Background: Cockroach allergen is recognized as a causal factor for asthma. However, airborne cockroach allergen has not been detected in undisturbed conditions, and therefore the behavior and properties of airborne cockroach allergen have been poorly characterized. A new aeroallergen sampling method and sensitive system of immunoassay have been used to examine cockroach allergen exposure. Objective: Our purpose was to measure and characterize airborne cockroach allergens during normal domestic exposure in the homes of Sydney, Australia. Methods: Air sampling with Institute of Occupational Medicine, Edinburgh (IOM) samplers was performed in the living rooms of 10 houses during low- and no-disturbance environments, In addition, inhaled particles were collected by each home occupant during low domestic exposure with use of intra-nasal samplers that impact particles onto an adhesive surface. The particles collected on the IOMs and the intranasal samplers were immunostained with Bla g 1 monoclonal antibodies. Particle size, morphologic characteristics, and the relative Bla g 1 content of particles were estimated. Reservoir dust samples from the kitchen, living room, and bedroom were assayed by an ELISA. Two forms of repeatability of IOM air sampling were examined, The first measure tested the repeatability of 2 IOM samples collected simultaneously in the same room during low- and no-disturbance activities. The second measure examined the repeatability of IOM;I sampling over time on 10 consecutive days. Results: Bla g 1 was detected in reservoir dust samples taken from all homes (geometric mean 1.5 U/g, range 0.2-9.4 U/g), Inhaled particles containing Bla g 1 were detected during 1 hour of intra-nasal sampling in 8 of 10 homes during low disturbance. Cockroach particles were detected on all of the IOM samples collected for both 4-hour low-disturbance and overnight no-disturbance sampling environments. Particles containing Bla g 1 collected with the IOM samplers during low disturbance ranged in size from 3 to 350 mu m. These particles are amorphous and irregular in shape, and a majority of the large particles were described as flakes (flat, transparent particles) and fibers (threadlike). A relationship was demonstrated between the allergen content of cockroach particles and their particle size. The larger particles elute more Bla g 1, The coefficient of repeatability for measurements made during low and no disturbance was 3.62 and 2.09, respectively. For measurements repeated over time at the same site, the coefficient of repeatability was 2.61. This represents the fold range within which 95% of pairs of measurements made at an interval of 1 day would be expected to lie. Conclusions: Airborne cockroach allergen is present in both undisturbed and low-disturbance environments in homes with relatively low reservoir levels of Bla g 1. In agreement with previous reports, airborne particles containing cockroach allergen (Bla g 1) are mainly associated with particles >10 mu m. These particles are amorphous and irregular in shape and can be described as flakes and fibers.
