The age of the participants varied between 19 to 56 yr. The group consisted of 3 males and 9 females. The first day of the study period appeared to be a day with very high grass pollen counts (Figure 2) and three participants decided to leave the study since they could not meet the criterium not to use medication; 2 males and 7 females completed the study. The GPS IgE levels in the serum of these patients varied between 1.4 to 93 kU/L with a geometric mean of 9.6 (Table 1).
Collection of pollen
Since the participants were asked to collect the pollen on their way to school or work during the time they were outside, the collection time varied for the different samples in a range from 15-40 minutes. The participants were asked to collect pollen on 14 different days spread over the 4 weeks (May 28th and June 20th, 2018). Most participants (6) collected pollen for 14 days or more, while some (3) participants could only collect pollen during 9, 11 or 13 days. Most samples were collected on a bicycle (Table2). The range of pollen collected by the participants varied hugely; the lowest number of pollen grains was 2 and the highest number 4017 pollen grains (Table 2).
Participants S03 and S16 had some minor incidents handling 2 and 3 slides, respectively, and participants S04 had an incident with the sampling box which may have affected the integrity of the sample slides. All these slides were microscopically analysed, and although no discrepancies with the other slides was observed, there may be a chance that the number of pollen grains on the slides was affected by the incidents (see also later).
In all Pollensniffer samples, grass pollen was by far the most numerous pollen type. Other allergenic pollen types, like tree pollen, birch, alder, ash or oak, never exceeded 1% of the number of grass pollen. Weed pollen, such as sorrel, plantain or mugwort, never exceeded 5 % of the number of grass pollen in the samples.
Correlation between symptoms and pollen collected by Pollensniffer
In a first analysis, we found significant correlation between either one of the clinical symptom scores and the pollen count in the Pollensniffer samples for only three participants. We noticed that these 3 participants were the ones with the higher GPS IgE levels and the higher symptom scores. Based on this observation, the participants were split into 2 groups, according to their GPS IgE levels. Since the IgE levels were not normally distributed we took the geometric mean of the GPS IgE levels to divide the participants into group 1 (GPS IgE levels > 9.6 kU/L) and group 2 (£ 9.6 kU/L) (Table 1). The different symptoms were correlated with the pollen collected by the participants. Three of the four participants (S01, S06 and S15) from group 1 (high GPS IgE levels) showed a significant correlation (Figure 3 and Table 3) for one (S01 and S15) or two (S06) types of symptoms. These participants had no other sensitizations or other sensitizations with low specific IgE levels (Table 1), and their range of symptom scores was large (from 0 to > 5). The scatter plot of results from participant S07 (Figure 3, Table 3) showed a non-significant moderate correlation for lung symptoms; some data points correlated by increasing symptoms with increasing number of pollen collected, but other data points show a 0-score for the symptoms when relative high numbers of pollen were collected (Figure 3).
The five participants in group 2 (low GPS IgE levels) showed moderate, none or even negative correlation and between the symptoms and the pollen collected (Figure 3 and Table 3). Participant S04 showed a moderate positive correlation. Participants S16 and S03 both had incidents with 2 or 3 slides but leaving out the data points belonging to those slides did not significantly alter the outcome of the analysis. These participants had very low IgE levels to grass pollen and their symptom scores were low (< 2). Participant S14 submitted the symptom scores during the evening and may have scored the symptoms over the whole day and not directly after exposure during the sampling. Participant S18 showed no or negative correlations with all types of symptoms. This participant had relatively high IgE level towards house dust mite and trees. Furthermore, this participant had received grass pollen immunotherapy more than 10 years ago. These conditions might have affected the relation between grass pollen and symptoms.
These results show correlations between the severity of symptoms and the personal grass pollen exposure especially in patients with high GPS IgE levels, high symptom scores and no other relevant sensitisations.
Correlation between clinical symptoms and daily pollen concentrations at rooftop level
We next investigated the relationship between these symptom scores and the pollen counts derived from the nearby local pollen monitoring station collected at rooftop level at the LUMC. Significant positive correlations between symptom scores and daily pollen counts were found in the group with the high GPS IgE levels (group 1, Table 4). For participants S01 and S15 the same type of symptoms, that correlated significantly with the Pollensniffer pollen counts, showed a significant correlation with the daily rooftop pollen concentrations. Participant S06, that showed significant correlations for lung and nose symptoms with the pollen collected by the Pollensniffer, did not show a significant correlation for any type of symptoms with the daily pollen counts at rooftop level. In contrast, symptoms of participant S07, which showed only non-significant moderate correlation with the Pollensniffer pollen counts, correlated for lung symptoms significantly with the daily rooftop pollen concentrations (Table 4). Two of the participants (S14 and S18) with low IgE levels even showed a significantly negative correlation with the daily pollen concentrations at rooftop level. These findings illustrate that also when using pollen counts from the rooftop sampler, correlation with symptom scores were especially found in those patients with high symptom scores, high GPS IgE levels and no other relevant sensitizations.