ASTHMA AND WEATHER: RELATIONSHIP OF WEATHER TO ASTHMA ATTACKS IN WELLINGTON
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Weather and Climate (1989) 9: 15-22 15
ASTHMA AND WEATHER: RELATIONSHIP OF WEATHER TO
ASTHMA ATTACKS IN WELLINGTON
Paul Bruce
New Zealand Meteorological Service
P.O. Box 722, Wellington, New Zealand
ABSTRACT
A number of well marked seasonal peaks of asthma attacks are found in a one year
study of 30 patients (Beasley et al., 1988) in Wellington. The seasonal impact of various
meteorological indices and their causal relationships with asthma are investigated.
It is found that damp, light wind conditions in winter are significantly related to the
frequency of asthma attacks. This is consistent with such attacks being caused by damp
air spora and other allergens present i n confined environments such as houses.
Overland trajectories are also significantly correlated with asthma attacks. In autumn
this may be attributed to damp air spora produced in rural areas to the north and
northeast, and in spring to airborne pollens. No clear relationships were found linking
cold changes to asthma.
INTRODUCTION
Asthma is a condition which causes consid- explain asthma (Tromp, 1980). The allergen
erable concern in New Zealand. For example, theory attributes complaints to allergic reac-
an Auckland study (Mitchell, 1984) indicated tions; the 'cold chill' theory is said to be due to
that hospital admission rates for asthma had a deficient hypothalamic thermoregulatory
increased greatly since the mid 1960's, and a mechanism (deficiency in rewarming capabil-
recent national (NZ) asthma mortality study ity); the infectious theory assumes early bron-
(Sears et al., 1985) showed a mortality rate chial i n f e c t i o n s o f a c h i l d ; t h e
three times that of the United Kingdom. endocringological theory attributes the com-
In this study, possible relationships are in- plaints to endocrinological disturbances (part-
vestigated between attacks suffered by asth- ly true in children during puberty and women
ma patients undergoing treatment a t t h e around the age of 50); and the psycho-somatic
Wellington Clinical School f o r the 11 month theory explains a l l complaints i n terms o f
period 12/1/84 to 17/12/84, and the weather psycho-somatic disturbances (once a subject
over that period. becomes an asthmatic, psychological factors
The American Thoracic Society has defined may become important due to continous respi-
asthma as " a 'disease' characterised b y an ratory problems). Clearly some o f these
increased responsiveness of the trachea and causes will be related to the weather.
bronchi to various stimuli, and manifested by In this paper the weather patterns affecting
a widespread narrowing of the airways, that Wellington are briefly described. Some of the
changes in severity either spontaneously or as factors likely to cause asthma attacks, and
a result o f therapy". Asthma can also be weather conditions under which such factors
described as an inflammatory disorder. Nar- are likely to occur, are identified. The asthma
rowing of the airways includes bronchospasm, and weather data a r e then examined and
mucous production and mucosal oedema. conclusions drawn about likely relationships
Various theories have been put forward to in Wellington.16 Asthma and Weather
NEW ZEALAND A N D WELLINGTON'S WEATHER moist north or northeast airstreams to flow
AND CLIMATE
over the country, followed b y a southerly
New Zealand lies in the mid-latitude zone of outbreak.
westerly winds, i n the path o f an irregular Wellington's proximity to Cook Strait (see
succession o f anticyclones which migrate Fig. 1) leads to a high frequency of strong
eastwards every week or so ( N I . Met. Ser- winds channelled b y t h e topography t o
vice, 1986). The centres of these anticyclones north/south direction. Westerly airstreams
generally track across the North Island with are deviated to the northwest, and easterlies
more northerly paths being followed in spring are normally deflected to the south. I n very
and summer, and southerly paths in autumn unstable situations, these airstreams are less
and winter. Anticylones are areas of descend- affected by orography.
ing air and settled weather, with little or no For the year of the study, 1984, Wellington
rain, which m a y bring clear skies, o r l o w had a mean temperature of 13.1 ' C (0.6 de-
cloud and fog. grees warmer than the average from 1928 to
Between the anticyclones are troughs of low 1980), 1054 m m of rain (20% less than the
pressure. Within these troughs there are often average) and gales on 19 days (15% fewer
cold fronts, orientated north-west t o south- days than average).
