Exposure to birch pollen and the risk of allergic and asthmatic
manifestations
A short running title: Birch pollen exposure and allergic
manifestations
Keywords: Allergy, asthma, personal exposure, pollen,
regional exposure
Birches are the most dominant pollen type in Northern Europe and have a
major role in the development of pollen-related allergic and/or
asthmatic symptoms in Northern Europe.1-3 Little is
known about potential effects of daily personal pollen exposure on daily
allergic and asthmatic manifestations.4 This is the
first study that utilizes personal monitoring in exposure assessment and
investigates exposure to birch pollen in relation to pattern of allergic
and/or asthma symptoms (including timing, sequence, duration, and
intensity).
We assessed potential relations between short-term (daily) exposure to
birch pollen and manifestations of allergies and asthma among adults who
already had allergic rhinitis and/or asthma. We hypothesized that: 1)
Exposure to the peak of pollen concentration is followed by an increase
in allergic and/or asthmatic manifestations, 2) A certain biologically
plausible sequence can be detected in the occurrence of allergic and/or
asthmatic manifestations, 3) A typical duration of allergic and/or
asthmatic manifestations can be detected and this depends on the order
in which these symptoms occur, and 4) Exposure to the peak of pollen
concentration impairs the allergy and asthma control among subjects who
have these diseases.
We conducted a panel study among the Espoo cohort members between April
18 and May 24, 2014, in the Helsinki Metropolitan Area during birch
pollen season.5-6 A total of 19 participants who had
allergic rhinitis (N=19) and/or asthma (N=16) monitored their daily
personal pollen exposure and registered their daily symptoms. Daily
allergy and asthma control, inquired in daily diary, were categorized as
follows: 1 = Good, 2 = Somewhat under control, 3 = Poorly under control,
4 = Not at all under control. (see extended Methods, online
supplementary material).
The mean daily regional pollen
concentrations varied between 18 and 27435 and the mean daily personal
pollen exposure varied between 20 and 16773 pollen grains per cubic
meter of air during the follow-up period.
Both asthma and allergy control started to decline after people were
exposed to pollen peak. Allergy control deteriorated on average 0.268
(95% CI 0.087-0.449; P = .004) and 0.038 (-0.062-0.138; P = .46) units
when exposed to abundant levels of pollen, and further 0.358
(0.184-0.532; <.001) and 0.096 (-0.012-0.204; P = .08) units
when exposed to extremely abundant levels of pollen compared to controls
in regional and personal monitoring. (Table 1). Similar trends, although
statistically nonsignificant, were detected in asthma control.
Allergy symptom score reached its peak (highest value) simultaneously
with the highest pollen peak and was found to follow the trend of pollen
exposure more closely. In contrast, asthma symptom score peak occurred
with a short lag after the highest pollen concentration and remained at
a reduced level during the entire follow-up period. Furthermore, it
peaked later after a few additional minor pollen peaks (Figure 1). Most
of the participants reported that their symptoms peaked after the
regional and the personal pollen peak (Exact binomial test: P values
varied between .059 and < .001) (Table S1). The nasal system
reached its peak first after the peak day of pollen concentration (range
in average symptoms peak day 13.1–14.8), followed by throat
(14.2–15.9), skin (14.5–15.1), and eye systems (15.4–16.2). Lower
respiratory symptoms needed the longest induction period (17.8–18.3)
before their peak took place (Table S2).
Worsening of both allergy and asthma symptoms started concurrently with
the first peak of birch pollen. Both allergy and asthma control were
poorest on the day with abundant and extremely abundant pollen
concentrations, but then followed different patterns thereafter. We
showed for the first time that there is a biologically plausible
sequential order in the occurrence of symptoms after the high pollen
exposure.