In this article we provide the first nationally representative estimates of household cockroach allergen prevalence and find that 11% of U.S. living room floors and 13% of kitchen floors exhibit elevated concentrations relative to a 2.0-U/g threshold previously established as related to allergic sensitization (Eggleston et al. 1998
). We also find detectable levels in at least one location of an estimated 63% of all homes.
In the National Cooperative Inner-City Asthma Study, children with sensitivity to cockroach allergen who were exposed to bedroom levels > 8.0 U/g had asthma hospitalization rates that were 3.7 times higher than sensitive children with lower levels of exposure (Rosenstreich et al. 1997
). On a national scale, we have found that 3% of U.S. living room and bedroom floors and 10% of kitchen floors exhibit elevated concentrations relative to this 8.0-U/g threshold.
Elevated cockroach allergen levels are most prevalent in high-rise apartments, urban settings, pre-1940 constructions, and households with incomes < $20,000. However, the allergen is not restricted to low-income environments; levels > 2.0 U/g were detected on the living room floors of 7% of households with annual incomes > $60,000.
Although there are some regional differences in magnitude, the same demographic factors are generally associated with elevated cockroach allergen levels in each geographic region. Demographic distributions themselves provide one possible explanation for the greater prevalence of elevated living room floor cockroach allergen in the Northeast compared with the South, because the Northeast target population includes relatively more pre-1946 constructions (43% vs. 14%) and more households in large urban areas (34% vs. 23%).
After accounting for the demographics, elevated exposure risk is most strongly associated with reported or observed cockroach activity and increases consistently with more recent or more prevalent activity. This is particularly informative in the context of cockroach allergen abatement studies that have focused on the impact of cleaning and insecticide application (Arbes et al. 2003
; Eggleston and Arruda 2001
; Eggleston et al. 1999
; Gergen et al. 1999
). Our results are consistent with the potential success of such a strategy. They also suggest that resident reports on cockroach activity alone may have some reliability as one indicator of such success, apart from in-house measurements or field staff observation.
Cockroach allergens are derived from several sources, including secretions, excretions, dead bodies, and associated debris. Airborne cockroach allergens are associated primarily with larger particles than are animal allergens, and after disturbance they fall and settle rapidly (Eggleston and Arruda 2001
). The generally low room-to-room correlations observed in this study suggest limited airborne transmission of the allergen, consistent with these physical properties. The results also suggest that the degree of correlation is associated with the method of cleaning; weaker correlations were observed among vacuumed surfaces compared with those that are mopped or swept. The practices of mopping or sweeping may tend to cause more spreading of the allergen and therefore higher correlation. Such causality is not conclusive, however. It is also possible that the observed correlation is a direct computational result of the generally higher concentrations observed in homes in which mopping and sweeping are employed. Residents reported that floors had been cleaned in most participating households within 2 weeks before dust sampling (89% of living room floors and 92% of kitchen floors).
The major strength of this study is its national representativeness. The weighted characteristics of the surveyed homes compared favorably with those of other national housing surveys (Vojta et al. 2002
). Our results illustrate the importance of achieving this nationally representative sample in characterizing exposure. Researchers who examined an intentionally nonrepresentative sample of homes in eight North American metropolitan areas reported detecting Bla g 1 (based on a lower limit of 0.4 U/g) in 9.4% of homes on average (range, 1.5–21.5%), using a combined dust sample collected from multiple household sites (Huss et al. 2001
). In contrast, based upon a weighted average of concentrations from all household sites and a nationally representative sample, we found detectable concentrations > 0.4 U/g in 27.4% of U.S. homes.
The major limitation of the study is its cross-sectional design. Dust samples were collected at a single point in time because repeated visits to the home were not feasible. However, this was the most efficient method for achieving the stated objective of estimating and characterizing indoor allergen levels on a national scale. Sampling was conducted across seasons so as to mitigate any possible seasonal bias.
This study surveyed homes for the Bla g 1 allergen from the German cockroach Blattella germanica
, a small organism responsible for the primary U.S. exposure. The estimated prevalence of detectable Bla g 1 concentrations in 63% of homes is consistent with other research that found 52% prevalence in a regional sample of child care facilities (Arbes et al. 2005b
). Nevertheless, our absolute estimates of the prevalence of detectable concentrations may be affected by greater assay variability at very low concentrations and should be interpreted with some caution. They are reported in primarily to support comparative analyses and are shown together with the likely more stable results at the 2-U/g and 8-U/g thresholds. Our results relative to these thresholds are also very consistent with the aforementioned child care study, which found that 10.4% of daycare floor Bla g 1 concentrations exceeded 2 U/g and 2.3% exceeded 8 U/g (Arbes S, personal communication).
This study characterizes the prevalence of cockroach allergen in U.S. homes and illustrates factors influencing the risk of exposure to elevated concentrations. These results may help clinicians to assess whether a patient is likely to be exposed and suggest measures to reduce this exposure. Our results also lend important context to the potential impact of abatement studies of cockroach allergen.