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The incidence
of hay fever in patients presenting to general practice
D.M.
Fleming and M Barley. |
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Birmingham
Research Unit of The Royal College of General Practitioners, 54
Lordswood Road, Harborne, Birmingham B17 9DB Hay fever is the name given to a condition
chiefly causing allergic rhinitis and conjunctivitis. In clinical practice,
episodes of allergic rhinitis are only infrequently diagnosed outside
the spring and mid-summer period. By implication it is associated with
hay but this impression underestimates the links with other plant pollens,
particularly tree pollens.
In the Weekly Returns Service of the Royal
College of General Practitioners we have monitored the incidence of
allergic rhinitis on a weekly basis since 1981. In figure 1 we present
data on the clinical incidence per 100,000 population in a surveyed
population of approximately 650,000. Each data point in the figure represents
the average weekly incidence level reported over the ten years 1994
to 2003. The figure clearly demonstrates two peaks of incidence around
weeks 20 and 24. In an examination of pollen data over the 10-year period
and covering the earlier of the two peaks we have observed a closer
relationship between oak pollen than with any other tree pollen. That
is not proof of a causal relationship but does suggest that the tree
or plant concerned pollinates at the same time as oak. The second peak
is associated with grass pollens. There is little variation in the timing
of these peaks from year to year but the magnitude varies and depends
on weather conditions. The incidence of hay fever episodes reported
in the Weekly Returns Service varies considerably with age. It is comparatively infrequently diagnosed
in preschool children and reported with maximum frequency in children
5-14 and young adults 15-24 years old.
As persons get older the relative effect of pollen allergies
diminishes and it is scarcely evident in the consultation data in persons
aged 65 years and over. The peak in the earlier tree pollen period is
particularly prominent in children but diminishes more rapidly as age
advances, than the equivalent incidence pattern in the grass pollen
period.. During the spring and early summer the
incidence of hay fever and asthma are closely related. This is particularly so in children and occurs
during both the early and late incidence peak periods. In preschool
children there are very prominent peaks of incidence of both asthma
and hay fever in the early and later peak periods.
In adults as opposed to children, the incidence of asthma attacks
is less strongly related to that of hay fever especially in the early
tree pollen period. The weekly data on asthma and hay fever
incidence, which has been collected over more than twenty years, show
a clearly increasing trend of asthma episodes over the 1980s rising
to a peak in 1993/4 and a consistently decreasing trend since, which
is evident in all age groups. The incidence of hay fever is more variable
and shows no clear trend. Allergic rhinitis is only infrequently
reported outside the pollen season whereas asthma episodes occur all
the year round. Most of the weeks in which surges of asthma attacks
are seen are the same as those in which respiratory infections are prominent. In May/October there is a surge of both
episodes of asthma brought to the attention of general practitioners
and prompting hospital admission. However, the surge in admissions is
relatively greater than that in practice reported episodes and this
apparent in all age groups; though particularly strong in children.
No increase in allergic rhinitis is present at this time and the cause
remains elusive. Spores and rhinovirus infection have been suggested
as possible causes but more research is needed to explain this phenomenon.
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