east, which produce one o f the commonest
type of weather sequence over the country: as FACTORS ASSOCIATED WITH ASTHMA ATTACKS
the front approaches from the west, north- Cold Chill Effect
westerly winds become stronger and cloud
increases, followed by a period o f rain f o r Tromp (1980) found a highly significant sta-
several hours as the front passes over, and tistical relationship between asthma frequen-
then a change to cold showery southerlies. cy and atmospheric cooling. Another more
The frequency of the above systems shows recent study i n Japan (Suzuki e t al., 1988),
little variation with season except for an in- showed that low temperature and decrease in
crease in anticyclonic activity in autumn, al- temperature was singificantly related with
lied t o a corresponding decrease i n t h e the asthmatic symptom. However it was notes
frequency of troughs. Another feature of au- that further studies were necessary to know
tumn is the occasional appearance of decay- whether 'the state o f the atmosphere and
ing tropical cyclones in the area to the north contents of the air collaborate on the airway
to evoke the asthmatic condition'.
of the North Island, which can cause very
This present study investigates asthma data
for evidence o f this cooling effect. A s the
exact time o f the asthma attack was not
available, a relationship between daily asth-
ma frequencies and a change from the warm-
er northwesterley airstreams t o t h e cold
southerly wind was examined.
The data are also examined f o r seasonal
variations, a s pollen releases occurring i n
spring with westerley winds may have a con-
founding influence.
Allergen theory
The allergic reactions of asthmatics have
been r e l a t e d t o seasonal p o l l e n peaks
(Tonkelaar, 1986), to seasonal pattern of air-
borne damp air fungal spores (Hasnain et al.,
1985; Packe e t al., 1985), t o the dust-mite,
animal proteins and fungal spores that occur
in confined environments, in addition to tobac-
co smoke and other aero-irritants (Mathison et
al., 1982).
Fig I : Location of Wellington and relative frequency of
Westerly, Southerly, Northerly, and Light and Variable Damp air fungal spores (open environment)
sector winds. Studies show that pollens are only weaklyAsthma and Weather 17
represented in autumn, but other allergy-pro- live mite populations diminishing rapidly for
ducing micro-organisms, especially fungal humidities below 4 5%
spores from the basidiospore group (damp air Fungal spores, the house mite, and other
spore component), a r e especially favoured contaminants known to cause asthma, such as
(Hasnain et al., 1985; Pennycook, 1980). formaldehyde in treated plywood or particle
Factors contributing t o higher damp a i r board and glues (Matthews, 1985; Yodaiken,
spore concentrations will be: high night-time 1981; Robertson et al., 1986), have been identi-
humidity (more likely in Autumn with length- fied in the indoor environment. Their impact
ening nights and a seasonal lack o f wind); would b e exacerbated i n badly ventilated,
rising air motion at ground level; and winds damp buildings, a set of conditions most likely
blowing overland towards the observer. Ris- to occur with cold, wet periods or low winds
ing air motions occur with day-time convec- and shorter sunlight hours, in April through to
tion on sunny days, and are especially strong July (late autumn and winter). New Zealand
in airstreams preceding active fronts or dur- houses may be especially susceptible to the
ing thunderstorms when the atmosphere i s influence of prolonged damp periods, due to
'unstable' (defined in Data and Methods). the predominance of wood, which will absorb
Acccording to Hasnain et al., (1985) urban moisture when badly protected.
areas with restricted vegetation provide less In addition, there may be a tendency in the
opportunity for fungal growth than forest or early winter period to keep windows shut to
farmlands. Hasnain also documented a close conserve heat in inclement weather. A behav-
association between the basidiospore and hos- ioural response to cold changes of restricting
pital admissions for acute asthma. In the case air movement and closing windows (following
of Wellington, the north to east sector has the a retreat indoors to a confined environment),
largest overland and rural trajectory and thus will result in a higher humidity air mass and
airstreams from those directions would be higher concentrations of pollutants and aller-
expected to contain higher concentrations of gens. The relative humidity will be higher in
spores. unheated rooms, typically bedrooms, w i t h
condensation on cooler surfaces of humid air
If allergens are present when the wind is from warmer parts of the house. Localised
blowing from the north to east sector, and i f warmth in beds (from body heat), in combina-
the asthma is related to the contents of the
tion with this dampness, may then produce the
airstream, then a wind change t o a shorter ideal environment for the house mite.
