Biological contaminants —illness syndromes; bacteria; viruses; and exposures to insect, mite, and animal allergens - Indoor Environmental Quality - page 158

tization is among suburban dwellers, and the lowest is in low-income urban
areas (where cockroach sensitization is high; Table 5.4 ) . It has been estimated
that 6 to 10 million individuals in the U.S. are allergic to cat allergen.

A. Cat allergens
Fel d I, the major cat allergen, is an acidic glycoprotein found on hair and
skin scales, and in saliva, sebaceous gland excretions, and voided urine. The
antigen is dispersed by licking and grooming activity. Allergen production
is voluminous, with a single cat in an indoor space producing 3 to 7

g Fel
d I/day. The size range of particles that contain cat allergen varies from <2.5
to 10

µ

m. Because of this small size,
cat allergen particles become airborne (even in undisturbed situations) and
remain airborne for extended periods of time (hours). As such, humans have
a high probability of being exposed to cat antigens that produce sensitization
and allergic or asthmatic symptoms. Higher airborne cat allergen levels are
associated with greater numbers of cats present and low building air
exchange rates. Relative concentration categories of cat allergen in house
dust are summarized in Table 5.6 .
Cat allergen is ubiquitously found in building dust samples collected in
residences, schools, medical facilities, retail establishments, and a variety of
public places. This ubiquitous presence of cat allergen results from its passive
transport on the clothing of individuals in cat-owning households (as well
as visitors). Concentrations of cat allergen measured in the floor dust of
elementary schools can be seen in Table 5.7 . Of these, >20% of floor dust
samples had cat allergen concentrations that are reported to cause a moderate
to high risk of sensitization on exposure.
Concentrations of Fel d I in building dust of <1

µ m, with a very large percentage <2.5 µ

g/g are considered to
pose a low sensitization risk; concentrations of 1 to 8

µ

µ g/g pose a major

sensitization risk; and concentrations >8 µ g/g pose a major risk of causing

acute asthmatic symptoms ( Table 5.6 ) .
Concentrations of Fel d I in houses with cats commonly exceed 10 µ g/g

floor dust; in cat-free buildings, concentrations are typically <10 µ g/g but

often near or above the 1 g/g threshold for sensitization. Highest concen-

trations are found on living/family room floor surfaces in residences.

µ

Table 5.7 Prevalence (%) of Cat and Dog Allergens
in Floor Dust Samples in Midwestern U.S.
Elementary School Classrooms
Allergen concentration ( µ g/g dust)

Allergen <1 1-8 >8 Range

Cat (Fel d 1) 77.1 20.0 1.4 ND-57.2

Dog (Can f 1) 2.9 88.5 8.6 0.5-57.3

ND = not detectable.
Source: From Godish, D., unpublished data, 1998.