Understanding pollen and mold counts
For the 35 million Americans who have seasonal
allergies, rising pollen counts in the spring bring symptoms that can ruin a
time of year the rest of us enjoy immensely.
Allergy symptoms are not only annoying, but for
many people interfere with their ability to work, perform at school, or even
sleep. Understanding the significance of pollen and mold spore counts can help
better manage symptoms.
Pollens and molds represent the clinically most
important outdoor allergens. Researchers are interested in pollen and mold
sampling because these airborne allergens occur in easily identifiable units.
Attempts at counting pollens go back over 100
years. Initial investigators collected particles on an adhesive coated slide.
However, variables such as wind speed and particle size changed the number of
particles coming to rest on a slide, affecting the accuracy of this method.
More recently, researchers have developed
volumetric techniques that measure the concentration of pollen grains or mold
spores in the air. This gives them a better estimate of how much pollen people
in the sampling area are being exposed to.
Two of the more popular volumetric samplers used
in this country over the past few years are the Rotorod sampler and the
Volumetric Spore Trap. The Rotorod sampler uses small adhesive coated rods that
intermittently spin through a certain volume of air so that the particles in
that air stick to the rod. At the end of 24 hours, the particles are identified
under a microscope and the concentration of particles per cubic meter of air is
Rotorod sampler does a good job collecting pollens and larger molds. However,
smaller mold spores are not as efficiently collected resulting in low estimates
for counts of certain mold spores.
Volumetric Spore Traps draw air into the sampler
at a given rate. The particles in the air land on an adhesive coated microscope
slide. After a period of sampling, usually one day, the sample is stained and
the pollen grains and mold spores are identified and counted, and the
concentrations in the air are calculated.
Regardless of the method used, the reported
counts reflect the average count for the sampling period, not a real-time count
determined at the time of the report. For example, a pollen count reported on
Monday probably represents the average count for the 24-hour period ending at
some time on Monday morning.
Because various pollen and mold counts vary over
the course of the day, the average count gives us an estimate of overall
exposure. At certain times during the day, the concentration of various
particles could be temporarily higher.
The American Academy of Allergy Asthma and
Immunology (AAAAI) organized the Aeroallergen Monitoring Network, which has
compiled pollen and mold counts for more than 30 years. The network was
established to further the science of allergy, and to contribute to the
information available to physicians for the diagnosis and treatment of allergic
The Network has reported pollen and mold spore
counts to the public and the media since 1992 through the National Allergy
Bureau, a service established by the AAAAI. Member stations report pollen and
mold counts to the NAB which releases reports to interested media outlets and to
the public through the AAAAI web site (www.aaaai.org/nab). Results are reported
as total tree pollen, grass pollen, weed pollen, and mold spore counts per cubic
meter with comments about their relative amounts. This information allows
allergy sufferers and their physicians to correlate symptoms and causing
Accurate forecasts of future counts would allow
people to adjust activities on days with predicted high counts. Forecasting
involves having accurate counts from previous years at the involved site and
taking into account meteorological data.
Researchers involved with the network are working
on such predictive models, but want to prove their reliability before making
such predictions available to the public. Until reliable forecasts are
available, people with symptoms will have to rely on trends in recent high
pollen counts to alert them to take appropriate precautions regarding avoidance.