overland trajectory (westerlies or southerlies) To ensure that there i s no compounding
should decrease spore concentrations and thus factor. of damp air spores orginating from the
the number of asthma attacks. To avoid the
external environment, t h e contribution o f
possible confounding influence o f the 'cold moist long overland trajectory northerly air-
chill' effect associated with the change to the streams was also investigated. In spring, high
south, only the change t o the westerly flow wind levels, increasing insolation and warm-
was investigated. ing temperatures will result in a decrease in
House mite and damp a i r spores in confined dampness i n the house, and asthma should
environments then decrease.
The Wellington study on aero-allergeds in Cold changes that arrive after midnight
the homes of asthmatics (Sheridan et al., 1985) when potential sufferers are probably in bed
indicated a range of fungi known to be signifi- (and most likely to be subject to allergens
cant in asthma. These showed seasonal varia- such as produced b y the house mite), m a y
tions, with the number of colonies of two of result in the behavioural response of shutting
the m o s t frequent, basidiomycetes a n d any windows that remain open. This would
cladosporium, showing a decrease i n t h e lead to higher concentrations o f allergenic
months July, August and September. gases or spores with a corresponding increase
The mite of the genus 'dermatophagoides', in the r i t e of asthma attacks.
one of the most significant causes of asthma, Pollen, dry air spora
occurs in house dust and is temperature and Pollen releases occur in spring and continue
humidity dependent (Mathison e t al., 1982; into summer, when other dry a i r spora re-
Korsgarrd, 1982). Optimal growth occurs at 25 leases become important. T h e triggering
degrees C and 80% relative humidity, with mechanism is some initial dampness, rising18 Asthma and Weather
temperatures, and the absence of rain during Asthma was defined with reference t o a
the critical period of release. Each plant has peak flow meter, and confirmed b y other
its own favoured period of release of pollen. measurements when patients reported to the
Pollen grains on release are entrained b y clinic (Beasley et al., 1988).
wind gusts and by small turbulent wind ed- The daily weather elements used were max-
dies. Peaks in concentration may occur during imum and mean temperatures, wind run, and
the day or at night time when a temperature significant rain at Kelburn (Wellington). Other
inversion occurs in the atmosphere trapping indicators such as wind direction, frontal pas-
spores i n a relatively shallow layer o f the sage, change of airstream, and atmospheric
atmosphere (Tonkelaar, 1986). I f spore re- stablility indicators were derived from inves-
leases are occurring upstream, large local tigation of synoptic charts. Results were found
concentrations may then occur. Rain clears to be best represented for the four seasons,
the atmosphere of contaminants and suppress- defining autumn a s February, March and
es pollen production, so some allergic symp- April; winter as May, June and July; etc.
toms should b e a l l e v i a t e d d u r i n g a n d Airstream winds over Wellington are cho-
immediately after rain. However, note that sen by sectors to highlight over-land and on-
considerable amounts of damp air spores may shore components:
then be produced, resulting in problems for a a) Northerly - the overland sector repre-
different set of subjects. senting north, northeast, east winds.
Wellington suburban gardens are f u l l o f b) Northwest - the short overland sector
flowering species, and the unoccupied hills to representing northwest and westerly winds.
the north, west and east, are covered in gorse, c) Southerly - the oversea (onshore) sector
pine trees and native bush. A study in Welling- representing southwest, south, and southeast
ton (Licitis, 1952) indicated that marked pol- winds, which are generally associated with
len peaks occured i n spring, i n the period lower temperatures.
August through to October. If this relationship d) Light and variable - conditions which
holds, we would expect significantly higher might indicate a short overland trajectory,
level o f pollen and high asthma levels i n local allergen sources, or factors relating to a
spring during fine weather with winds arriv- confined environment.
ing from the west through north to east sector. Unstable conditions in the atmosphere indi-
Southerlies, representing the sector which has cate upward, often turbulent motion of air,
the smallest surburban trajectory, should con- and also the tendency for airstreams to flow
tain the least amount of pollen spores given over, rather than around hills. When a trough
other ideal conditions. The predominant winds of low pressure of cyclonically curved isobars
of spring are northwesterlies and these are on the synoptic map is present, the airmass is
normally d r y (apart from brief periods o f taken to be unstable. In cases where there is
showers), and turbulent. some uncertainty, the presence of significant
DATA AND METHODS quantities of rain (greater than 0.5 mm) is
This study uses asthma data on 30 patients noted a s indicating atmospheric dynamic
collected by the Wellington Clinical School. instability.
