Bernard Clot

Trends in airborne pollen: An overview of 21 years of data in Neuchâtel (Switzerland)

Airborne pollen analysis has been carried outin Neuchâtel (Switzerland) since 1979. Inthe context of increasing prevalence of pollenallergies and global climate warming, thisstudy attempts to confirm whether airbornepollen may be responsible for the former orindicative of the latter, and presents somegeneral features of pollen flight in westernSwitzerland.The most common pollen types are Taxus/Cupressaceae, Quercus, Poaceae, Pinus,Betula, Urticaceae and Fraxinus. Duringthe 21 years studied, there was no major changein the abundance of pollen. Among thetwenty-five taxa studied only five presented asignificant trend: an increase of pollenquantities was observed for Alnus,Ambrosia, Artemisia and Taxus/Cupressaceae and a decrease for Ulmus. The plant species flowering in winterand in spring were influenced by the mildwinters of the 1990s: 71% of the dates of theonset or the end of the pollen seasons nowadaysoccur significantly earlier in the year. Theobserved advance reaches 0.84 days/year. Treesappear to react stronger to the climate changethan grass and weeds. No pollen type present aprolonged season, so the trend appears to betowards a shift in the timing of pollenpresence in the air.These observations show that the main cause ofthe spectacular increase of pollinosisprevalence in industrialised countries isprobably not to be found in the weak tendencytowards a rise of pollen abundance, except forsome particular pollen types which can broadenthe spectra and/or intensify the abundance ofmajor allergens present in an area. However,airborne pollen is confirmed to be a sensitiveindicator of climate change. The observedshifts in the pollen seasons make necessary theadequate information for people concerned withpollen allergies, in particular for preventionand therapy purposes.

Airborne birch pollen in Neuchâtel (Switzerland): onset, peak and daily patterns

An accurate forecast of the starting point of thebirch pollen season in Neuchâtel can be made byadding the positive daily average air temperature fromFebruary 1st onward until the figure 270 is reached.At this point, the birch trees are ready to bloom.After that, the daily average temperature has toexceed 10 °C to allow pollen release.Today, the birch pollen season starts some 19 daysearlier in the year than in the 1980s, a consequenceof a recent climate change.The daily patterns of airborne birch pollen isirregular. Moreover, pollen concentrations frequentlyexceed the threshold of the appearance of allergicsymptoms, except during rainfall. Therefore, the onlybehavioral recommendation that can be given to peopleallergic to birch pollen is to shorten as much aspossible the contact with outdoor air during the mainbirch pollen season.

Phytophenological trends in the Swiss Alps, 1951-2002

This work aims to study the long term phenological trends in Switzerland and is focused upon the differences between the lowland (lower than 600 m asl) and the alpine regions (higher than 1000 m asl) for the 1951-2002 period. Trends for 651 time series (n >= 30 years) from 75 observation stations and 19 phenophases were calculated. Compared to the results obtained with the dataset 1951-1998, the proportion of the significant trends like the intensity of the trends calculated in days have been reinforced. In every season, a general earlier occurrence of the phenophases has been observed, except by the leaf fall, where a slight delay is more likely to occur. The proportion of significant trends is clearly higher in the alpine regions (42 %) than in the lowland (33 %). On the contrary, the shift towards earlier occurrences is stronger in the lowland. The spring phenophases occur 20 days in advance in the lowland and 15 days in the alpine regions, in summer 19 and 16 days, and in autumn 7 and 4 days earlier in the lowland and the alpine regions respectively. The proportion of significant trends in the regions located in the south of the Alps is remarkable: 64 % in the lowland and 50 % in the alpine regions. In this area, the small number of data only allowed the study of the leaf unfolding and the full flowering. Concerning the full flowering, an advance of 32 days in the lowland and 20 days in the alpine regions was observed. The leaf unfolding occurred 12 days earlier in the lowland and 1 day later in the alpine regions than 50 years before. The trends concerning the full flowering present a stronger trend in the south than in the north of the Alps. On the contrary, the trends concerning the leaf unfolding are stronger in the north. In Switzerland, the climate warming was stronger in the last decades than the global one. The increase in temperature reaches 1.5° for 100 years in winter and 0.4 to 0.8 in summer for the 1864 to 2001 period. As it was several times mentioned, the spring and early summer phenophases are above all influenced by the temperature of the air. Then the trend towards earlier occurrence of the phenological phases is clearly related to the climate warming. In autumn, apart from the temperature, other parameters such as dry periods during the vegetation period play also an important role. Short time weather events such as strong winds, frost or snow fall are the main drivers of the leaf fall. This study gives prominence that phenology is a good indicator of the influences of a climate warming on the development of the vegetation. Strong regional and altitudinal differences are observed in Switzerland.

