and Pudahuel stations measured
the pollutants ozone, nitrogen dioxide, sulfur dioxide, carbon Regional population sizes varied more than 3-fold, from
monoxide, PM10, and particulate matter less than 2.5 lm in 421,000 in Independencia to 1,335,000 in La Florida
aerodynamic diameter (PM2.5). Nitrogen dioxide was not (Table 1). The numbers of hospital admissions for headache
measured in Independencia, La Florida, or El Bosque. varied 2- to 4-fold between Santiago and Independencia. In
PM2.5 was not measured in Independencia. the total population of 5.37 million people, there was an
average of 2.5 hospital admissions daily for headache, half
of which had no specified cause and one-third of which were
Headache hospitalization data
for migraine. Twenty-four-hour mean concentrations of air
Headache was coded using the International Classifica- pollutants varied by approximately 50%–100% between re-
tion of Diseases, Tenth Revision (ICD-10). Daily numbers gions. El Bosque had the greatest concentrations of PM10
of hospitalizations for migraine (ICD-10 code G43), other and sulfur dioxide and the second-greatest concentration of
specified headache (tension, cluster, vascular, posttraumatic, sulfur dioxide. Las Condes had the greatest concentration of
drug-related, or other specified cause; ICD-10 code G44), ozone.
and headache not otherwise specified (ICD-10 code R51) The greatest and smallest regional pairwise correlation
were obtained from the Instituto Nacional de Estadisticas, coefficients for each 2-pollutant combination are presented
the official source of statistical data in Chile from 2001 in Table 2. Those greater than or equal to 0.7 are identified
through 2005. Atypical facial pain and trigeminal neuralgia with a footnote. The greatest positive correlations were be-
were not included. tween carbon monoxide and nitrogen dioxide and PM2.5,
which is consistent with a common source, mobile combus-
tion. Sulfur had somewhat lower positive correlations with
Statistical methods
the other pollutants, whereas ozone tended to have small and
We assumed a Poisson distribution and used time-series often negative correlations with other pollutants.
analyses. A linear association between ambient air pollution
and headache on the logarithmic scale was assumed (17). Associations between headache and single pollutants
Natural splines were created with 1 knot for each of 15, 30,
60, 90, 120, 180, and 365 days of observation. We selected The majority of relative risks for the relation between head-
a model with the number of knots that minimized Akaike’s ache and air pollution were greater than 1 for each of the 7
Information Criterion, a measure of model prediction. We areas and each of the 3 headache classifications (Table 3).
then maximized the evidence that the model residuals did Of all of the relative risks calculated for each pollutant
not display any type of structure, including serial correlation by region and by headache type, ozone had greater relative
using Bartlett’s test (18). We also plotted model residuals risks than the other pollutants for 14 of the 21 comparisons.
against time, searching for visual signs of a pattern or cor- Of the 3 headache types, relative risks were greater for
relation. Having selected the optimal model for time, we migraine for approximately 50% of the comparisons. The
assessed the 24-hour mean values for temperature, humidity, 95% confidence interval excluded 1 for 15 of the 21 com-
barometric pressure, and humidex (a measure of the com- parisons with ozone, 7 of the 12 comparisons with nitrogen
bined effect of temperature and humidity; Environment dioxide, and 6 of the 12 comparisons with PM2.5. For other
Canada, unpublished data, 2002 (http://www.msc-smc.ec. pollutants, fewer than 50% of the comparisons were signif-
gc.ca/cd/brochures/humidity_e.cfm)) to determine the best icant. The number of times the 95% confidence interval
weather predictors of headache. We accounted for potential excluded 1 was 22 for migraine, 9 for nonspecified head-
nonlinear associations with headache by using natural spline ache, and 7 for specified headache. Las Condes and Santiago
functions with 4 knots. The model that minimized Akaike’s had the greatest numbers of significant relative risks. There
Information Criterion used humidex, both on the day of the were significant associations between migraine and ozone in
hospital admission for headache and on the day prior. all regions.
Lag times of 0–5 days were examined for the air pollut- When the regions were pooled, the relative risk estimates
ants. We also used unconstrained distributed lags as de- were greater than 1 for all pollutant-headache type combi-
scribed by Schwartz (19). nations. Using models with a single lag structure, the 95%
In this paper, we present the increase in relative risk of confidence interval excluded 1, except for the associations
headache for an interquartile-range increase in the level of between PM2.5 and migraine and headache of specified
Am J Epidemiol 2009;170:1057–1066

3. Air Pollution and Hospitalization for Headache 1059
Table 2. Minimum and Maximum Pearson Pairwise Correlations
Change
12.23
18.93
34.20
23.35
21.51
1-IQR
Between Air Pollutants for 7 Urban Centers, Santiago Province,
PM2.5, mg/m3
Table 1. Populations, Daily Numbers of Hospitalizations for Headache, and 24-Hour Ambient Air Pollution Concentrations in 7 Urban Centers, Santiago Province, Chile, 2001–2005
Chile, 2001–2005
Abbreviations: IQR, interquartile range; PM2.5, particulate matter less than 2.5 lm in aerodynamic diameter; PM10, particulate matter less than 10 lm in aerodynamic diameter.