Patients came from a range of occupations RESULTS
and ages. All resided in the Wellington region, Over the 336 day period of the study, indi-
except for one who commuted daily from the vidual attacks persisted for an average of 3.4
Wairarapa. The group were asked to record, days but could extend up to 19 days. The mean
on forms, when asthma attacks began and daily asthma 'onset' rate totalled for the 30
finished in the period from 17th January to the patients is 0.5 attacks per day, with a maxi-
17th December 1984 (336 days). mum occurrence o f 3 onsets per day. The
The asthma data were categorised in two mean asthma occurrence is 1.6, with a maxi-
ways: mum value of 6. Major peaks in asthma occur-
a) Asthma Onsets. The numbers of patients rence (Fig. 2 ) w e r e observed i n autumn
suffering an onset of an attack on any day. (centred around late March) and i n winter
b)Asthma Occurrence. The number of pa- (end of July), with smaller ones in spring (late
tients suffering from asthma on any one day. October) and summer (early December).
This includes onsets and characterises the A three factor analysis o f variance was
persistence of asthma. used to show that variations by season, stabil-Asthma and Weather 19
3
Fig 2: Seasonal variation o f asthma (smoothed over 31
days).
Asthmaatacksp
e
d
ray.
Ons
/
Autumn Winter
0 1 oo 200 300 400
Julian day
ity and wind direction are significant at the 3
5% level (F-test). The null hypothesis, 'that
there is no difference i n asthma levels be- 2
tween environmental factors', was tested us-
ing a one tailed t-test on paired differences. GO G O 0 0 El
The analysis was also carried out on the
square root of asthma levels to 'normalise' the
data.
Cold chill effect: G
The change from west to southerly sectors •-2
occurred on 21 days with a mean decrease in Autumn W i n t e r S p r i n g S u m m e r
temperature of 2.3 degrees C. The increase in Fig. 3 : Impact o f change from westerly t o southerly
asthma by .04 onsets per day is significant at sector (cold change) on asthma levels.
only the 10% level (p < 0.07). There is a hint of
a "U" shape response, of reduced asthma on-
sets in winter and spring, and increased asth- 2-
ma onsets at other times of the year. Fig. 3
shows that the onset response t o southerly
change is very scattered, but with a tendency
to increased onset. There were ten cases of
increase, seven cases of no change, and four
cases of decrease. 03 133
Fig 4 : Impact o f change from northerly t o westerly -2 n
sector (cutt-off o f long trajectory spores) on asthma
levels.
-3 0
Autumn W i n t e r S p r i n g S u m m e r20 A s t h m a and Weather
Damp a i r f u n g a l s p o r e s ( e x t e r n a l 1.5
environment)
The change from northerly to westerly sec-
tors occurred on 20 occasions over the year
with a mean decrease of 0.9 asthma onsets (p 1.0
< 0.005). Fig. 4 shows the influence o f this
change in sector on asthma levels through the
year.
In autumn the most dominant factor associ-
ated with asthma levels is the presence o f
northerlies (mean temperature around 17 deg
C). Asthma levels in autumn for the northerly
sector airstreams and for light and variable Do
condiitons, are found to be significantly higher 2 6 1 0 1
than that for northwesterlies (p < 0.025). On Time of day NZ standard time (hrs)
the 3 autumn days with thunder and lightning Fig 6: Impact o f arrival time o f southerly changes in
events, mean asthma persistence levels were Wellington (with standard error bars) on daily asthma
onset rate.
167% above the seasonal mean, but this was
not significant due t o the l o w number o f From winter to spring, the decrease in asth-
events. No clear correlations were found with ma onsets overall i s significant (p < 0.05).
airmass instability and the passage of fronts. However, there is a more highly significant
drop for both unstable and wet conditions (p<
House mite and damp air spores in the inter- 0.005), and similarly for southerly sector wind
nal environment conditions (p < 0.005).