Nonlinear short-term effects of airborne Poaceae levels on hay fever symptoms.

effects reporting system in countries using FFP-MB might also have played a role. Finally, a possible bias concerning the rate of declaration could be related to the clinician awareness of a possible increased rate of allergic reactions with FFP-MB following the prospective survey decided by Agence française de s ecurit e sanitaire des produits de sant e. However, one should notice that this increased rate of allergy reports has been rapidly detected before the active survey. Although the mechanism of this increased risk of allergic reaction remains to be elucidated, our results are a strong incentive for a thorough reevaluation of the benefit-to-risk ratio of pathogen reduction using MB.

Forecast of the Poaceae pollination in Zurich and Basle (Switzerland)

A simple formula, intended to serve as an aid for the prevention of allergies, is proposed for forecasting the starting date of the grass pollination season in Switzerland. Parameters are daily mean air temperature and rainfall. The forecast is accurate in two thirds of the cases, and too early in one third, but still useful in practice.

Effects of Airborne Birch Pollen Levels on Clinical Symptoms of Seasonal Allergic Rhinoconjunctivitis

Background: Most panel studies focusing on rhinitis and conjunctivitis symptoms and birch pollen have been performed on a linear basis and have not included air pollution and meteorological variables as potential confounders. The objective of this panel study was to assess the relationship between symptoms of seasonal allergic rhinoconjunctivitis and daily airborne birch pollen concentrations, checking with adequate statistical tools the shapes of concentration-response curves and controlling for confounders. Methods: The severity of rhinitis, conjunctivitis, and bronchial symptoms was recorded daily in March and April 2010 (3,311 person-days) in 61 seasonal allergic rhinoconjunctivitis patients sensitized to birch. Data were analyzed with generalized additive and generalized estimating equation models to quantify the effects of birch pollens. Results: The relationship between birch pollen and the percentage of patients with nasal, ocular and bronchial symptoms was linear until birch daily average concentrations of, respectively, 110, 70, and 70 grains/m3; it reached a plateau thereafter. For an increase of 10 grains/m3, the OR (95% CI) for nasal, ocular, and bronchial symptoms were, respectively, 1.07 (1.03-1.12), 1.17 (1.08-1.27), and 1.12 (1.03-1.21). At the beginning of the season, no nasal or ocular symptoms were observed below a threshold of 30 grains/m3. Conclusions: Adequate modeling regression shows that the clinical response to natural exposure to birch pollen in sensitized patients varies during Betula pollen season, with a threshold at the beginning of the season, while over the whole season the relationship is linear for nasal, ocular, and bronchial symptoms up to a saturation point, followed by a plateau.

Recommended Terminology for Aerobiological Studies

Aerobiology is an interdisciplinary science where researchers with different backgrounds are involved in different topics related to microorganism, airborne biological particles, e.g. pollen and spores, and phenology. Some concepts, words or expressions used in aerobiology have a clear definition, but are however frequently misused. Therefore, the working group “Quality Control” of the European Aerobiology Society (EAS) and the International Association of Aerobiology (IAA) would like to clarify some of them, their use and presentation.

Building models for daily pollen concentrations

We describe a method for constructing prediction models for daily pollen concentrations of several pollen taxa in different measurement sites in Switzerland. The method relies on daily pollen concentration time series that were measured with Hirst samplers. Each prediction is based on the weather conditions observed near the pollen measurement site. For each prediction model, we do model assessment with a test data set spanning several years.

Long-Term Urban-Rural Comparisons

The process of climatic warming during recent decades has had an effect on phytophenological commencement dates in Switzerland. In the period from 1951 to 1998 an earlier start of vegetation growth of roughly 11 days was recorded. In autumn, however, a slightly later commencement (approx. two days) of phenological phases has been noted. Depending on region and season, plants react in different ways. North of the Alps, a more marked trend towards earlier commencement in spring has been observed, whereas in the Rhone valley and South of the Alps, delayed phases clearly predominate in summer and autumn.

The importance of hornbeam (Carpinus sp.) pollen hypersensitivity in spring allergies

Hornbeam (Carpinus sp.) flowering occurs generallysimultaneously with birch anthesis. While birch pollenis known as the major tree-allergen in central andnorthern Europe, the quantitative and qualitative roleof hornbeam pollen in allergy has not been evaluated.In some regions of Switzerland, the annual ratiohornbeam SPI / birch SPI reaches 20–30% on average,and 50–180% some years. The relative importance ofhornbeam pollen hypersensitivity has been evaluated inmore than 200 patients suffering from spring allergiesto pollen during the last five years (1993–1997) inthe region of Geneva. Among symptomatic patientsduring the March-April period, 73.5% werehypersensitive to Betulaceae pollen. Overall, 71.7%of the patients allergic to Betulaceae pollen werefound to be sensitive to hornbeam, and 12.5% of thesame group of patients were sensitive to hornbeampollen only. Among this last group, half of thepatients, besides allergic rhino-conjunctivitis, werealso suffering from asthma. Hornbeam pollen isabundant and appears to have a significativeimportance in spring allergies. In some cases,specific immunotherapy to hornbeam pollen shouldperhaps be considered.