Carbon Sulfur Nitrogen
b
Mean
Pollutant Ozone PM10
26.05
34.22
62.65
33.62
32.48
Monoxide Dioxide Dioxide
Change Ozone
22.11 Minimum À0.514**
41.92
41.06
36.43
34.07
38.84
42.75
37.79
1-IQR
PM10, mg/m3
Maximum À0.176
Sulfur dioxide
b
Mean
52.49
73.16
77.79
76.77
67.55
69.94
73.58
72.24
Minimum 0.418** À0.088*
Maximum 0.821 0.129
Nitrogen dioxide
Change
30.21
32.43
32.70
22.09
28.97
1-IQR
0.788a,** À0.339** 0.416**
Dioxide, ppb
Daily Air Pollution Concentration
Minimum
Nitrogen
b
Maximum 0.844a À0.085 0.797
PM10
Mean
52.77
44.43
44.72
40.13
44.74
Minimum 0.512** À0.003** 0.387** 0.614**
Maximum 0.835 0.169 0.839 0.787
Change
1-IQR
3.74
8.62
7.25
5.47
6.33
6.27
4.91
6.20
PM2.5
Dioxide, ppb
Minimum 0.729a,** À0.310** 0.390** 0.716a,** 0.712a,**
Sulfur
Maximum 0.915a À0.069 0.825 0.823a 0.917a
b
Mean
5.97
8.97
9.06
7.21
9.32
11.17
11.21
10.74
Abbreviations: PM2.5, particulate matter less than 2.5 lm in aerody-
namic diameter; PM10, particulate matter less than 10 lm in aerodynamic
Change
diameter.
56.84
52.92
78.40
72.52
73.99
50.96
69.51
121.50
1-IQR
* P < 0.05; **P < 0.005.
a
Ozone,
Pearson pairwise correlation coefficient of 0.7 or greater.
ppb
b
88.52
81.28
83.52
96.20
82.73
93.26
124.10
101.41
Mean
cause and the association between nitrogen dioxide and
headache of specified cause (Table 4). The largest risk esti-
Change
Monoxide, ppm
mate was 1.17 for the relation between ozone and migraine
1-IQR
0.57
1.13
1.22
1.28
1.27
1.40
1.04
1.15
headache, and the second-largest was 1.13 for the relation
Carbon
between nitrogen dioxide and headache of specified cause.
Effect sizes seen with a distributed lag structure pointed in
b
Mean
0.81
0.94
1.24
1.27
1.06
1.21
1.09
1.11
the same direction but tended to be greater than with the
single lag structure. With distributed lags, the only 95%
Specified
a
confidence interval not excluding 1 was that for the associ-
Cause
0.101
0.059
0.077
0.113
0.125
0.033
0.053
0.561
Daily No. of Hospitalizations,
ation between migraine and PM2.5. There was no consistent
by Headache Type
effect modification of the headache-pollution associations
by age, sex, or season (Table 5). Compared with younger
Population weighted average pollutant concentration.
Migraine
a
0.127
0.095
0.095
0.138
0.150
0.053
0.086
0.744
persons, those over age 64 years had nonsignificantly larger
Total number summed over all 7 urban centers.
relative risks for headaches other than migraine.
Otherwise
Specified
Associations for headache in 2-pollutant models
a
0.114
0.057
0.104
0.102
0.135
0.046
0.061
1.168
Not
For migraine, the relative risk point estimates for nitrogen
dioxide remained stable and statistically significant after
adjustment for each of the other pollutants (Figure 1). When
Population
a
(3105)
5.01
8.92
9.15
4.21
4.98
8.08
13.35
53.70
other pollutants were adjusted for nitrogen dioxide, their
point estimates decreased and statistical significance was
lost. The point estimate for PM10 remained stable despite
adjustment for pollutants other than nitrogen dioxide. Car-
Combined results
bon monoxide, sulfur dioxide, and ozone lost significance
Independencia
when adjusted for nitrogen dioxide or PM2.5. For both head-
Center
Urban
Las Condes
El Bosque
La Florida
Pudahuel
ache–not otherwise specified and headache–specified cause,
Santiago
Cerrillos
the results from 2-pollutant models were similar. The rela-
tive risk point estimate for carbon monoxide remained sig-
a
b
nificant when adjusted for other gases but lost significance
Am J Epidemiol 2009;170:1057–1066