In winter, the most important factors influ- A higher asthma onset rate i s observed
encing the number of patients suffering asth- when southerly wind changes arrive during
ma attacks a r e found t o b e atmospheric the night hours (Fig. 6). Individual standard
instability, rain, southerlies (mean tempera- error bars show that changes over four hour
ture 8 deg C), and light o r variable wind adjacent p e r i o d s a r e n o t n e c e s s a r i l y
conditions. These relationships, shown in Fig. significant.
5, are observed to begin in Autumn. The over-
all seasonal change in asthma rate from au- Pollen, dry air spora
tumn to winter is not significant. However for In spring, the mean rate of asthma attacks
northerly conditions there i s a significant per day is significantly lower than that for the
decrese in importance in winter (p < 0.025), other seasons (Fig. 2). Asthma occurs most
clearly indicating the lower importance of the readily for northeasterlies, in this period (Au-
overland sector at this time of the year. gust, September, October) with levels signifi-
- cantly above those occurring for southerlies (p
O Stable < 0.025), a reversal of the situation found in
tO Unstabaa winter. The decrease from winter to spring in
mean asthma levels occurring with southerly
airstreams, is also statistically significant (p <
0.005).
Rain inhibits asthma in spring (p 0.025) in
contrast to winter, where rain is associated
with high asthma occurrence. The change in
relationship is highly significant (p < 0.001).
The six changes from westerly to southerly
airstreams found i n spring led t o a mean
decrease of 0.9 asthma onsets (pAsthma and Weather 2 1
November/December p e r i o d w i t h these lution, a n d , a s a result, asthma l e v e l s
airstreams. (Mathison et al., 1982). A tendency towards
higher asthma levels i n the early morning
CONCLUSIONS
hours may also be an indication of a stronger
A number of different meteorological influ- influence o f internal environments a t that
ences have been found to be associated with time.
asthma attacks through the year. These are Further research is needed to clarify the
highlighted at peak times: importance in New Zealand of these allergens
— an autumn peak associated with northerly and their relationship to environmental and
airstreams; behavioural factors. T h e correlations also
— the winter peak associated with a wet, low point to a possible relation between meteoro-
wind period; logical conditions and asthma which might be
— and the spring peak associated with dry found in specific microclimates, such as damp
weather and winds f r o m t h e overland river valleys. The data collected in this study
sector. did not include where people actually were,
The periods of asthma may be attributed to when they experienced their asthma attacks -
allergens of distinct varieties: the importance of micro-climates in asthma
Autumn — outdoor spores, damp variety pre- incidence i n New Zealand deserves further
dominating and originating from study.
inland sector; The asthma attack rates found in this analy-
Winter — i n d o o r spores, house mite and oth- sis indicate the origin o f asthma-producing
er contaminants; allergens present i n spring and summer -
Spring — l o c a l pollens; northwesterly airstreams and light wind situ-
Summer — airborne spores (mainly dry vari- ations representing pollens derived from local
ety) from inland sector. vegetation in spring, and northerlies and east-
The close correspondence of northerlies in erlies representing longer trajectory pollens
autumn with asthma indicates a seasonal re- and spores f r o m r u r a l and forested areas
lationship w i t h a n airstream t h a t has the further afield in summer.
larges overland bias. Studies such as that done The cold chill factor is not clearly shown to
by Hasnain et al., (1985), suggest damp a i r be present. This may be due to possible con-
spores as the allergen responsible f o r the founding factors resulting from a behavioural
asthma attacks. response to colder conditions, or to the gener-
The present study suggests that a major ally small temperature drops experienced in
asthma peak also occurs with wet, low-wind Wellington's maritime climate.
or cold conditions in winter, which is likely to ACKNOWLEDGEMENTS
be a t least partly related t o a behavioural
response of retreating indoors to closed envi- I thank the staff of the Wellington Clinical
ronment. This is supported by the finding that School for advise and the use of data, and also
during winter, the northerly overland winds Reid Basher, Steve Goulter, John Revfeim and
have the lowest correspondence with asthma. others for discussions and helpful reviews.
A marked change in environmental conditions
associated with asthma attacks then occurs REFERENCES
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