Hay fever index

Spring is coming to an end and summer is quickly approaching. Nature is blooming and there are plenty of grass pollen, too. People who suffer from hay fever sneeze, have blocked noses and itchy eyes as an allergic reaction to the pollen from trees and grasses which are released into the air. As more and more people are suffering from allergies including hay fever, this is becoming a growing problem in society. More insight is needed.

Existing sources such as the Hay Fever Radar and surveillance data from Dutch health care research institute NIVEL do provide insight into pollen flows and number of hay fever patients who visit a GP.
Not everyone who has hay fever related complaints will visit a GP and a pharmacy. They may also go to the local drugstore for self-medication products. This could be medication in the form of tablets, nose sprays or eye drops which curb the allergic reaction.
For this publication, the CBS Centre for Big Data Statistics (CBDS) studied whether weekly sales data on hay fever medication at pharmacies could be used as a new source in order to provide an overview of how the hay fever season progresses.

Increased sales

In the figure below, the turnover index for hay fever medication shows the development of weekly sales of hay fever medication relative to the average weekly turnover in 2016. The same figure displays the changing count of allergenic pollen in the air (source: Pollen counts at Elkerliek Hospital) It also shows the pollen counts of tree and plant varieties which trigger moderate, severe or very severe allergic reactions, such as the hazelnut tree, alder, birch, Poaceae, Rumex, Plantago, Cedar of Lebanon, Artemisia and Ambrosia.

Turnover in hay fever medication and pollen concentrations in the air
   Turnover index medication (2016=100)Most allergenic pollen per m3 of air
2016126.524
223.43
322.413
424.3107
527.51013
632.9269
730263
835.2179
934.9133
1065.9276
1195.3303
1273.4199
1392.442
14134.71177
15228.43475
16179.9363
17108.6282
18326.3711
19373.3231
20182.9204
21259.785
22510.4506
23561.1563
24159.939
25142.1167
261130
27135.2510
28119.1195
29123181
3088.416
3168.768
3262.198
3367.782
3465.1105
3557.273
3654.5102
3753.344
3851.848
3944.771
4041.79
4133.79
4229.73
4328.11
4425.40
4522.51
4621.41
4723.61
4822.40
4920.70
5022.50
5127.20
5226.66
2017124.96
222.521
322.17
424.910
525.918
6233
731.2351
840.4880
953.8150
1065.347
11111.3124
12110.79
13221.32623
14184.81017
15172.5381
16120.8143
17115.393
18126.764
19144.726
20171.5171
21420.1
22505.9290
23272.9307
24297.9139
25238235
26126122
27129.6156
28103.781
29109.325
3083.364
3173.950
3262.663
3356.965
3464.662
355626
3644.37
3737.725
3837.731
3933.917
4030.520
4130.56
4230.11
4330.61
4430.21
4527.40
4624.90
4725.70
4825.50
4921.93
5025.10
5133.22
5232.648
2018129.15
227.270
325.923
431.8143
534.460
631.2143
733.1262
838.3217
933.584
1058.91054
1183.3237
1266.742
1378.58
14126.1330
15263.23709
16540.14398
17257.8380
1823145
19293.788
20204.9120
21607.4661

Early in spring around the beginning of April, an increase in sales of hay fever medication can be seen. This is also the period in which pollen of certain trees such as birches trigger allergic reactions. Grass pollen appear later in the season, which is also the time of year when the highest sales peak is recorded. Although the grass pollen count is not extremely high, many people suffering from hay fever are sensitive to grass pollen, which may explain the sales peak. Sales figures are therefore not always directly related to the pollen count in the air; sales are primarily related to the severity of the symptoms experienced by hay fever sufferers.

Figure 2 shows that the hay fever season started slightly later this year compared to 2017. Interestingly, a high sales peak was nevertheless already recorded in April of this year. GP visits on account of hay fever are displaying a similar trend (source: NIVEL surveillance). This peak may be related to the warm weather last April, which caused the release of many tree pollen into the air.

 

Turnover index of hay fever medication, weekly (2016=100)
   201620172018
Mar934.953.833.5
1065.965.358.9
1195.3111.383.3
1273.4110.766.7
1392.4221.378.5
Apr14134.7184.8126.1
15228.4172.5263.2
16179.9120.8540.1
17108.6115.3257.8
May18326.3126.7231
19373.3144.7293.7
20182.9171.5204.9
21259.7420.1607.4
22510.4505.9
Jun23561.1272.9
24159.9297.9
25142.1238.0
26113.0126.0
July27135.2129.6
28119.1103.7
29123.0109.3
3088.483.3
Aug3168.773.9
3262.162.6
3367.756.9
3465.164.6
3557.256.0
Sep3654.544.3
3753.337.7
3851.837.7
3944.733.9

 

Last-minute purchase

Data further show that people tend to purchase medication only when the pollen are released into the air, rather than stocking up on medication beforehand. It does not look like people only purchase medication at the beginning of the season for long-term use. In general, there is a clear trend that when pollen concentrations increase, sales increase as well, even later on in the season. In short, sales data of hay fever medication obtained from chemists seem to provide a fairly accurate picture of the duration and intensity of the hay fever season.

 

Explanations

CBS obtains transaction data from a large portion of the pharmacies in the Netherlands. The data are more commonly used as input for the consumer price index. In this collaboration, pharmacies have indicated that their data may also be used for statistical research purposes. Weekly sales data of around 30-40 different products used to alleviate hay fever symptoms have been used to produce the hay fever index. The turnover index is not intended to show the total sales volume of hay fever medication in the Netherlands, but to provide more insight into the development of the hay fever season and times when consumers purchase medication.

 

Feedback: 

We would like to know your opinion on this beta product and its potential applications. We are open to ideas on how this social phenomenon can be described more accurately using new data sources. Please use the form below to submit your feedback.